Did a 1m x 1m window bay test panel yesterday using a perlite mix. The mix is :a 6:2:2
10l perlite, 2.5l sand ( 1.5l sharp-5mm down and 1l soft/building sand)
2.5l N.H.L. 3.5 with synthetic hair /fibers in the gauging water.
1 cup of N.H.L.5 and 3 cups of silver (kiln dried .5mm down) sand.