- For those not familiar, the secret ingredients are to do with the Lime Cycle [1]:
1) Quicklime/Slakedlime (Calcium Oxide, CaO)
2) Lime (Calcium Hydroxide, CaOH2)
3) Limestone (Calcium Carbonate, CaCO3)
To keep it simple, typically you start with Quicklime (CaO) and after construction you end up with some mix of all three and after hundreds of years, the masonry transitions to mostly Limestone with microscopic traces of the other two. The slow transition of the lime cycle upon exposure of the masonry to both air and water (rain) ends up making the structure "self healing" and "stronger over time".
Fun fact! Lime putty is anti-mold even in humid conditions because upon exposure to moisture, CaOH2 + H20 becomes too basic for mold to grow on.
Cement/Concrete (based on Portland cement) is water proof but Lime by itself is not. But Roman Concrete, made from Lime and mixing with ash or broken pottery or ceramics makes it water proof [2]. I beleive Roman concrete was used whenever contact with water was expected. Both concrete and Roman concrete have the same underlying chemistry (Pozzolanic reaction) to make them water proof [3].
The fascinating thing is that Lime is everywhere in ancient masonry. Lime is more breathable, workable and sustainable. The only thing is, it requires maintainance, which is why Portland cement has taken over the world.
Modern cement/concrete is amazing for large structures. I hope Lime makes a comeback soon at least partly as putty and for building smaller homes.
[1] https://en.wikipedia.org/wiki/Lime_(material)
[2] https://en.wikipedia.org/wiki/Roman_concrete
[3] https://en.wikipedia.org/wiki/Pozzolanic_activity#Reaction
- > The only thing is, it requires maintainance, which is why Portland cement has taken over the world.
What kind of maintenance and why did roman cement survive without it? Or are we simply looking at ancient survivorship bias where the surviving roman concrete structures survived through the lime cycle without maintenance until it was no longer required?
- Victorian brick houses are all lime based, pointing (mortar between bricks), render outside and internal plaster. (Ours is 140 years old ish).
Lime is also more flexible (these houses have minimal to no foundation and constantly move), it’s breathable (no/less damp) and as such it also improves air quality indoors. It’s annoying to do because drying times are days/weeks not hours, but long run it’s a far superior material for small buildings.
It does burn though if you accidentally get it on your skin!
- >Fun fact! Lime putty is anti-mold even in humid conditions because upon exposure to moisture, CaOH2 + H20 becomes too basic for mold to grow on.
Can we use this instead of grout in the bathroom somehow?
- I'm not sure as I'm not a builder or plasterer and it does depend on the use case.
However I do know that some grout and some paints that say they are anti-mold contain Lime or calcium hydroxide as their primary anti-mold ingredient. I think pure Lime putty can be used as pointing material between bricks in humid basements. Lime plaster (lime mixed with sand) can also be used in bathrooms (with some considerations I am not familiar with). So, my best guess is that some mix of Lime can be used as grout. But I can't say for sure.
Something I plan on doing before this winter is to use Lime Wash. Take Lime (CaOH2 in powder form) and mix with water until it has milk like consistency and brush it on grout or on (white) bathroom walls. If it works, I expect it to be a yearly or quarterly ritual and not a one time solution.
EDIT: A fascinating historical material I recently learned about used in bathrooms is called Tadelakt [1] which uses Lime as one of its ingredients.
- I like the idea of treating limewash as maintenance rather than a permanent cure. That is probably closer to how these materials were historically used anyway
- I just restored an 1800’s house and we redid the paint in limewash as part of that process. (Effectively zero VOCs but pretty caustic when wet.)
Historically (for interior paint) you would use regular limewash in dry spaces and add casein/milk in high traffic/wet spaces. It works in a bathroom but wouldn’t hold up in a shower (for that you would want to use “tadelakt“ - especially if you’re going for that Aman spa look).
The contemporary solution with modern limewashing is to use “mineral shield” - it uses silicone instead of casein - it makes water droplets bead up but still lets water vapor breath through.
It also doesn’t flatten out the nice velvet texture one gets with limewash paint from the calcite crystals.
That said, it’s extremely obvious if one touches up a patch of wall with limewash. No two batches are the same color unless you’re going pure white and even then…
- Lime wash also discourages people from leaning against the wall, once they have seen the white marks on thier suit...
- In my experience, grout doesn't go mouldy but silicone sealant certainly does. It's the caulk and the sealant that you want, i think, to replace
- There is a variation of lime wash that includes a fatty oil as a sealant and has been around for 100s of years
- In India, people have used lime for all sorts of things in houses, including grout in places. It requires yearly maintenance.
- Pure silicone caulk is mold-proof, even in the white variation. The various "improvements" in many caulks allow mold to get a foothold.
- After decades of owning multiple bathrooms and only using products advertised as 100% silicon caulk, I can assure you that it is not mold-proof.
- it's not waterproof
- Neither is grout. Grout is water permiable. You shower is water proof from the water proof backing we install the tile on top of.
Cement board + roll on or something like kerdi system.
- This is why you pay the premium for epoxy grout. When we redid our house we used only epoxy grout and cleaning it as as simple as using a foaming tile spray.
- This is not always a great idea. Especially if you have a water proofing membrane that allows drying out. You never want to trap moisture in a cavity. You want to be able to dry into the wet side.
- My shower is waterproof because it’s a one-piece insert made of plastic.
Other shower materials that aren’t absolutely insanely stupid include glass, quartz, and other non-porous materials.
Because biology.
- right, but lime will be washed away by the water if no waterproof layer is added
- It is not lime as in the fruit, it is lime as in the material (CaOH2). Lime the material is the binding agent in lime plasters. It is not likely to get washed away.
- caoh2 is water soluble (slightly). the question was about anti-mold properties and it is commonly used for these properties in paint for example in cellars but it will lose these properties when too wet. so it's not used in bathrooms.
- Sure but lime plaster can be used in bathrooms on the non shower walls as there's no running water but lots of moisture/humidity which leads to mold growth. As far as using it in the grout behind tiles, you may have a point.
I'm considering applying lime wash between the tiles regularly but not sure what the results will be.
