The completed fully water-proofed elastomeric protected earthen roof for the north room after seven coats of elastomeric/rubber/acrylic formulations. This approach was experimental, but when completed the result exceeded my expectations. This roof should be extremely durability and easily maintainable.
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The photo below shows a close-up of the elastomeric roof after three painted-on coats of AMES Research Maxi-Stretch. The surface looks a little rough, but that's due to the roof's clay/straw material make-up.
Close-up of drain receptacle with final coat of elastomeric (below).
The photo below show the earthen roof after three coats of Ames Research's BlueMAX Liquid Rubber. The coats of this liquid rubber followed the application of Ames Research Super-Primer.
The first challenge of building a rubberized membrane on top of a clay/straw roof was establishing an initial coat to attempt to adhere to a clay/straw substrate. This was accomplished with the use of Ames Research's 'Super Primer' which is a penetrating pure acrylic elastomeric plastic sealant.
Earthen (clay/straw) roof ready for the first coat of acrylic elastomeric sealant
The picture below shows the Super Primer acrylic as applied to the clay/straw roof.
A close-up of the dried Super Primer. You can see the straw that's fixed in the clay and also adhered to the Super Primer. Despite this whole process being experimental on my part; after this first primer coat, I had confidence the idea of building my own rubber/elastomeric roof from scratch would be a robust waterproofing solution.