Rammed earth formwork
Rammed earth formwork
Rammed earth is an age-old building technique used in many, many parts of the world. It is similar to cob and adobe insofar as the idea is to build using the materials available on site, however rammed earth is made using much less water in the mix, the initial shape being built in temporary shuttering or formwork, with layers of the mix rammed into place with hand or power tools. Rammed earth also uses no extra binding material such as straw. In many countries where rammed earth is used insects like termites mean any organic material in the mix could be an issue. Another environmental plus is that rammed earth absolutely does not need cement added (although some do). In fact cement can cause problems if used with clay.

Last weekend I did a rammed earth course run by the Brighton Permaculture Trust, hosted at the Brighton Earthship. Earthships are passive solar, off grid buildings. The Brighton Earthship was completed around 2006, and it showcases various natural and alternative building methods. It’s a wonderful thing. Not everything that’s been tried has worked out, and I think they are planning to make some improvements, but that is part of the joy of learning and experimentation that can also be shared with others. I rather foolishly forgot to take any photos of the outside, but there are plenty here.

The course tutor, Rowland Keable, has amassed a tremendous knowledge of rammed earth and he and his company – Rammed Earth Consulting – have done a lot of work to get rammed earth building standards drawn up and adopted – especially in Africa. The forecast was for a sunny Saturday and wet Sunday, so we did most of our building work on the Saturday, completing it in the rain on Sunday morning.

So, what earth can you use? The ‘ideal’ mix needs to be roughly 10% clay : 40% silt/sand : 50% graded gravel, but you can play with that a bit. This gives a mix of material that goes from say 20mm diameter right down to tiny clay particles, and as these all get rammed they lock together giving a tremendous density. Materials like chalk work too as long as you have this mix of sizes – this is what we used. To the mix you add just enough water so that you can make a ball of material in your hand that breaks into a few pieces when you drop it. If it completely shatters it’s too dry and if it stays in one lump it’s too wet. It really takes surprisingly little water. You layer about 100mm of the mix at a time into the formwork and then ram it down in to place. The formwork, as in the pictures below, can simply be timber boards – or much more expensive formwork used for commercial concrete work.

It really is an exciting way to build. Although you don’t have all the freedom of cob, for example, because you use formwork, you have the advantage that you can keep going up, by moving the shuttering up, without waiting for what you’ve built to dry. It appeals to my sense of order and it’s really very straightforward to do. I love the way a straw bale wall becomes solid when it gets locked down into place and rammed earth provides similar, if not more excitement, as you remove the formwork. It’s somehow hard to believe it’s going to work – but there it is – a solid wall made of stuff dug out of the ground! You get a lovely clean finish from the formwork too. Walls take a good while to properly dry out, but unlike other methods they can dry out as quickly or as slowly as conditions permit. Our example just needs a tarp on top, short-term, maybe some coping stones in future and it’s good for the UK climate. Yes, there are some more complexities to consider for each job, but it’s a great method to consider.

After unveiling our masterpiece, the rest of our wet Sunday was spent indoors with Rowland patiently answering our many, many questions about rammed earth construction. Rowland is a an inspiring speaker on this subject and clearly passionate about vastly reducing, if not totally eliminating, cement use from low-rise buildings. An excellent idea, seeing as cement is hugely environmentally damaging and structurally completely avoidable in such buildings. However, the barriers to this are many. I am sure I will delve into the world of building industry and government monopolies in a future post, but for the meantime it’s lovely to meet people like Rowland who not only acknowledge and are keen to point out that such things exist, but who are actually, bit by bit, getting things changed.

I heartily recommend this course (in fact the Brighton Permaculture Trust do a wealth of interesting looking courses) and giving rammed earth a go. I will talk more about specific uses of rammed earth in future posts.