- >Cement/Concrete (based on Portland cement) is water proof
That's patently untrue. Otherwise we wouldn't need concrete sealants.
- You are correct.
I'm not sure why I remember cement to be water proof. Its possible I infered from how its been used around me. I have seen cement very often used where water contact is expected (bathrooms etc). I have also seen brick walls plastered with an extra layer of cement as putty considered to be rain proof and any leaks were thought of as poor workmanship rather than poor material choice.
P.S. I'm not a builder. I've taken an interest in the topic a few months ago.
- Might be because it's water tolerant, i.e. it doesn't break down with exposure to water? Roman über-concrete stories are always full of "check out the concrete that's sitting in sea-water, it's still going strong! maybe it even helps!" cases too.
- Hydraulic cement is made for some of those occasions:
https://www.quikrete.com/productlines/hydraulicwaterstopceme...
But I wouldn't want to make any sort of building that only relied on it for waterproofing.
- [dead]
- You can also just see it with cement board - if you pour water on top of it, it will eventually migrate through and drip.
- Also if you put a slab basement in a hillside in a rainy area. Water will percolate up through the slab unless you make good drains to divert the water around your foundation.
- The key here is “based on Portland cement”, which is generally has water repellent added to it making it water proof.
Normal cement, concrete .. Is a different story.
- I'm not sure exactly what you're saying is correct.
'Concrete' is a combination of sand, cement, water and aggregate, that cures together to form.
When the water migrates away from the curing concrete, it leaves open pores behind that future moisture can move through.
- Concrete is generally porous and definitely not micro-waterproof (aka lots of water vapor makes it’s way through). Including if using Portland cement.
It is generally macro-waterproof, however, unless there are large cracks.
- I forgot another important reason why Portland cement is preferred over lime these days. Lime takes a while to set (a few days?), cement sets faster.
- > Lime takes a while to set (a few days?)
Up to 30 days to set, and depending on the type of lime (hydraulic or non-hydraulic) and form/process (putty, hot mix, etc.) up to a year to reach full hardness.
- Cement will still take many days to reach full cure time (measured in increasing PSI ratings)
https://www.ce.memphis.edu/1101/notes/concrete/section_3_pro...
- But it will be set enough to keep laying bricks tomorrow. Lime on the other hand takes a bit more thought. It is doubly true if the weather is cold
- You aren't contradicting anything. MOST of the strength is achieved in 24 hours or less.
- [dead]
- This makes me want to see lime used more in ordinary homes
- > Lime is more breathable, workable and sustainable. The only thing is, it requires maintainance
What sort of maintenance does it need?
- It wears down quicker than concrete (you can scratch it easily with a nail and minimal pressure). But we’re still talking 50+ years (before repointing brick, in my case). As long as maintained it’ll last forever (our home is 140 years old, I just re-did the pointing, should be good till I die).
- TLDR, use lime mortar not portland cement. And don't use rebar.
Also- modern concrete is not waterproof... requires sealant
- > It turns out that another chemical reaction, known as carbonation, might also contribute to Roman concrete’s longevity.
Roman concrete was made lime cement (calcium dioxide); which cures via carbonation (hardens with carbon oxide). And adding pozzolan to lime makes it hydrolic (hardens with water). Is it surprising that it can still carbonate some? Modern concrete has steel which rust and crack concrete. You can use fiberglass rebar for longevity, or build without rebar even, but that is more costly and and less efficient.
- Stainless steel rebar is a thing. It's expensive, but structures built with it last much longer. Washington State now has a policy that bridges over salt water will be built with stainless steel rebar. Stainless steel costs much more, but total project cost goes up less than 10%.
Epoxy coated rebar looked promising for a while, but it's on the way out. Water gets in at cuts and joints. So all field joints have to have field patching.
There is a great comparison. Two piers were built in the 1940s, side by side, one with carbon steel rebar, one with stainless steel rebar.[1] Go look.
[1] https://worldstainless.org/wp-content/uploads/2025/02/ref19_...
[1] https://worldstainless.org/wp-content/uploads/2025/02/ref19_...
- > Stainless steel rebar is a thing. It's expensive […]
That's an understatement. Fiberglass (GFRP) tops out at roughly US$ 2.50/foot, while SS can get up to $9:
* https://www.wellcoindustries.com/the-cost-of-rebar-and-the-c...
The low-end of plain steel rebar is $0.40.
- As the GP noted, it's still only a small bump in overall cost.
- Also lower TCO, total cost of ownership.
- There's also Glass Fiber Reinforced Polymer rebar but I don't know much about costs and how good it is vs stainless steel rebar.
- > Stainless steel costs much more, but total project cost goes up less than 10%.
I think people are often surprised how little materials cost affects the total cost of a job.
I'm having this argument at work, where I want some more expensive cabling installed in a bunch of offices across Scotland so it doesn't need to be done again in another ten year's time, but "that stuff is so expensive, do we really need it?" is what I'm running up against.
So as it turns out today I'm giving them a breakdown of the cost of the job. Guess what the expensive bits are?
Did you guess "wages for two guys, hotel rooms for two guys, 800 miles of diesel, and a couple of ferry tickets?"
Well, you're way ahead of today's crowd then.
- I've worked on a few big EPC projects in a specialised industrial sector, including some in the UK. Three things drive the first digit of cost, assuming you've hired relatively competent engineers and constructors:
1. (Design) Building floorplate and architectural complexity (i.e., divergence from 'big box')
2. (Construction) Schedule adherence. Almost any one-off expense to stick to the schedule is worth it, but to your point, these are often challenged or delayed. Building and testing equipment on skids off-site is almost always worth it.
3. (Design/Commissioning) Schedule adherence. For commissioning this is typically driven by design choices (did you pick a high-TRL process, or if not, do all the work required to mature it in parallel to construction?) and by building the right commissioning team (knows their job, knows the plant).
If more expensive plant & equipment gets you ahead on any of these 3, 99% of the time that is an overall optimisation.
- I was once working on a one off build and also on a smaller build at the same time. The smaller build was built start to finish as per the plans, the larger one was choices all the way.
