Replenishing silnylon – advice needed

no best, a number of equally good solutions, many threads about this in the past

100% silicone, for example GE.  Clear.  Don’t get the version that has mold inihibitor or dries quickly.

dilute with mineral spirits.  Don’t get the low VOC version or environmentally friendly version, it has stuff other than mineral spirits.

10:1 by weight, stir for several minutes until the silicone becomes uniformly mixed.

Foam brush is good.

If your silnylon has lost its waterproofness, has it also lost it’s strength from UV?  The color starts getting faded.  If you really pull on it it will rip.

Set your tent up so it’s really taut, apply, let dry for at least a day.  You could do it to a new tent which would increase it’s waterproofness.  Also give it some UV protection.

Here’s a post from Dave Chenault about recoating silnylon:

https://bedrockandparadox.com/2018/04/30/recoating-silnylon-shelters/

If I had to do a full tarp or shelter , I would use this :

http://www.atsko.com/silicone-water-guard-1-gallon/ using a foam paint brush for the application.

I did one shelter using a very highly diluted mix (something like 10:1) but it was still too much.