I know I'm not alone in experiencing some misting under my tarp in a downpour. It's not really leaking; it's just very small droplets falling and tickling my nose just enough to prevent a deep sleep.
My main tarp is a DIY 10x11 with olive sil from OWF. I made it two or three years ago. It gets something like 100 days of use a year, and often gets stuffed into the pack soaking wet. I've noticed that this spring the misting was significantly worse, probably due to wear and tear on the fabric and the occasional sunshine beating down on the tarp (UV and silicone don't like each other). A few weeks ago, I decided to give the make-your-own-sil thing a try. I mixed up caulk and mineral spirits, taped the tarp to the driveway, and went to town with a squeegee. I really tried to keep the application thin, especially since I was trying to reseal old sil, not create sil from regular ripstop.
I started camping Thursday night last week and it's rained on me all five nights since. The first four nights, I had the newly applied silicone facing up, toward the clouds. I was pretty disappointed to still notice misting. Last night, I tried flipping the tarp over, so the newly-coated side faced the hammock. Not a droplet on my face! I think I know why. I don't believe a misting tarp is actually leaking straight through. When I had the newly-sealed side facing up, the fabric underneath was still being wetted out by water vapor circulating under the tarp. Shine your light into the air under your tarp on a rainy night and you'll see what I mean; there is a lot of water suspended in the air. I think the degraded sil will soak up some of that moisture, which will then be propelled toward the hammocker by the percussive force of raindrops on the other side of the tarp. When I placed the sealed side down, the fabric closest to me couldn't hold much moisture anymore and the misting stopped.
Geez, that's a long-winded analysis, but if anyone else is being dogged by Chinese water torture, they may want to give it a try.
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