The net result, we topped out and roofed the big house, then built the small house in its entirety while the owners of the big house chose their windows. Add that in favour of waterfall design...
- Not permitting and regulation? We're told that is the biggest impediment to development.
- Permitting and regulation is generally a sub-component to each of the three things mentioned, and can be a major factor in schedule adherence for large scale construction projects. Whether that is the primary impediment or not is often a factor of the specifics of the project (and its design) and the overall environment. During major events (e.g. COVID), materials access and availability was a far more challenging aspect of schedule adherence for most large projects than any other factor.
I've never worked in this field as the GP, but I have family that do and I've heard plenty of stories and made my own observations, but definitely take my two cents with plenty of salt. Maybe GP will reply also.
- In general, in the UK, labour costs dominate. How do people not understand that?!
This is what's interesting with AI pricing at the moment - it has gone from "a fraction of the equivalent labour cost" and so people have tried to cut staff, and is moving to "on par with labour cost" and all the calculations change.
- Not just the UK, labor is usually the dominant cost of anything.
Our house flooded about half a foot a year or two ago. I had to replace all the baseboards. The damage was assessed at $40k. I tried to contact contractors to do the work, but the job was so insignificant compared to other jobs in the area, and we were in the middle of getting our house raised, that it was taking forever.
Including tools I did not have prior, material costs ran about $5k - $7k. I did the work around my job and other obligations, so about one day a week for a couple of months. If I were to honestly guess, it probably took me about two weeks. And that's measuring, cutting, installing, caulking, and painting. And there were some inefficiencies in my process.
- I hope you’re prepared for a huge amount of bike shedding… but if we pick this color, we can save a couple of dollars…
- It's going in a suspended ceiling so it has to be purple.
- >I think people are often surprised how little materials cost affects the total cost of a job.
Because people don't understand how much compliance and box checking and check the guy who checked the last guy's work there is in a "you need government permission for this and not the easy permission they give a homeowner deck project" sized construction project.
- > I think people are often surprised how little materials cost affects the total cost of a job.
It's because they frankly never did it. Nobody that had to contract something around the house is surprised by cost like that, it often costs more than price of renting equipment + you doing it yourself 3 times slower than an expert would did it, even if you're paid well.
There is reason there is so many DIY channels, labour costs are high and install costs of some stuff can be ridiculous (like 2 hour job to install AC costing more than cheap AC unit).
That's also partly the reason the more expensive materials are used - if they offer savings in labour (say way faster to put in), they might be worth it vs paying someone for more hours
- It's why plumbers use $25 sharkbite fittings now instead of soldering in a $2 copper fitting. But of course the sharkbite relies on a rubber O-ring and will probably leak in 10 years, the plumber will be long gone or the property probably under new ownership who don't remember.
- Softalker is right-on in his warning:
We usually have a few freezes in the winter and some homes' pipes freeze. I was surprised, in speaking to a plumber, to find that pipe clamp installation had come to dominate the repair market (as opposed to repairing/replacing the leaky pipe).
In his first year this plumber had arrived at the plumbing supply house to find all pipe clamp orders backlogged two weeks! He thus determined to, during the warmer months, stockpile a cache of pipe clamps for the coming winter.
Furthermore, as SofTalker states, the fitting is usually left in-place instead of being replaced! Yet one more reason to have a prospective home inspected by someone who is very knowledgeable.
- Yeah. I mean I just had some concrete slabs laid to put a bike shed on (literally bikeshedding, the colour is green, that's what it comes powdercoated in from the supplier, take it or leave it).
It was 300 quid.
I could not buy the materials for 300 quid.
Two guys showed up with eight slabs, half a tonne of Type 2 and half a tonne of sand, and then the next day the landscaper showed up and did about six hours of work to dig it all out, fill it all in, and put the slabs down.
It's absolutely perfect, exactly how I wanted it, and it would have taken me a couple of days and cost far more - and I'm quite good at that kind of stuff, it's just not what I do all day every day so the landscaper will be far better at it.
- My experience when i was in the trade is very few people know what perfect looks like, and so are perfectly willing to forego decent workmanship in favour of cheap. One of the reasons I left the trade, you could make more money doing a bad job, and I had no desire to do that.
- > Two piers were built in the 1940s, side by side
As far as I can tell, only one pier was built (using stainless steel rebar) and the presentation is comparing it to a hypothetical alternative as a theoretical exercise: "What if the Progreso Pier was built using carbon steel rebar?"
- I think that was the prior pier maybe in the picture? The main pier only has one - it’s massive and goes forever. Pretty beefy construction too given that it takes a lot of heavy trucks.
Progreso - great pier and a great kiteboarding spot.
- As I understand it, concrete has excellent resistance to compression but fails easily on traction, while steel bars are exactly the opposite. That is why you put rebar in concrete: the steel handles the traction loads and the concrete handles the compression. This works well because both materials have similar coefficients of thermal expansion, so as the temperature changes they both expand and contract at the same rate. I suppose you can engineer fiberglass to have the same thermal expansion coefficient and use it to replace steel (assuming it is just as strong on traction). But how would you "build without rebar even"? Wouldn't your beams start cracking at the bottom, where they are subject to traction?
- To build without tension you have to build structures that basically look like Roman structures [1]: a bunch of tightly spaces arches so that the entire thing is in compression, with no meaningful tension anywhere.
But it turns out that's pretty inconvenient; we really like doing dozens of feet of span for highway overpasses, building floors, and everything else. So we put rebar in all the concrete and just acknowledge that that means it has an absolute maximum lifespan of a century or two, and will certainly not last for millennia the way pure concrete in pure compression can.
- The “it’s built so everything is under compression” is great thing to bring up, but fyi your link is AI generated, filled with senseless repetition and “it’s not just x, it’s y”.
Looking it up on archive.org shows it was generated this year.
- Blah, so you're right. I was just looking for a link with some representative reference pictures, but I should have done more diligence. Thanks for pointing it out.
- They could do large arches too, see https://en.wikipedia.org/wiki/Basilica_of_Maxentius
- > To build without tension you have to build structures that basically look like Roman structures [1]: a bunch of tightly spaces arches so that the entire thing is in compression, with no meaningful tension anywhere.
