I read practically every post in this thread and decided that I needed to go for it. I made a cat tarp last summer out of Joann Fabrics ripstop. I did this to save time and weight--I could not get sil here in the Valley. So, I used the 'ol Wally World orange can silicone spray. Works well...but. It will saturate, e.g. I was alpine camping this weekend at 8K ft, and it snowed on us 3" (on June 19!). I woke up soaked. I didn't want to resew a whole new tarp out of sil, so I tried this method. I've had PERFECT success using the following method:
2, 3" foam/sponge brushs
1 tube clear, GE silicone caulk
3.5 liters of Mineral Spirits (I used a 3rd of this, but I intend to use on other projects)
Clean 1 gallon can or coffee can (I used a plastic Folgers (YUCK) coffee can I got from a buddy and cut a whole in the lid to keep the slurry from spitting all over the place--worked well)
A) I used 3:1 by weight. I was not EXACT, but I did use a scale and got within a fraction of this ratio. Technically, I mixed two batches--one for each side separately as I needed them, so the slurry wouldn't set up on me. I used 39 fl oz. of mineral spirits to 13 oz of silicone. This left a bit left over at the end of each side, which I disposed of and started fresh. You don't want to run out half way through a side...do your best to keep a wet edge. I'd recommend applying when it's coooool outside.
B) Pitch your tarp as taught as you normally would. Mix your concoction thoroughly using your mixer. Pause and check that all of the silicone is "dissolved." It'll work into a milky color. If there are lots of bubbles, use a stir stick to minimize them with a slow stir. I'd let it rest for a minute or two. Don't wait too long, or your mix will begin to set up.
C) Use one of the sponge brushes and begin to apply to the first side. Apply to the non-glossy, flat-finish side. It is porous and will adhere well. The Joanne Fabrics ripstop has a shiny and flat side...You want to liberal, but do NOT slop it on. Find the harmony between too little and too much. If you're getting runs, you have too much; if you see dry fabric, you have too little. I ran a wet edge horizontally about two brush widths all the day down along the ridge line. I worked in every single dry spot I thought I saw. Anywhere I saw excess buildup, I smoothed out with the brush. Once I finished the first pass, I did a quick, dry back-brush over what I just painted. I did NOT double coat. I back-brushed... I used this process all the way until the first side was covered. I did not wipe off any excess.
D) Dispose of leftovers--lose those chunks, debris, and coagulated tidbits. You've done this much work; don't chince now!
E) Grab your new brush. By this time, the silicone has begun to set up in your first brush. Ditch it. It's worth the 70 cents to get the penetration you need.
F) Repeat step C above.
G) Depending on how humid it is where you live, give it a good 12-48 hours to cure. I live in sierra desert, so 12 hours was plenty.
H) Give it the mouth test first. Grab a section and try to suck air through it. Don't suck your brains through your nose though, 'cause it'll be tough!
I) Giver 'er the 'ol hose test. I don't buy the piddly "rain shower" setting from the hose. Blast away on jet stream from a close distance. Do you really want to wake up wet, alone, out in the bush? You get wet, you get cold; you get cold, you die.
J) Enjoy, brag, and celebrate your new, DIY silnylon!
SEE MY VIDEO TEST
: Clearly, if there was ANYthing coming through this, the lens would have misted up, be spattered, etc. you be the judge!
Cheers, guys. And thanks for all your discussion. I figured I'd do my part to contribute!