I came across this very good explanation of how to add a bit more silicone to your silnylon tent/tarp to protect against heavy driven rain, which causes inner misting. I was not completely sure that this actually happens, until my last trip, where it clearly happened. All doubt was removed in my case because I had pitched the tent on a dry spot, relatively, thunder was booming in the distance, then it started to rain, then almost immediately, a heavy hail (3/8 inch or so), I got in my tent, zero time for condensation to form, and the misting started instantly, it’s very clear and defined, nothing to do with condensation, so if you read people trying to pretend this phenomena is just inner condensation getting knocked off by the outer rain, they don’t know what they are talking about, but probably think they do.
In an unrelated heavy rain in Norway discussion thread Eric Blumensaadt gave this excellent short summary on how to treat your silnylon to fix the misting problem, I’ve read several, and this one seems to be about perfect, thanks.
Re-coat the silnylon tent with a 5:1 ratio by volume of 5 parts of odorless mineral spirits to 1 part clear GE Silicone II (or European equivalent). Place in a suitably sized jar with a tight lid. Shake well to mix and shake every 5 minutes while using.
Apply in sections with a very short nap, narrow paint roller – pour small amounts in a roller pan. You can also use a fine bristle brush. Spreading the tent sections on a smooth top table is far better than using the floor.
BE SURE to wipe the excess off each section immediately with a heavy duty paper towel (“shop towel”). Rolling on the mix is faster and gives a more even coat than brushing. Wiping immediately after leaves only the necessary amount on the silnylon, thus reducing weight AND GREATLY REDUCES DRYING TIME by days. Silnylon floors or ground cloths (“footprints”) can be coated twice using this method for a heavier coating.
BTW, this procedure will seal the tent exterior seams but I would recommend also coating the interior seams as well. If seams ever leak after this treatment (doubtful) use a 3:1 ratio of mineral spirits to clear silicone caulk for re-sealing. Do NOT wipe this seam seal treatment. Just let it dry in the hot sun. The Netherlands does have hot days, right? My experience with Dutch weather was in late October when it was cold and rainy.
I didn’t want this little gem to just vanish in the never ending churn of gear talk etc on Backpackinglight.com, so I am saving it here so it doesn’t get lost.
Technically, I believe you can use Coleman white gas type fuel instead of the mineral spirits, and I believe silicone cures better in humid climate, though I’m not positive about that. Also of course, it’s hard to use rollers if you don’t have a big work space.