Until an earthquake occurs, and then all of those mostly-down forces turn into side-to-side forces.
- or go and revive Gothic architecture
- > Wouldn't your beams start cracking at the bottom, where they are subject to traction?
You have a few mistakes here. I’m not trying to demean you, but I’m going to number them just for clarity, as it can get confusing when there are many misunderstandings.
1. You are intending to ask about tension (which the rebar helps with), not traction (the force your tires exert against a road).
2. Tension is not only experienced at the bottom of beams, the location with the most tension will depend on the geometry. For a vertical beam, I think tension will probably be pretty even through the whole beam in most “normal” designs and loading configurations. But it will really depend on the geometry and on the loads being applied.
3. I think when you say concrete beams you’re meaning columns (apologies if I’m wrong about this). Concrete columns are remarkably good at holding up without rebar, because they experience almost exclusively compression! And indeed, ancient Roman designs did not use rebar at all :). It’s certainly possible.
- 1.- My apologies for the terminology - I took one overview class on the subject in Spanish, and haven't looked at it in the last 60 years. 2.- Agreed - that's why rebar on horizontal beams (and slabs) sometimes goes on the top edge and shifts to the bottom edge. 3.- By beams I do mean horizontal beams. This also applies to horizontal slabs. However, vertical columns also need rebar, especially in earthquake-prone areas. If the ground moves horizontally in an earthquake, the (vertical) columns have to transmit the motion to the upper parts of the structure. This create huge tension stresses on one side of the columns so they need vertical rebar rods on their perimeter.
- > 1. You are intending to ask about tension (which the rebar helps with), not traction (the force your tires exert against a road).
I don’t know if it is the case here, but it is a common mistake for some non-native English speakers. In some languages traction is a false friend.
- And in English, traction also means pulling, but it got somewhat misapplied to the friction of tires, causing confusion in the language. For example, a tractor is something that pulls, and when a broken leg is put in traction, it's suspended to pull it apart and keep the muscles from pulling it together.
Tension, as you say, is indeed the term used in physics and engineering for the force on an object pulling it from either end.
- > exactly the opposite
No, steel is better in both ways, ten times over. It's just more expensive, concrete is a "filler" to cheap out construction.
If you think about it, all engineering is about cheaping out things. It's pretty easy to build awesome projects having unlimited budget.
- As one of my professors said back in time: "Steel is one of the best materials for a number of applications. We don't use it only because it's abundant. "Abundant" and "good" are not always mutually exclusive."
- Just FYI, I think you're looking for "(in) tension" instead of "(on) traction".
- There's also stainless steel rebar
- Even without the rebar rusting, I think you can still have issues with the steel and concrete having difference thermal expansion properties, particularly for outdoor strucutures where a freeze/thaw cycle is in play.
Basically the rebar works itself loose over time and creates micro-fractures in the concrete that then get moisture in them and can cause expansion damage— all without the rebar itself ever rusting or "failing".
- Maybe so, OP mentioned they were very similar and that still seems to hold for stainless. How about the aggregates within? The composite makeup can result in different CoTE than the individual aggregates, I think that's one part of concrete sidewalks cracking though, sometimes near shaded/unshaded boundaries.
- > but that is more costly and and less efficient.
Maybe this is the clue as to why our concrete crumbles after 100 years: it's not economically efficient to make it last longer?
- A broader view of this point would be "the economic structures in some countries do not allow for investments with a long payback".
- Or simpler: people don't exactly want a house layout that was popular 100 years ago. And definitely not the level of insulation it provided. Nor the fact putting any new wiring and piping thru concrete is PITA
Tastes change and so do other requirements.
but, if we actually built for longevity in use, we could build a very durable shell of a house and then use more perishable but easier to modify methods for inside. Build a nice durable brick and concrete shell then use wood and plasterboard for room walls and floors
- There are some downsides, but most people on the UK would prefer houses that were 100+ years old. In the village I live in the houses immediately around me are "only" 50 years old. Most of the ones on the main street are well over 100 years old.
Housing tastes don't really change that much. Yes over the years we've had to fit things like double glazing and better insulation but that's a whole lot cheaper (and better for the environment) than building a whole new building.
- Having been around enough houses (in the US) to have a balanced opinion - I personally prefer older houses but
- older houses tend to be a lot more inefficient in their use of square footage
- the rooms inside tend to be a lot less open, and one man's "fun/quirky layout" is another man's "why do I have to go down a step then immediately go up a step to cross a hallway"
- and, I begrudgingly admit (as I don't like how they wreck house aesthetics) people really like big, attached garages
My overall suspicion is that when a lot of people say they like old houses, what they really mean is that they like buildings that look beautiful on the outside and, to a lesser extent, have a sense of being rooted in some kind of context.
- Cupboards, nooks and crannies are one of the things people like in an old house. They are often a side-effect of chimney and fireplace construction. A new house in the UK has nowhere to put anything!
- > but most people on the UK would prefer houses that were 100+ years old.
Why do most people prefer older houses?
- I think two reasons:
Character and history - they tend to be more individual and different, and have more character than the cookie cutter modern mass builds.
Solidity - they tend to be more stone and brick, instead of the timber framed buildings that are more common in new builds.
- Primairly because old houses are on bigger plots and allow for extensions and conversions.
- ah interesting! That's quite different from the areas I've lived in the US. If you're in or near city lines the lots on older houses are small. It's not uncommon to see .15 acre lots. Newer houses aren't much better, but you can see .2 to .25 acres relatively commonly, though those are nearly always on the outer city or outside city lines so it could just be proximity to the city that's the factor there rather than age.
- That is highly location dependent. Many cities had/have large lots in older neighborhoods and have transitioned to zero-lot-line construction or smaller lots in the past 30-40 years as demand for housing grew.
In fact in most of the western US that’s the norm…
- The UKs green belt laws haven't helped here. Since you can't make the settlement bigger, the only course is to build in the gardens of houses with big gardens. In my view it has ruined many nice villages
- I think there might be some survivorship bias there - the house that survived 100 years in state where people still want it probably was built well, the 100 years old ones that didn't were scrapped/rebuilt
- In my area of the UK at least, the house layouts of houses built last year aren't appreciably different from those built 200 years ago. That's specifically comparing detached and semi-detached houses. Terraces are a bit different now.
