Wednesday, 22 October 2014

External lime render (enduit chaux exterieur)

Although possibly a little late in the season, I have decided to start rendering the external torchis as it will need protecting for the winter, especially the South wall which seems to be particularly affected by heavy rain in the winter months.  Due to a lack of time to experiment, I have decided on a recipe based on the Eyrolles book 'Torchis' as well as on a conversation with an artisan who studied at the Avignon school of rendering.  Ideally I would have done extensive patch tests with different mixes.  The artisan advised me not to include fibres in the mix (contrary to the book) and to use dried and finely filtered clay earth to substitute for a third of the 0/2 sand (in this case sable de Bayeux).   I have decided to use more lime than normal due to the lateness in the year.
The idea is to use a mixture of lime - Chaux CL (chaux aerienne) on its own would take too long to dry and would wash off in the rain ... however it is the most supple and breathable of the limes hence good to put on to an earth wall.  The chaux NHL2 is the most supple and breathable of the NHL limes but hardens on contact with water so it will allow the mix to dry more quickly and give a more resistant surface ...
So the recipe:
Lime paint (badigeon) applied to torchis: 50% volume NHL3,5 and 50% water
Lime render:  One volume of sand/earth to two volumes of lime
The lime mix: 50% NHL2 and 50% chaux aerienne (CL)
The earth sand mix:   2/3 Sable de Bayeux 1/3 dried and finely sieved clay earth
The process:
The clay earth is dried out on old windows
Kevin filters the dried clay earth in a 1mm sieve. 
This is mixed with the sand and then left to soak for 24

I scrape off any loose earth and
high areas

I paint on a mixture of 50% volume
 of chaux NHL 3,5 (lime NHL) and 50%
water which provides the 'glue' between
the torchis and the render.

The limes were mixed in the concrete
mixer and the soaked sand and earth
added to this.  I then applied this mixture
directly to the lime painted torchis wall. 
It is always a good idea to protect the wall
with a plastic sheet (against the sun, rain
and cold)


No comments:

Post a Comment