[Cob] Radiant Heat Flooring

[Shannon C. Dealy]

On Wed, 22 Mar 2006, Mark Gailmor wrote:

> I'm in the process of designing, for myself, a hybrid cob/straw bale home
> because I really want to take advantage of radiant heat. To my knowledge
> radiant heat isn't possible in a standard cob home because the heat may
> eventually crack the flooring. Does anyone know if there is any validity to
> this? I'd love to hear from someone that has successfully installed a
> radiant heat system throughout their cob home.

I haven't heard of any problems with the heat cracking the floor. 
Normally these floors are finished with linseed oil, which if properly 
done should bind it together pretty thoroughly and prevent any problems.
Some people use a very high clay content in their floor finishes and very 
little linseed oil which I would guess will make their floors far more 
susceptible to problems with cracking since the high clay will greatly 
reduce absorbtion of the linseed oil and as a result, the amount of 
linseed oil binding the floor surface.

To reduce the risk of cracking problems, I would recommend that you make 
sure there is plenty of straw in the floor mixes, avoid high clay finish 
coats, and fire up the system before the final finish cob layer is 
applied (preferably while the base layer encasing the heating system is 
drying) to allow any expansion and contraction to occur while things can 
still shift around a bit (it will also help it dry a bit faster).  I 
recommend you do NOT heat the floor for the finish coat(s) as the quick 
uneven drying will tend to make it crack.  For the linseed oil coats, 
quick drying with heat is also not a good idea as the surface will tend to 
dry out first creating a seal and trapping the solvents below the surface, 
giving the appearance that the linseed oil has dried when it hasn't.  Once 
the heat is removed and the floor cools, the trapped solvents will soften 
and disolve the surface layer sealing them in, so the floor will recover 
from this, but the overall drying time could actually be longer.

Yes, I did learn this the hard way.   This floor is relatively new so it 
hasn't had the test of time, however, I have had the surface temperature 
of it up to over 120 deg. F without any cracking.

FWIW.

Shannon C. Dealy      |               DeaTech Research Inc.
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