> then use wood and plasterboard for room walls and floor
One of the things I LIKE about older houses is that the interior walls are more solid than plasterboard. There is zero plasterboard in my house and brick gives far better noise insulation than anything timber framed.
- Well, better than most timber frames. If you were to ask for a truly soundproof wall you are likely to get a timber frame in two layers with rockwool fill and double thickness plasterboard.
It was also common to build lathe and plaster covered interior partitions in the past. Way before plasterboard.
A modern one off house may well have concrete block downstairs walls to hold the floor up. Albeit, they may get covered with plasterboard 'dabbed on' anyway, to reduce drying time
- I’m passing my latrine down to our great grandchildren.
- You don't really own a latrine, but just look for it for the next generation.
- A lot of the reason why concrete structures have failed so quickly is that the material was still fairly new when most of the structures failing now were created. There’s nothing that says that well designed and constructed modern high performance polymer modified concretes will have the same problems. They also have additives like zypex paste that make it more waterproof and self healing. They also have permeable formwork liners for increasing the surface density of the concrete and chemical concrete hardeners etc.
- "A lot of the reason why concrete structures have failed so quickly is that the material was still fairly new when most of the structures failing now were created."
Or the designer can get too creative :
https://edition.cnn.com/2025/05/15/style/432-park-avenue-sky...
- Modern concrete has steel rebar, which is very useful, but eventually corrodes. Stainless steel rebar could be used if longevity mattered, but usually it doesn’t because the building will likely become functionally obsolete and need replacing before then.
- It only corrodes if it's not completely encased in concrete. The concrete stops the reaction. And, if one portion of the rebar is not encased it will eventually corrode through overtime.
- This is something I wasn't aware of that is fascinating. The ph balance of the rebar's environment determines the progression of oxidation. There was a guy in the 1920's who observed this and had the idea to put cement in paint; it was so successful he renamed the company to cement spelled backwards.
https://www.sciencedirect.com/science/article/pii/S095006182...Inside the concrete, Ca(OH)₂, which is generated by the hydration of cement, creates a strongly alkaline environment, with a pH value of more than 12.7. In this environment, a passivation film forms on the surface of the rebar to prevent corrosion. However, the pH of the concrete decreases as micro-cracks develops and chloride from the outside infiltrates the rebar. Eventually, as the environment inside the concrete becomes neutralized, the corrosion of the rebar accelerates, which reduces the overall durability and stability of the reinforced concrete structure.
https://tnemec.com/about/A sighting of preserved steel reinforcing bars sticking out of old concrete rubble piqued the curiosity of our company founder, Albert C. Bean, Sr. After investigating this finding, his company, Armor Oil & Chemical Company, began producing a patented cement-filled coating formulation that, in its updated form, still protects structures from corrosion today.
- You could wouldnt even need that. https://de.wikipedia.org/wiki/Opferanode
- Yes, but you have to replace the sacrificial anode every so often.
- Like the plate of food on the grass for the bees at the barbecue
- More for the wasps, I guess?
- Wait, does this actually work?
- Just wish I could claim credit. Decoy plate is essential.
And since nobody complained it sounds wasteful, I suppose it should be able to be just scraps.
May your next camping trip or picnic be wasp free!
- It sure attracts the wasps. Whether you have less of them on your real food compared to the counterfactual, I don't know.
- Define functionally obsolete.
Ultimately most tall structures as a reinforced concrete skeleton with glass hung on the sides.
It seems to me that as you're going to replace it with another basically identical concrete skeleton it makes sense to have that skeleton last as long as possible. And then refit that skeleton.
- > Stainless steel rebar could be used
There are also coated and non-metallic rebars.
- Coated rebar could be good, but the coating can be damaged anywhere from manufacture to installation.
- Yup, every alternative rebar has drawbacks which causes increased costs or different failure modes which is why they tend to be used in specialised applications where they are necessary.
- Related, Grady Hillhouse on the myth of Roman concrete.
> The miracle of modern chemistry has given us a wide variety of admixtures like superplasticizers to improve the characteristics of concrete beyond a Roman engineer’s wildest dreams. So why does it seem that our concrete doesn’t last nearly as long as it should? It’s a complicated question, but one answer is economics. There’s a famous quote that says “Anyone can design a bridge that stands. It takes an engineer to build one that barely stands.” Just like the sculptors job is to chip away all the parts of the marble that don’t look like the subject, a structural engineer’s job is to take away all the extraneous parts of a structure that aren’t necessary to meet the design requirements. And lifespan is just one of the many criteria engineers must consider when designing concrete structures. Most infrastructure is paid for by taxes, and the cost of building to Roman standards is rarely impossible, but often beyond what the public would consider reasonable.
https://practical.engineering/blog/2019/3/9/was-roman-concre...
A large part of why Roman concrete lasted longer than ours tends to is that we suffer from a shortage of narcissistic emperors with the means to wield entire economies towards their own immortality.
- This is a good link and the Practical Engineering guy doesn’t appear to reference a “myth.” Which is a good thing, because there’s nothing mythological about the high performance of Roman concrete.
- The myth is that Roman concrete was 'better' and that we don't know how to recreate it. The facts are that it was not better in any way than what we can do now and we have always known how to replicate it. Grady addresses both of those aspects of the myth in the video, and the first part is literally the title of the video: "Was Roman Concrete Better?"
The answer is no. What is true is that some Roman concrete structures (but far from all of them) are extremely durable because they were optimized for a different set of requirements than modern buildings usually have, notably "needs to last forever as a symbol of the emperor's power". From the 19th century on that has very rarely been a design constraint, so we optimize for other things instead.
- Most infrastructure is paid for by taxes, and the cost of building to Roman standards is rarely impossible, but often beyond what the public would consider reasonable.
Would you pay 10x more to have something that lasts 100x or even 1000x longer? The upfront cost is higher, but the TCO is ultimately lower. IMHO it's ultimately a form of planned obsolescence. This becomes even more obvious when plenty of expense is spent just on "engineering" to deliberately reduce lifespan.
