Loving this thread! Lots of great info, and I'm definitely going to try this soon. I decided to make a tarp for the upcoming backpacking season, and this looks like the way to go. I have a few (of course, untested) suggestions to possibly make the whole experience easier.
when mixing the solution you can make an easy stirring stick. just use a dowel or stick of some sort that you can chuck in a drill, and attach a few zip ties to the end so that the ends of them poke out in all directions. this makes an excellent, flexible stirring attachment for your drill that costs next to nothing. Score one more for zip-ties!!
For those of you who soak the material in the silicone solution I would suggest that you transfer the solution into a gallon ziploc bag, then add the material, seal, and you can do all the soaking, kneading, squishing, and squeezing that seems to be done here with the immersion method, but with less mess.
I just thought that I should share these ideas so they can be used before I get around to making my own tarp, because who knows when that will be...
This is a great thread but no one has given us a long term review yet. It would be great to read some field reports from the folks who have treated and used their tarps over the past several years.
Knotty what is that elbow piece on the stand in your pic?
I just tried this trick out last night with decent success for a first crack. I went 3:1 by volume on the mix, soaked for about 2 hours with lots of agitation and shaking (just did a little 8" square in a mason jar), only one treatment. It is waterproof under the faucet except for one or two small pinholes. If I force the water through under pressure, I get a more noticeable flow. I'm nearly certain both of those flaws are caused by the air bubbles that get in to the solution while mixing. I'm going to rig up a vacuum vessel and pull it down to ~1/4 atmospheric pressure and see if I can draw the bubbles out and get a more repeatable result. I'm also going to experiment with a slightly thinner mix, as that wouldn't hold on to the bubbles quite so stubbornly.
Using a vacuum could also potentially make it possible to treat fabrics that are more prone to holding on to air than ripstop. I'm also going to come up with a PVC roller arrangement to squeeze off the excess.
Anybody have any favorite sources for dirt cheap 1.1oz nylon? I'm having trouble finding it locally under $7/yard and on the internet, the best price I've found is about $4/yard on eBay.
The olive green fabric is really nice and a steal at that price.