Why was Roman Concrete Forgotten during the Middle Ages?

David Trammel's picture

One of the mythical mysteries of history is why after the Fall of the Roman Empire was the useful technique of building with concrete forgotten? This video answers some of that.

"Why was Roman Concrete Forgotten during the Middle Ages?"

Why is that important for Green Wizards, and in particular Green Wizards who write? With Greer's theory that we will be seeing a slow decrease in available technology and a new Dark Age in the next few centuries, ask yourself "What modern technology will the people of the future forget?" That answer can give you story ideas.

The short answer from the video is that the technique wasn't really lost but abandoned because the huge buildings that concrete was suited for stopped being built. The needs of the population and the tastes of the monied patrons who financed the construction changed. Huge stadiums that need electrical lighting and climate control will fall to the wayside in favor of older open-air stadiums which are used on good weather days only. The monsters of the current time, which are as much a product of ego and self-aggrandizement as they are of modern construction techniques will disappear for those kinds of buildings that use less.

One thing I found interesting, is the way that early Roman foundations were built, not with pouring concrete as we do now but as shallow layers. An exterior mold of bricks or cut stones was made and supported, then a layer of broken tile or stone was put in and the gaps filled with a slurry of mixed mortar. This was tamped down with wooden paddles. Once dried most of the way, another layer was put down. Given all the current concrete structures, I could see this kind of re-use becoming popular as a way to cut costs. As future Ruinmen, disassemble old buildings for their metals, the remaining concrete rubble will just sit there looking for use.

What do you think? What things will we forget?

Ken's picture

I worked pouring residential foundations for about a year and a half straight in my late 20's. In so doing, I got to know way more than I ever wanted to about the stuff. One problematic fact, very likely the same problem that the Romans ran into in the declining years of the Western Empire, is that hydraulic cement (aka Portland cement) is extremely energy intensive to produce. Water, gravel and sand are everywhere but the precise formula for cement is not easily reproduced outside of a few geographically fortunate (or unfortunate, depending on your point of view) areas. If my memory serves, the western Untied States for example, was without a local source for cement until sometime in the late 19th century. Clearly we will want to know how to make decent mortar in the coming years, although everything from mud to cow dung has been successfully used in various places. So, I agree that having knowledge of the surprisingly complex process of making cement widely known and practiced would probably be a good thing for the coming low-tech millennia.

From a general ecological point of view, I don't care for the centralized aspect of concrete batch plants, nor the massive CO2 emissions produced by the process and industry.

From a personal aesthetic point of view, I don't like working with the stuff nor do I care for the way that concrete products look, especially as they age. For now, it's a relatively cheap and fast way to build things, but like most of our culture's cheap and fast practices, it is extremely wasteful and frequently results in hideously ugly structures. As long as I can get a little mortar for grouting tile, I'm good with no more concrete structures!

Utah is dotted with pioneer lime kilns where settlers burned limestone to make lime for mortar. I am sure brick kilns were not far behind, so the lime was needed for mortar. I suspect that if we lost the ability to make cement, we could at least make lime.

Ken's picture

Agreed. Lime kilns fired with the old growth forests of the Pacific North West produce prodigious quantities of lime. The islands of the Salish Sea are dotted with lime kilns. NONE of which are functional now. But Seattle has lots of concrete doesn't it?

mountainmoma's picture

I live in the mountains by lime kilns, old and new. California. Cement and lumber from here rebuilt san francisco after the great earthquake.

The modern lime kiln, the cement plant only ceased operating in the last 10 years. I believe we still have plenty of of feedstock on this mountain. I think It was shut down due to the normal reasons of predatory buyout. It was bought out by a large international conglomerate that ran it breifly, a few years, then shut it down and sold off all the land. There was an extremely large amount of land, good forest, that was the property associated with that cement plant.

mountainmoma's picture

making lime cement is easy, not hard to reproduce. You get some limestone or marble or shells and heat up VERY hot to make lime. Powder the lime. Slake it with water. Add sand and gravel.

I have done this small scale when I homeschooled my daughter, along with field trip to hike out to some of the historical kilns and the cement plant

She did a mosaic decoration on the outside of a clay flowerpot using the mix and a few decorative things

lime concrete is great for building with in general, it takes longer to cure and I believe it does not set up under water. But for house foundations, we could very easily have lime concrete.

Ken's picture

Lime is indeed useful around the homestead, from mortaring tiles to nixtamalizing corn to making whitewash for the henhouse (it seeps into cracks and gaps in the wood and inhibits mites that otherwise can build up to such a point your chickens will suffer badly) or for conning your friends into whitewashing a fence for you! If you don't have coral or limestone to burn, but you do have hardwoods, it's possible to make lye by leaching wood ashes. Just be careful with any of these powerful caustics. Remember that while lye cuts grease very nicely, your cell walls are made up primarily of lipids and lye makes no distinctions between your fingers and whatever you are cleaning. Quicklime (unslaked lime) in particular is terribly dangerous to have around and doesn't store well. Slaking it yourself should only be done with appropriate caution and proper ventilation. Adding water to quicklime generates temperatures over 100°C – water boils, lots of steam given off – and there will be some quicklime in the steam, so best not to breathe it! I have always suspected that one of the material "secrets" of the mason's guilds in the middle ages was how to make lime, slake it safely, and make functional mortar. Even when I was a boy, there were old men working with my dad that claimed concrete wouldn't set up without some blood in it; there's a certain magic to the process...

mountainmoma's picture

It's realy not that bad. I have used lime many times. So I have mixed the store bought dry quick lime with water. Yes, it gives off a little heat. As far as slaking, it is said to slake it ( mix with water) and let age before use if possible, supposed to make a beter plaster. I have done that too. I mixed in an old enamaled cast iron bathtub outside, then covered with a piece of plywood to keep things from falling into it.

I have never made lye from wood ashes, but I also do use lye, mostly for soap making. It feels slippery on skin, a small amount, like a grain. Also use it in homeschool science experiments. It is very cool to mix acid and lye in the correct proportion, checked with homemade red cabbage Ph indicator and other things to do...

Ken's picture

I have often thought about the spread of the use of lime in parallel with the cultivation of maize. The corn seems to have spread first, followed by the use of lye and slaked lime to nixtamalize the corn, followed (at least as far north as the Anasazi culture) by whitewashing of mud plastered adobe or stone walls. Adobe bricks, mortared with mud (interestingly, everyone that works with mortar or concrete STILL calls it 'mud') and then thickly whitewashed, will withstand rain and wind erosion indefinitely as long as it's regularly renewed. It also is a beguiling canvas; who could resist a huge white wall? AND, just as with the frescos of Michelangelo, adding colors to semi-cured plaster is a way of producing a durable and long lasting artwork. Some of the streets in old colonial towns of Mexico still maintain a version of this (see the photo). It's no wonder that mural art is so developed in that country; centuries of practice!

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