- No, for two reasons.
First, we can’t summon infinite money to pay for things. Paying 10X more per bridge means we can build 1/10th as many bridges or we have to start stealing from other budgets.
Second, we don’t know what the needs will be for the bridge in that location 100 or 1000 years from now. It could need to be torn down to be widened. Maybe we’re all riding around in electric vehicles that coordinate perfectly with each other and the bridge isn’t needed for cross traffic any more. We don’t know.
- You don't have to wait 100 years. You can build a bridge to alleviate traffic without any understanding that the bridge will in fact generate more traffic, and then you have to widen it a few years later (which also doesn't help). I know this has happened several times in NYC and I'm sure it has happened many other places where engineering know-how far outstrips knowledge of urban planning.
- On the other hand having 10 times as many bridges could prove to be an impossibility when maintenance costs come knocking.
- Well, invading a few fewer countries could pay for a few longer lasting bridges … it’s a matter of priorities.
- No, because there are public projects that make sense at 3–4% discount rates that haven't been funded, so it would clearly make more sense to direct funding towards those projects first before trying to fund anything that requires a sub-1% discount rate.
- The thing is, we're actually pretty crappy at knowing what we'll need 50 years from now, much less 500. Doesn't make sense to overbuild for an unknown future, when hundred years from now us will likely be able to do a far better job anyway.
- That's to consider the commons solely materialist utility. The Romans built meaning through arts that still speaks to this day. Efficient construction becomes worthless over time.
- Yes, you, too, can have two-thousand-year-old buildings if you're willing to make that longevity be the primary thing you pay for, assuming that your successors don't tear the thing down and replace it with something else, like happened to many Roman monuments.
In which case you spent a bunch more than you needed to on a building that didn't last any longer than it would have if you'd chosen a practical end date for it.
- Efficiency is never worthless in a world where resources (if nothing else, labor) are not infinite.
- The kind of efficiency we focus on seem to be plentiful. Labour is a good example, see unemployment rates and the number of bullshit jobs anyway.
What's covered in the article is also a great example of material resource that could be used, but short term profiting primes.
- The same is said for why we don't build classical buildings anymore and trend towards more featureless stuff... and it's also mostly bullshit with plenty of counterexamples.
Truth is it's often just a bit cheaper so we trend that way under capitalism, we change styles faster and have come to subconsciously accept shorter lifespans and the kind of things you can build more practical for cars, large overhangs, etc
- But it's also true that modern world changes much faster than in the antiquity. If you built a church, a market, and a few utility buildings like tavern and blacksmith in 500BC you could rest assured they'd still remain used in 1000 years practically unchanged unless the structure or wider economy collapsed. Meanwhile "office building, shopping mall, nightclub, school" all varied highly in popularity within last 50 years, and it's difficult to convert one type of building to another, not to mention the costs of modernizing an old building.
- Well also building cheaper makes converting such structures to other uses more costly too. You can't simply start notching steel and adding more features and beams without a complicated engineering review because those beam were so carefully designed as to just barely hold up under their original plan.
You can't simply add a second story to a mall or walmart or modern school, none of its main structural pillars or beams could hold it. But with an overbuilt structure from 500+ years ago you likely could add another floor or two with minimal improvements to the base structure.
- > we suffer from a shortage of narcissistic emperors
not recently
- but not ones willing to put the effort into properly fixing a pond.
- If you're talking about the algae, it came back after Obama's $34m renovation, too.
Turns out algae is hard to kill, especially when you feed the reflecting pool from a tidal basin.
- I don't remember Obama pretending it was being caused by political agitators, etc.
- Who's pond? I'm willing to bet billionaires' estates have well tended ponds, contrary to public ponds. Or a reflecting pool.
- The whole promise of engineering is not to build a bridge that stands but to build a bridge that barely stands. It is not a good idea to build a bridge that last 500 years. You likely destroyed valuable resources to build one. Build a bridge that lasts 100 years and save those resources. In 100 years the technology to build bridges improves so much that it is lot easier to build a new one. At least in most countries like India.
- >It is not a good idea to build a bridge that last 500 years.
Why not? A well-build bridge from 500 years ago is perfectly functional today [1]
- > In 100 years the technology to build bridges improves so much that it is lot easier to build a new one
This hasn't even been true for 200 years lol
- We don't build better bridges than we did 200 years ago? Forgive me if I'm wrong, but it seems like we build bridges right now that would have been unthinkable 200 years ago
- Nobody is going to tear down old bridges and rebuild them at enormous costs just because technology changed. Some things can't or won't be redone and so it's worth it to build it to last and getting it right on the first try.
- This is exactly what we did with houses, buildings. We had perfectly functional 100+ years old fully functional, gorgeous buildings and we replaced those with brutalist concrete/glass barely functional garbage.
- In Europe we have plenty of old buildings. The good ones (i.e. made by very wealthy people) tend to be decent, with a skew towards huge living rooms but tiny rooms. The cheaper ones are a mess to mantain: cold in winter, hot in summer, expensive to renovate (it could be more expensive to renovate than to build a new one), bad to no isolation, in my region terribly humid, usually too dark with minuscule windows for modern standards.
With roman buildings that last 2000 thousand years we are looking at survivor bias. Near me there are some roman ruins from a (cheap and small) public bath that are barely distiguishable from a pile of bricks. The are some nearby pre-roman ruins in better shape.
- >cold in winter >in my region terribly humid
You need to actually reduce draft a bit (often old houses like mine tend to accumulate flaws that the elderly living there before didn't fix anymore.) and use a heating sources that matches.
Having a fireplace is fine. It could overheat the house whilst also keeping air dryer and it's essentially renewable (compared to the alternatives and houses made of more plastic insulation than anything else) if you don't mind air quality dip in winter.
That said i can see how that's no longer an option in places that have drastically increased their population
- Fireplace is extremely inefficient, and really bad for both your (exhaust fumes get into the room anyway), and your neighbors (the smoke doesn't just dissappear) health, though.
I love the heat and smell of a good fire as much as the next guy, I'm just not sure it's worth the risk of cancer and respiratory diseases.
