The process is covered in a chapter titled "cement coated bags for poultry houses" in ""cement and concrete for the handyman" A "Domus" Book" 1951 Melbourne Australia. Pages 90-92.

It says to use 12oz hessian as the weave is loose enough for the cement to penetrate.

Also mentioned in the Werribee Shire Banner (newspaper) Thu 8 Feb 1945 attributing it to "the Victorian Journal of Agriculture".

Both say 1.5 gal water, 12 pound cement, 2 pounds lime, 1 pound common salt, 1/2 pound of alum.
Disolve alum in two pints of water seperatly, the salt to the remainder of water.

Mix cement with the salted water and when thouroughly mix add the alum water and mix through.
1 coat on the outside, one on the inside. Before they dry do another coat on the outside. Suggests adding further coats will make a stronger board.

Further says the second outside coat can be equal parts fine sand and cement, as long as final coat is the original mix, as this is waterproof.

Hope this helps

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