[Strawbale]Earth/Straw plaster acting as fire guard

Rene Dalmeijer rene.dalmeijer at hetnet...
Mon Oct 18 00:31:53 CEST 2004


At 07:36 AM 10/18/04, you wrote:
>I'm building a non-loadbearing strawbale house in the south of Hungary (the
>walls should go up this weekend - weather permitting) and am considering
>making up a cream consistency earth slip, and then mixing this with lots of
>loose straw and 2-3% lime (lime water).  Then I can use this to plaster the
>walls immeadiately as the bales go up.

How about applying the French dip method instead. This consists of making a 
clay rich slip placing it in a tub made with bales and lined with thick 
(black) agricultural plastic. What you are seeking is to get as much clay 
sticking to a quickly dipped straw in the soup you have created. Take a 
bale and dip its outside and inside surfaces in the slip. Voila Stack the 
bale in the wall after a while, about 2 hours, you can start tamping the 
outside wall surfaces with a short plank roughly 45x100x600. The tamping is 
done with a normal carpenter hammer, on the plank obviously. Start doing 
this at bale intersections and then work into the planes of the bales. What 
happens; if the bales are well slipped, is that the slip coat evens out to 
an almost smooth surface; at the same time you also even out the bale 
intersections. The resulting surface is perfect for the next second coat 
(which is straw rich)

>I'm hoping that if this initial plaster is a couple of centimetres thick it
>will provide fire resistance until I can plaster the walls with more
>attention.  (Which might be in spring)

The French dipped bales suffice already quite well. It also avoids a lot of 
loose straw whilst building, the main fire hazard.

>The earth on site seems ok - I have made some test samples and they stick
>to the bales ok - although I have to add a lot of sand (about 2/3) to stop
>them cracking.

Don't worry about cracking the first layers should crack otherwise there is 
not enough clay for sufficient adhesion. If it dosn't crack there is too 
little clay for the first layers. As you work outwards you use more straw 
and sand. The last layer should not crack off course.

>Has anyone had any experience with just earth/straw plaster - would you
>recommend it and if not what would you recommend instead?

Depends on the earth off course I have seen it done. It could work as a 
second layer if the clay content of the soil is not too high. I would 
prefer using some sand on your condition as you seem to have quite clay 
rich soil.

>Although the earth on my property seems ok -

How much silt do you have? did you check that?

>there is also a deposit of
>clay not too far from my house which is used by potters - is there any
>advantage of using a more pure clay - it will result in much more cracking
>won't it?
>Any ideas, I'd be grateful.


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