[Cob] Roofing material?

[Raduazo at aol.com]

I have been experimenting with paper/clay roofing  material built on a bamboo 
lath base. I consider this to be a temporary roofing  material because I do 
not know how long it will last. 
      I start with shredded paper and turn it  into pulp either with a 
drywall mud mixer on a 1/2 inch drill or with my feet in  a 1/2 of a 55 gallon 
plastic drum. I then add clay and sand. I have not yet  figured out the ratios, but 
it does not matter because you have to experiment  anyway unless you buy fire 
clay or ball clay in the bags.
    I then plaster it over the bamboo lath, and when it  is completely dry I 
paint with two coats of boiled linseed oil. I have an  experimental roof 
section and the real roof of a children's playhouse both 6  months old, and we have 
had plenty of rain here in the Washington, DC area. I  also have a Carol 
Cruse sculpture with a mica finish and one coat of boiled  linseed oil that has 
been out in the rain since the NBC-East. 
    One of my experimental roof panels is horse  manure and clay. Right now I 
am favoring the paper because you can build up  multiple layers to achieve 
the final surface. The wet paper/clay sticks to the  dry paper/clay with a layer 
of slip.
    I have some pictures around someplace that show the  layering process, 
and I am going to go back to the playhouse to take some more  pictures next week.
    I recommend a 45 degree slope on the roof, but the  test panel is set out 
nearly horizontal because I want to test it under the  worst possible 
conditions. We had three inches of snow and it melted over a  three day period with 
out doing harm to the panel.  I think that it is  important to have god 
ventilation under the roof because the under surface is in  no way water proofed, and 
thus it will absorb condensation if any is allowed to  form.
Ed