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[Cob] double pane windows

Henry Raduazo raduazo at
Tue Aug 12 19:32:32 CDT 2008

Damon: Cob will shrink two ways. First it will shrink vertically and  
horizontally. Thus your opening will actually get smaller. To allow  
for this I put two inches of foam around a 2 foot by three foot  
panel. I had a mix rich in sand so there was only about 4 inches of  
shrinkage for the entire 10 foot wall height. You may have more or  
less shrinkage depending on the amount of sand and straw relative to  
	Second it shrinks from outside to inside. This is because the  
outside dries faster than the inside. So the wall will curl outwardly  
(just a little) and then straighten up. If you have an arch shaped  
piece of glass and you are building an arch around it you can build  
the arch so that only a tiny bit of cob overlaps the window on one  
side. Thus as the wall curves the tiny cob holding bits will give  
way. But, If you are doing a double insulated rectangular piece of  
glass and you are building an arch around this glass the upper edges  
of the rectangle are going to be deeply imbedded. This means that the  
padding must extend around the top and sides and at least one of the  
faces of the glass.
	I did not protect the faces of the glass and the outer pane broke. I  
now have a single pane window despite vast effort.
	I now have two options first: make a newspaper or cardboard template  
of the window, and using the template cut a second pane of glass,  
then fit the second pane of glass over the first pane of glass.
	It will not be sealed and it will have no desiccant between the  
panes so I may have to make it removable so I can clean it.
	The second option: I will just have a single pane window. I have not  
had a big condensation problem so the second option seems good for now.
	Regarding the word foam, that is any compressible material foam or  
rubber that can take an initial shape in supporting the cob off the  
glass and then crush or deform to let the wall move so your glass  
won't have to. The stuff on the top and bottom of your glass should  
not be too soft because it must support the initial weight of the mud  
but still crush when the wall shrinks.
	The foam on the front and/or back of the glass does not support any  
weight, but it should deform easily because it does not take much  
force on the front and back of your glass to cause a break.
I hope you have better luck than I had. Let us know if it works.
On Aug 12, 2008, at 1:20 PM, Damon Howell wrote:

> Ed,
> 	Thanks for the response. When you say "foam," do you mean  
> styrofoam? I have oodles of that stuff which I plan on using in the  
> roof. It came from a furniture store. I suppose if I cut a slit in  
> the foam then placed it around the edges of the glass, that would  
> cushion the pressure from the drying cob? It would also provide  
> insulation where there is usually a heat loss.
> Damon in GA
> On Aug 11, 2008, at 9:34 PM, Henry Raduazo wrote:
>> Damon: Are you going to imbed the double pane in mud as you build?  
>> I tried that, and I knew that the mud would shrink as it dried so  
>> I put a double layer of foam plastic around the edge of the pane.  
>> It broke anyway. I should have put a layer of foam on the front or  
>> back surface of the glass too and then cut out the foam after the  
>> mud dried.
>> 	It is tricky. Even single panes of glass will often break as the  
>> mud dries. If you look in the center portion of the sculpted house  
>> book you will see a window where we pre-broke the panes and  
>> provided mud mullions to look like the branch of a tree passing  
>> through the glass. There was one additional and unintended break  
>> despite the fact that we built so that only a 1/4 inch bead of cob  
>> was engaging the edge of the pane.
>> 	I would go for it, but pad the double glass well with a sheet of  
>> open cell foam on the front and close cell foam on the edges..
>> Ed
>> On Aug 11, 2008, at 3:26 PM, Damon Howell wrote:
>>> Hi folks,
>>> 	Could anyone tell me if it is safe to double pane my windows? I
>>> would like to, but if it's going to cause trouble in the long run,
>>> I'll just stick with single pane.
>>> Damon in GA
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