Wednesday, 10 September 2014

Earth renders on internal walls (enduits terres sur murs interieur)

The terre paille insulation(straw and slip insulation) and terre paille walls were now dry enough to apply earth renders.  After much reading and deliberation, I decided to treat the surface as you would a straw bale wall and to apply a slip (clay earth and water) as the first coat followed by a corps d'enduit of a mixture of cow manure, clay earth, hemp fibres (chenovotte) and sand 0/4. 
Normally you should do extensive testing of various combinations of all of these ingredients but due to time constraints I decided to go for an educated guess.  From tests that I had done last year I knew that the clay earth I have is around 20% clay and the rest silt.  Having this amount of silt in the earth is not great as the clay has to work hard to bind these particles which are not sticky - as well as the sand.  There are various things you can add to the mix to make it more sticky (wheat flour paste and cow manure for example) so in the spirit of low impact development, I decided on adding 30% cow manure (bouse de vache) which I had collected from a nearby farm.  I also knew that a mixture of one clay earth to one sand to one fibre produced a good render.  So I decided on a mix of one sand 0/4 to one clay earth to one hemp fibre and a third cow manure.
We soaked the cow manure and filtered earth in a bathtub for 24 hours and then mixed it in the concrete mixer with the sand, hemp fibres and water.  We then applied this by hand to the wall.  Some images of the process are shown below:

We applied slip by hand to the straw and slip walls

We used bamboo screening around the door
and window edges.  A thick gloopy mix of clay is spread underneath, the bamboo applied and slip applied over the top.

We fabricated 15cm long staples from old metal coat hangers then hammered them in to secure the bamboo strips
Preparing the earth render to go over the slip (corps d'enduit)

Kevin put the earth through a sieve

The sieved earth fills a third of the bath, 30 percent cow manure is added and water is added to three quarter full.  This is left to soak for 24 hours. 

I watered the wall before appying the render

John puts the ingredients in the concrete mixer - earth and cow manure followed
by the sand and finally the hemp fibres


Applying the render by hand

John uses a règle de macon to even out the renders

John uses a plastic taloche to smooth the surface after an hour or so

1 comment:

  1. A mixer is the best way to mix sand and cement rendering a wall. Screed battens fixed to wall to help level render. Use a straight edge to level up render.