Cob: Potassium silicate

[ortoneda]

Too bad that someone interested in cob does not know about this product. Potassium silicate is a natural product used by die-hard ecologists to paint their houses, there is nothing toxic in it, no outgassing and is the ideal paint for breathing walls, inside or outside. It works by petrifying the material it is painted on. Wonderful for cob (I would say indispensable) and the solution for sandstone. Sandstone block construction has been traditional in some areas of the Mediterranean for centuries, sad for houses: it calls for squarish, artless buildings, just the opposite of stone, but great for garden walls, for example. The problem with sandstone is that it absorbs water and turns grey and humid and the outside weather causes it to turn again to sand. Potassium silicate is now being used also by non-eco-builders on sandstone. I've seen it used beautifully also on limeplaster. One of the founders of GEA, the main eco-building association in Spain, and quite a purist, I might !
say, got the wrong kind of sand for the outside plaster of his house, having humidity problems. He mixed undilluted iron sulfate of the kind used in agriculture (even in organic agriculture) in the potassium silicate paint. Just after painting there was nothing to be seen but after a few days the iron oxidized, giving an amazing pictorial effect, and putting an end to his humidity problems. Potassium silicate was sold a few years ago only in laboratories, rather cheap. Then it came as a paint, then as a concentrate you had to dilute yourself, thus saving in delivery costs. The layest I've heard is that a firm in Germany has gone even a step further and they sell it dry in big sacks. I haven't tried it myself but I certainly will. Kill me if I know where to get it in Western Australia. I'll try to get the german address after the weekend and post it here, but out of Europe it would make little sense. Cheers
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    -   Mateu Ortoneda Colomar
                Infant Paga, 3,  1
               Palma de Mallorca
                    07010-SPAIN