April 17, 2011

Earth building #2 - framing and filling the walls

Here are some more details of the method used for the light earth walls.

Framing - The wall framing for the house is a double timber frame – two lots of 90mm x 90mm posts, with a gap of 70mm between, making a total thickness of 250mm. In places these are braced with a 70mm x 70mm diagonal to cater for our wind loading.There's no real need for light earth walls to be this thick, but we liked the idea of deep reveals around the windows and doors. Members of the Earth Building Association of Australia have used light earth infill in standard 70mm stud frame walls.

Filling the walls - One side of the frame is completely covered with ply, and the other with a series of narrow shutters (we used hardwood weatherboards), starting at the bottom and moving up as the earth mixture is placed in. As you move up the wall, the lower shutters can be removed. 
filling the earth walls

We found that a cut-down wheelie bin was ideal for moving the light earth mix into the house, and could be lifted up using a block and tackle.

Each layer must be tamped down around the edges to ensure the corners of the framework are filled, but the whole thing does not need heavy ramming – this would only squash the straw, which has a tube-like structure which provides insulation.
the last little bit!

The tops of the walls are tricky – not much room to manoeuvre here, so it was it was a case of shoveling it in by hand.

The process is slow, and as Christmas was approaching last year we were at 33% completion of the earth walls. We wanted some more progress before the family arrived for Christmas day, and decided to relent and hire some cheap manual labour from down the road. Toby (a real guy – not our cat of the same name) got into it. He increased it to almost 50% and allowed us to get the house almost weatherproof by Xmas. 

Unfortunately our excitement at the progress was short lived. Toby was a little too enthusiastic in tamping down the straw. A month after he left us to travel overseas his walls – like the walls of Jericho – came tumbling down! Closer inspection showed he had rammed so hard there was no strength left in the straw, and the walls, now little more than clay, did not hold together. So we’re now back to not much more than 30% finished.

Drying – depending on the weather, the walls took several months to dry out. Initially they would sprout shoots from the straw seeds, but once the earth began to dry, these would die off. As the walls dry, the clay shrinks, so the fill can subside a bit, and may need some topping up. The fully dried walls are hard, with no ‘give’. 

We managed to get some of our earlier, well-dried walls rendered before Christmas. We'll show the results in a later post.


  1. We are in the middle of an on-going projct which has lasted well over 20 years. Our house has a mudbrick bottom storey, with timber framed, and clad upper. We are now in the middle of tearing off the timber cladding and replacing it with light earth (we think it's a much better option in our bushy area in case of fire....once it's finished). We added extra timbers to the stud framing to thicken the walls, and basically replaced the walls with the mud and straw. It's been extremely satisfying, and we have also noticed a considerable improvement in the warmth inside the house in winter (Tasmania). Down side being living around the mess, but we're used to that, we've been in a building site for a long time now! What I'm really looking forward to is the plaster/render, getting the walls finished inside and out. We have so many ideas and plans, but probably not enough years now to realise them now :o( Happy building, I'll look forward to seeing your progress, ps I came across you in TOB

  2. Hi, good post this is very precise. Thanks for sharing.

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