Tuesday, 29 July 2014

Terre paille banché - isolation (straw and slip insulation)

So now about three quarters of the way through insulating the torchis walls of the house with a mixture or straw and slip insulation.   Pros?  It's cheap (2 to 3 euros a bale of straw and the earth is free if you dig it up from your land).  If you have lots of friends/family/ and/or ability to organise chantier participatifs it can be lots of fun to do together.  Cons?  It takes a long time to prepareand  put in place and can take many months to dry before being able to render.

Anyway - straw and slip insulation in a  nutshell:


Above left: I use one bucket of clay soil to one of water mixed in the concrete mixer then poured out through a sieve into a container of straw (no pre-seiving required in this case as the earth here has no stones - just clay and silt)
Above right:  I use a curved pronged fork to mix the straw with the slip
Above left: Using the fork, the straw soaked in slip is lifted out of the bucket into a wheelbarrow

Above right: Tip the straw and slip mixture onto wooden pallets to allow the water to drain off for 24 hours.  It is a good idea to cover the mixture with a plastic sheet to prevent it drying out.
Above: OSB board or bits of plaster board (easy to cut) were used to create a 'coffrage' into which the mixture is tamped - use small wooden battons to compact the mixture.  We screwed through the boards into wooden uprights leaving a gap of a few centimetres between the boards and the uprights so that the mixture could cover them.  Use a builder's level to make sure the boards are vertical.
Above:  The first section of wall took me around three weeks to do on my own!! And it is not too even or vertical. I got better over the weeks


Above:  The third section of wall - much more even.

Above:  I find the best method to hold the mixture in place is to cut lengths of thin wooden batons to fit between the uprights (BricoMarché have loads of these lying around outside that they let you take for free), push them down to compress the mixture while it is still held by the OSB boarding and then drill screws through their ends diagonally into the uprights (see below).

I leave the boards on at least 12 hours then move them up for the next intake.

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