Hi, great information in here. I have only just joined and wish I had have found it a few months ago. I have been mucking around with making a tarp from Ripstop and waterproofed it with a 1:5 ratio plumbers silicon:mineral spirits. The tarp is 10 * 10 and I soaked it, post sewing, in a tub with a lid for about 4 hours giving it a squeeze every so often. I hung it up for about a week and despite a few runs it come out really well and it didn't leak even when I had the hose on it, full force from 12 inches away. Even the webbing which I sewed down the ridge line didn't leak or become wetted. This tarp was a prototype for a big one I want to make: 20*20. In terms of mixing the solution I just added the spirits very slowly and mixed by hand: like making mayonnaise. No worries at all, took 10 minutes to mix up a litre or so. Weight isn't too much of an issue so I was pretty heavy handed and used a standard tube of silicon, but a lot remained on the inside of the container. I got my ripstop at a bargain price...errr...I'm converting it from metric....about $1.80 US per yard, 60 inch wide. So yeah a great cheap and pretty light weight tarp. Next: the big one.