- If efficiency is important, like if you are using wood for primary heat, you should at a minimum be using a sealed box stove which should be pretty efficient and have little to no smoke escaping.
Alternatly you could just use an outdoor stove that merely heat exchanges to the inside.
- There are exactly 3 old buildings in Warsaw thanks to the Germans. Brutalism exists because a generation who grew up in rubble wanted solidity.
- They weren't torn down because there was better technology available. They were torn down because they were falling apart, or were no longer meeting the needs in that location. I love old buildings – my house is 250 years old – but there's no denying that generally they are less suited to current needs than newer buildings.
- Older buildings are generally more flexible though.
In the UK, within living memory electricity has become widely available, TV has, gas, internet etc etc. and yet we still build houses without the assumption that some cable isn't going to be modified in the wall some how.
There's fairly modern houses that didnt have the 2 courses of brick added to the loft to allow 300mm of insulation to be installed.
We are now building houses with gas boilers, knowing that they will have to be swapped out probably before the life of the boiler runs out. And I bet the radiators and piping aren't sized to make that possible. That the circuit isn't sized for that.
Yes none of this is easier in a 250 year old house, but it isn't harder and 250 year old houses hadn't really changed appreciably for a few centuries so it isn't as if there would be an expectation that you would be installing new things in the wall every decade.
- Those are houses though, private property. Not government infrastructure.
- Usually you need wider bridges, so the old bridge needs a replacement or a second bridge on the side.
- If the bridge became a bottleneck, then there is an actual reason to replace it. People aren't doing it on a whim because technology changed.
- But we are currently doing it when a bridge can't handle modern traffic levels because it was designed thinking in 50's traffic (single lane for each direction without peatón or bicycle ways to 4 or 6 lanes and pedestrian and bicycle ways).
- Modern concrete includes plastic fibers like polypropylene, fly ash (a great source of arsenic, lead, and mercury), silica fume, formaldehyde, and often even PFAS
This type of concrete does not give us any more flexibility in the future to rebuild or upgrade because doing anything to it could turn it into an environmental and public health hazard
- Aren't structures like bridges tested to at least 1.5x design parameters? In our field it's usually 2x (pressure and lifting lug strength).
- Sometimes knowledge gets lost and newer doesn’t automatically mean better
- In fact, the dominance of concrete is surprisingly political. It has a lot to do with Cold War geopolitics
https://www.listennotes.com/podcasts/the-conversation/keepin...
- Case in point, Roman concrete
- Very interestin discussion below/above. I just want to say that building with hempcrete, which relies on lime and NHL (natural hydraulic lime) or Baumit Trassitplus whic is some version of roman "cement" relies on may of these principles and is a "modern building technique". It's also much more carbon neutral than many other methods, can produce good thermal dynamics and "breathable" walls. And is DIY friendly.
- Compared to traditional concrete, isn't hempcrete much weaker and less rigid? It's an interesting material for sure, but I thought it was basically considered non-structural filler.
Autoclaved aerated concrete is worth a mention as well - it's also a decent insulator and somewhat environmentally friendly, while additionally being, light, easy to cut, and somewhat usable as a structural element.
- A picture of one of these toilets would have been useful.
- I am glad the pantheon still stands. But the real question is are there really any modern structure that will be worth preserving for 2000 years. Architects have long abandoned aiming for beauty to aim for originality. Originality doesn’t last. Humans in 2000 years will only wonder why on earth our society could manufacture atom level micro ships but couldn’t come with a single structure worth preserving.
- All structures are worth preserving. The article is about a latrine. Do you think ancient Romans thought a literal shithole was worth preserving? And yet, it is now an important piece of history.
As for beauty, you never know, take the Eiffel tower for instance, when it was built, people found it ugly, and it was to be a temporary structure. Now it is the symbol of Paris, more popular than the Paris Pantheon, which much better fits the classical standards of beauty.
The Eiffel tower is also more historically significant, more representative of its time. The Paris Pantheon, is an imitation of the Roman style, beautiful, but probably not as interesting for future historians. If both building survive that is, which won't happen without continuous maintenance, at least for the Eiffel tower.
- The Eiffel Tower dates from the XIX century. Pre the shift to originality. Which XX century building in Paris is objectively beautiful? The tour Montparnasse? The Centre Pompidou? Or Jussieu’s campus? Even the Opera Bastille is pretty lame, not outright ugly but lame.
- I like Centre Pompidou, and if it wasn't technically problematic, it could have aged really well.
For those who don't know, Centre Pompidou is built "inside out", with all the technical parts like ducts, framing, elevators, etc... fully visible from the outside. There is some beauty from function here, like looking at an old locomotive. For people in the future, it would be an insight into what a 20th century building is made of.
Problem is: for a form-from-function design it is not very functional. Because the technical parts are also part of the aesthetics, it makes maintenance problematic. Every single pipe you change has to be of the same model or you would ruin the façade, which is crazy. Unfortunately (for me), it is one of the least likely building to stand the test of time, from a technical perspective.
Other than that, the Louvres pyramid is starting to gain some acceptance, even though it was almost universally hated when it was built, who knows how it will be seen a few hundred years from now, if it still stands.
- There are some structures worth preserving. Sagrada Família is one. Places of worship and private homes (at least those individually architect designed vs standard designs) tend to be a lot nicer than office blocks and other commercial places.
I do think a lot of new building hideous. Looking at St Paul's in London from the west so you see the hideous backdrop to its east is depressing.
- Sand used to make concrete is a finite ressource, and extremely polluting to extract. Why wouldn't we save it and build lasting buildings?
- It is not.
You can make sand by crushing rock, we don't because it is cheaper to extract natural sand. Should we run out of suitable natural sand, we will just have to go with the more expensive option, not a big deal.
- What makes you think buildings aren't going to change within the next 2000 years? Hell just look at all of the Tudor buildings dotted around. They probably didn't think they were anything special 600 years ago
- Is anyone else wondering why their house isn’t made of Roman Concrete everytime they read a story like this.
- Nobody wants to pay for a house that would take a year to build, with multiple 30 day work stoppages for concrete curing….
- Survivorship bias? The only Roman Concrete we see today is the stuff that has lasted.
