Interview with Paul Jaquin!

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 Spain, built probably by the Knights Templar and expanded over the years. It is still inhabited, but there are sections of the building which are decaying. The main problem is one of the front façades, which appears to be coming away from the rest of the building because of failure of the foundations. I spent a week studying the building, constructed a reasonable computer model of it and tried to establish what was going on. Looking back I feel the work wasn’t too great, but I certainly got a taste for old rammed earth. There are pictures and a bit more information at
http://www.dur.ac.uk/p.a.jaquin/Past_projects.htm

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 Spain. The plaque on the door (original) says it was built in 967, which makes it 1039 years old! I know parts of the Alcazaba in Granada are older (built in 852) but they are really well hidden, and I'm reliably informed that parts of a site at Merv in Turkmenistan are probably over 2000 years old, but the castle at Banos is the oldest I've seen. The newest rammed earth is a 7m high wall at Aykley Heads in Durham, which has recently been finished as an internal wall on a sustainable office complex. The differences between the two are quite marked, the main ones being that the old rammed earth is much more like concrete, there is a high proportion of lime in the mixture, and it is much more solid to the touch, it is impossible to get anything from the wall. The modern rammed earth is much more friable and probably less hard wearing. The other main difference is in the formwork, historic rammed earth uses crawling formwork, which leaves characteristic holes through the full thickness of the wall, whereas the modern practice is for concrete type formwork which is supported from the ground and so leaves no marks on the wall.

3. Could you tell us more about the wall at Aykley Heads in Durham? Specifically, could you tell us about the material used, the compressive strength, the form work, the footing, the rebar and the kind and amount of stabilizer (was it cement?) used?

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 (Durham is quite a wet place!). Its also non load bearing, so it is just about alright to not use rebar and cement. Also the contractor is also the client – they are building themselves new offices - and so are willing to experiment with new materials, they are hoping to make a name for themselves in the UK rammed earth industry. The formwork turned out to be the most expensive part of the project, concrete formwork was used and the cost of hiring of that sent the costs soaring. As for the compressive strength, I'm not sure really, I know some samples were tested during testing of the materials, but I'm not sure what they were. I tested some cubes constructed from the same material and got strengths around 1MPa.

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 Granada had compressive strengths of around 1MPa. You only need rebar really to provide tensile and shear strength in the rammed earth. The structure is pretty much all in compression, and the walls are around 1.5m (i guess about 5ft) thick so there isn’t a problem with wind loading because of the high mass of the walls. This area of Spain isn’t particularly known for earthquakes (except a big one in Lisbon in the 1700s) so ground movement isn’t a problem either. The face was initially rendered, probably a number of times, there is evidence of different coats of render on the outside. Most of that render is gone, but the wall seems fine underneath.

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
http://www.castillosnet.org/jaen/J-CAS-007A1.shtml and
http://www.dur.ac.uk/p.a.jaquin/spain_rammed_earth.htm#banos, but
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 Himalayas which has survived since 1600. There the temperatures get down to -20 or -30 degrees Centigrade (-4 to -22 Fahrenheit) with permanent snow. I've not checked out the buildings during the winter, but I'll hopefully be visiting some this November, to see how they hold up in the cold. I believe that quite a lot of the buildings on the Silk road route are rammed earth (Kazakhstan, Tibet etc) which also experience low temperatures, but I guess here the temperature is cold during the winter, but hot during the summer, so the buildings are probably built in the summer. I also get the impression rammed earth is taking off in the Vancouver area, but I guess they have similar temperature ranges to Tibet. It is also found in China at the Yellow river Delta, I'm not sure of the temperature there, but the latitude is the same as New York.

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 UK, India and Spain, probably coming to about 70 different sites. I still think my favourite is the castle at Banos as I mentioned earlier, its 100% rammed earth, and over 1000 years old, all the crenellations on top are rammed earth and are still intact. It has a really interesting history, at the moment archaeologists are excavating the inside of the castle because it was used as a graveyard until 1900. The best thing is that you have to ask in the village for the key and then you can just go and wander around.

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 South America constructed in rammed earth are done using the same methods used by the Spaniards in the 16th century, they just shipped the technique across the Atlantic. Likewise when Cointeraux rediscovered rammed earth in the late 18th century, he got copied and rammed earth from around that period is all pretty similar. I must admit I love the old stuff, but I think that’s because it has been there the longest, and I think the level of knowledge and expertise in rammed earth construction steadily decreased over time as newer materials came along.


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 UK? Is it a 'mainstream' building method or is it seen as 'exotica?'

In the UK its not massively well known- there are some earthen buildings in southern England, called Cob, but there is no traditional rammed earth. There have been a few projects in the past probably 10 years, each with varying degrees of success. However it is certainly becoming more popular amongst architects, who are keen to specify rammed earth as an exotic and sustainable technique, but I would say that nearly all of the projects taking off in rammed earth are using it as an exotic material rather than as the 'best' material for the job. I don’t think rammed earth in the UK will ever become a mainstream building material in the UK, because of the high labour costs involved, and the fact that it doesn’t really bring any benefit to a building, we don’t have the high external temperatures to contend with, and it has to really prove itself in the relatively humid UK environment. Having said that the UK market is trying, we have no national standards for rammed earth construction, but a recent publication "Rammed earth: design and construction guidelines" is hopefully the first step to a full UK standard.

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 Spain in October where I should be able to check out quite a few more historic rammed earth sites. I've also got a university expedition in Morocco at the moment checking out historic and modern rammed earth there. I'm then presenting at a conference in Delhi in November, and I should be able to get up to northern India to look at some of the historic rammed earth there too. I'll then be in the final year of my PhD and should be able to properly analyze and draw some conclusions about how rammed earth actually works, and the ways it decays, and thus the best ways to protect it and to repair it.

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!