of the layer if at extreme conditions condensation occurs on the coating the moisture is distributed in the surface layer without dropping occurring and the moisture evaporates later when conditions of higher temperature and or lower atmospheric humidity exist the granules perlite used in this example have the following approximate chemical composition ______________________________________silica sio sub 2 71 75 percent by weightalumina al sub 2 o sub 3 12 5 18 percent by weightpotassium oxide k sub 2 o 4 5 percent by weightsodium oxide na sub 2 o 2 9 4 percent by weightcalcium oxide cao 0 5 2 percent by weightiron oxide fe sub 2 o sub 3 0 5 1 5 percent by weightmagnesia mgo 0 1 0 5 percent by weighttotal chlorides maximum 0 2 percent by weight______________________________________ the particle size of the granules lies within the range of 0 01 1 5 mm preferred weight ranges and preferred weight fraction for the constituents of the instant example are given in the table below also shown in percentages by weight unless otherwise indicated ______________________________________ preferably range about______________________________________vinyl acrylic copolymer 15 40 30wetting agent 0 05 0 5 0 1emulsifier 0 05 0 5 0 1titanium dioxide 3 15 5anti foam agent 0 1 1 0 5talcum 3 15 6 0ethylene glycol 1 5 3 0water 20 40 34soya lecithin 0 5 2 1granulate perlite 5 15 10cellulose fibers 1 5 2______________________________________ it can be seen from a comparison of the above example with the parent case that there is a significant reduction of contents of copolymer namely from 40 percent to 30 percent by weight which constitutes an important economic advantage in addition to the fact that the physical strength of the dried product is.