- There must be a better format and distribution method than this. Ideologically a strong brand name and domain, yet ads every two sentences. Even with ad blocking, there is constant aggressive attempts at attention.
I propose the communal brain rot is less to do with short form video, and more to do with the everyday experience of trying to read something enlightening, tickle your curiosity - and be just absolutely fucking hammered with autoplay interstitials and 720x90 and 300x250 bullshit.
- There is, the article links to a source, https://www.scientificamerican.com/article/how-a-1-900-year-..., which you need a $5/month subscription for.
I'm sure hidden in the links is a link to the paper, which you can pay to get the no-nonsense study.
This is the third or fourth degree of scientific reporting; first is the paper, second is a news report, third is adult pop sci magazines, fourth is youth pop sci magazines. Pick your poison / preference.
- Do you pay for satisfy your curiosity?
In fact, that institution is non profit and publicly funded, so what gives...
Anyhow reading the piece with Brave showed me no ads whatsoever.
- How do we know Egyptian pyramids were not build from a form of concrete?
- Because they are solid stone carved from the mountains south of Cairo, near modern day Helwan.
- Yet carbonation is not universally helpful
- Nothing is universally helpful in the most extreme hypothetical.
- Thinking of the ww2 plane with holes meme right now.
- Imagine how it'd be if BigConcrete were to make concrete. Every year at ConcreteCon, yet another release that lasts for... one year!
- A lot of comments here on Roman concrete are missing the killer application: marine use. Any other concrete we know of will degrade in seawater due to different failure modes acting at once (leaching minerals, pH imbalance, freeze-thaw cycles), and none have the same extent of self-healing.
Roman concrete (pozollanic material, quicklime, seawater) is the only one that resists all failure modes and will sit in the ocean happily for millennia. The main downsides are it's not very strong, it takes a long time to cure, and volcanic ash is hard to come by. The specific of ash you use changes the result, ash is not always that easy to get, and Neapolitan Volcanic ash just happens to be extremely effective at this application.
There are alternatives you can make today. You can make Roman concrete today, but it's still kind of tricky and has the aforementioned downsides. Fly-ash concrete is like volcanic ash concrete but still not as good, and we're gonna run out of fly-ash as coal mines close. High-slag concrete works well but will degrade over time. Alkali-activated concrete is really promising as a Roman concrete alternative but doesn't have long-term test data. Ultra-high-performance concrete is brittle and won't self-heal.
So in truth we still don't know everything about Roman concrete and we still can't make its equivalent without traveling to southern Italy.
- we can't figure out roman concrete
we don't know how ancient megaliths were built
centuries old cathedrals and holy places have more intricate masonry and carvings than anything built today (with allegedly more primitive tech)
are historians retarded? what's going on here? time is flowing backwards and civilization is declining, but humanity is under a collective trance and can't even see it.
- > time is flowing backwards and civilization is declining
Why do you think civilization is declining?
- I’ve often wondered why every good sidewalk I see has a WPA stamp on it from the 1930s and the modern ones are all crumbled and uneven.
- Don't you love it when gemini quotes an AI generated video with 83 views as a source of truth
- I'm also judging by my own eyes because I can see that the WPA concrete uses coarser substrate like the Gemini answer says and is harder than normal concrete when I press it. And also has no cracks in it almost 100 years later.
- .. and, also, ...
The folk of the 1930s were entirely capable of making poor quality concrete that barely lasted 30 years (source, my father, born 1935, still alive despite having mixed many a batch of concrete and having laboured).
The reason you don't see that walking about is that poor quality 1930s concrete was replace 50+ years ago.
- Survivorship bias in action.
- I don't see how this would work because you're saying that the older sidewalks are scrapped and rebuilt when they hit a state of 'x' deterioration, so you only see > 'x' state ones. But how then could it be that newer sidewalks are allowed to fall below 'x' instead of also just being scrapped and rebuilt?
- Municipal budgets cratered hard over the past couple decades, roadway maintenance is given precedence over sidewalk maintenance, and SUVs and electric vehicles do considerably more roadway damage per vehicle. So there’s concurrent causes promoting a global decay in sidewalk maintenance in cities that expanded without the necessary tax base to support maintenance: see for example Los Angeles (current-day example!) repaving all but one foot’s width of their roadways so that they don’t have to fix broken sidewalks. This doesn’t contradict the survivor bias point! If anything, it’ll accelerate it: you’re about to see just how many (or few) sidewalk squares survive the underspend. Citizen science, here we come!
- Politics, money allocation, taxation, etc. The US had a golden age last century and is now in decline. It can still bounce back but it needs a political and legal revolution, in this particular case, it needs to tax the wealthy and spend it on municipal improvements.
But that's socialism / liberalism and apparently that's terrorism now.
- This is a bit of a tangent, but government revenue has skyrocketed in recent decades. Here is an inflation adjusted table. [1] As a percent of GDP it's been fairly stable since the end of WW2 [2], and dramatically higher than prior. But that understates reality because it excludes deficit spending which has increased exponentially since then. So the government is collecting and spending substantially more than back in the golden age, even after accounting for population/economic/etc growth.
[1] - https://usafacts.org/answers/how-much-does-the-us-federal-go...
- Gemini 3 Flash?
Edit: if you were an expert in this field and that link saved you from typing, and you mentioned you could confirm every word, that’d make sense - I think those Flash models were tested as being as reliable as a coin flip in some hallucination test scenarios, so linking it’s like… eh do I wanna read potentially-only-plausible history?
- This is truly a great miracle
- corrosion of rebar is so significant that there are specs for the acidity of rock used for agregate in the concrete. Older rock that has been "washed" by billions of years of water permiating it , is then used, fetching a premium. Look into it and there are periability numbers for everything, which is how water has gained it's reputation as the universal solven, and granite, hard as it is, is also a bit of a sponge. What is harder to figure is the use of a lot of carbon in rebar, which makes it harder and with a higher tensile stength, but with greater rates of corrosion, somehow the calculation is to not use an ultra low carbon steel with some nickle and larger cross sections along with low acid chemistry in the concrete.
252 points by divbzero 16 hours ago | 207 comments
