PLEASE HELP. I am ready to pour my foundation this weekend. I have 3 pieces on calcium silicate insulation but it measure at about 1 5/8". Other than that issue, it is definitely the good stuff, I bought it at Western Industrial Ceramics. So here is question....Is one layer enough? or should I my more so that I can double on to 3.25-3.5" of calcium silicate. Please help.