Proprietor of Historic Rammed Earth (the website) and Historic Rammed Earth (the blog), PhD candidate Paul Jaquin has visited and studied rammed earth buildings all over the world. Here we turn the questions up to eleven. A big thanks to Paul for all his time!
1: What and where was your introduction to rammed earth? What kind of building or structure was it?
Paul Jaquin: As an undergraduate engineering student I had to come up with a one year project as a dissertation for the final year of the degree, I wasn't keen to do a standard project and approached my supervisor to see if he had any special projects. He had been approached by a member of the Archaeology department at the university, who were having issues with a structure they were studying. We devised a project centred around investigating the problems with this structure and devising ways of repairing it. The building is an 11th century fortified mansion in northern
2: What (and where) is the oldest rammed earth building you've ever seen and what (and where) is the newest? How would you describe the difference between the two? How has the medium evolved?
The oldest rammed earth I've seen still standing is at Banos de la Encina, which is a fantastic castle in southern
3. Could you tell us more about the wall at Aykley Heads in
Sure, the wall is 7m high, and in sections which are about 2m wide I think, to prevent shrinkage due to the high clay content. It’s on a concrete footing which is about 6 inches from the floor. Surprising for you guys I guess it’s not reinforced with rebar and there is no stabiliser, its full unstabilised rammed earth! However it is fully internal, and so doesn’t get any weathering on it at all (
4. Could you tell us more about the castle at Banos? Do you know about the material used? Do you have any idea of the compressive strength? What is the footing made from? How did the structure last so long without re-bar?
The material used appears to be just rammed earth, with a footing made from the same material, but which appears slightly whiter, indicating more lime was used. Interestingly the tops of the walls seem to be made from the same lime rich material as the foundations, which I think is how they are so resilient. I've no idea of the compressive strength, but I know of one set of tests performed on rammed earth cored from
I'm not massively sure of the history of the castle at Banos, it was definitely built in 967, because there is a plaque by the door, i think it was used as a castle during the Caliphate, which was up to around 1200AD, and then used by the Christians for some time before being abandoned. It was used as a graveyard from the mid 1800s until about 1920 and the centre of the castle has been filled to about 3m. But now archaeologists are excavating the site, so we shall see what that brings. There are pictures at
unfortunately the video doesn’t work yet.
5. Tell us about your PhD--What is your dissertation, what is the program like, what did you do leading up to this point and what do you hope to do once the PhD is complete?
The title of my thesis is 'Analysis of historic rammed earth construction'. I came to it straight from my undergraduate degree in civil engineering, writing a PhD proposal from information gained in my undergraduate dissertation. I found that there is a massive gap in the understanding of rammed earth (and other earthen architecture) from an engineering point of view. When compared to concrete or steel, the amount we know about the processes at play within rammed earth is pretty minimal, but there is a huge body of knowledge in geotechnical engineering. My idea is basically to take soil mechanics and apply its principles to buildings. Given that apparently one third of the world's population lives in earthen type buildings I was surprised to find that no one else is looking at this. Unfortunately as no one else is looking at this the program is fairly unstructured, its fully research led, and I'm looking at a few different avenues at the moment, hopefully all brought together in a thesis at the end.
Once I finish I feel I've got a number of options, I have to get some experience as a proper engineer really, so I might head off and do that for a few years. Alternatively I could continue research into rammed earth, I feel I'm just scratching the surface here really, but I would most like to work on some restoration projects, essentially put my PhD to good use, we'll have to see what comes up.
6. What are some of the common ways rammed earth structures "fail?"
What I've found is that the main problem is water from the top of a structure causing decay of the wall surface, and that if the top of the wall is well protected then the rest of the wall is probably going to be alright. I've heard lots of things about having overhanging eaves to prevent water hitting the base of the wall, but I've not found that walls fail in this way. I would also say there is a difference in the way historic rammed earth fails compared to modern rammed earth. The historic rammed earth has been up for hundreds of years, so failures in these buildings usually occur due to a change in conditions, for example a change in rainfall patterns, or lowering of the watertable leading to a change in ground strength, or through lack of upkeep, if the roof isn’t kept in good shape then you start to get moisture ingress which weakens the wall.
Modern rammed earth on the other hand seems to fail due to say a high clay content leading to shrinkage cracks, or too quick removal of the formwork leading to plucking of material from the face of the wall on removal of the formwork.
This is one of the main aspects of my research at the moment, so I'll probably end up writing a paper about it.
7. How does rammed earth perform in cold weather?
I think the cold isn't really an issue, it has much more to do with moisture. I know that there is rammed earth in Ladakh at 3500m in the
8. From the looks of your site, you've seen quite a bit of rammed earth. Do you have a favorite building? Do you have a favorite rammed earth 'vernacular'? Are you partial to any one culture's 'take' on rammed earth?
I've certainly seen a lot of rammed earth, up close I've visited sites in the
The main thing I think I've found is that rammed earth is pretty similar where ever you go in the world, and varies much more in time than in space. Most of the buildings I'm looking at in Spain were built during the Caliphate, when Spain (and quite a lot of the rest of the world) was ruled from Damascus, so you find exactly the same techniques in Spain as you do in Morocco and India, which I find really interesting, I guess there are only so many ways to ram earth between boards. Even many of the buildings in
9. Have you ever built with rammed earth? If you have, could you tell us about that experience?
I've built 6 test walls in the laboratory. fairly small affairs but enough to give me an idea of what is going on in rammed earth. We used an unstabilised mix, and compacted using a Kango electric hammer, rather than compressed air. Once I had done two walls I think I got the technique sorted out, compacting at the right moisture content, and allowing the walls the right amount of time to dry. When I tested them I was interested to find that there was failure along the compaction planes as well as cracking under the loading ram, I wonder if anyone else has had experience with rammed earth failures in real buildings?
10. How do people perceive rammed earth in the
11. What's coming up on your rammed earth horizon?
Well at the moment I'm just starting in the laboratory on testing some cylinders and trying to explain their compressive strength based on some new soil mechanics theory. Following that I have another field visit to northern
Following the PhD I'm not sure, I would like to write a book about historic rammed earth, and maybe a manual on its repair, but that is certainly for the future, we'll have to see what happens!