Rethink Your Life!
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The Work of Art and The Art of Work
Kiko Denzer on Art

[Cob] Weatherproofing a cob bench

yew yewberry at
Thu Dec 18 19:41:05 CST 2008

 >I have built a number of benches of cob.
 >We live in a semi arid area but when we get
 >rain it belts done. Not often but severe.
 >I have cobbed the benches and then lime
 >rendered them. Then I soak prickly pear leaves
 >(chopped) in water for three weeks and paint
 >this mixture on for waterproofing and the benches
 >are successful.

I'd do the same thing if I lived in the Desert Southwest, but I live in 
a climate that gets over 1000 mm of rain annually (over 2/3 of that 
falling during the winter months).  I wouldn't dare build a roofless cob 
structure here.  A lime render alone should be enough to protect a bench 
in your climate because the structure has ample time to dry out between 
rainstorms.  Occasional rainstorms, no matter how intense, aren't the 
same as month upon month of relentless wet.

I've done tests with various cob finishes (and cob mixes).  I've gotten 
pretty good results with a beeswax/citrus thinner mix, but it wears off 
before the end of the winter when left outside.  You'd have to renew 
such a coating at least annually.  I say just put a roof over it, and 
save yourself the hassle and expense of fancy coatings.