Switching from urethane to silicone waterproofing on tent fly

[Elliott Wolin]

I was going to order a lot of brush/spray-on urethane recoating liquid, but then saw some posts concerning switching to silicone.  I have a large nylon 6-p dome tent fly where the coating was failing, so I laundered it a couple of times and the urethane is gone.  Now I’m thinking it would be much cheaper to buy a bunch of silicone caulking, dilute it around 5:1 with odorless mineral spirits, erect the tent, put on the fly, and start rolling the mixture on.

Have people been successful converting from urethane to silicone?  Are there pitfalls to avoid, or a better procedure to follow?

[James Marco]

I have never done that and am following with interest!

[DAN-Y/FANCEE FEEST]

If you go the silicone route add some glacial acetic acid to the mix to insure a better adhesion.

[Edward John M]

DanY You might be mistaken there I think that neutral silicon is not compatible with vinegar

[James Marco]

Vinegar has water in it. don’t use it. Glacial stuff is the same but should  be around 99.5% pure acid. It is a byproduct of a normal silicone/h2o reaction. I am not sure that it does much for adhesion, but I would be willing to try it. I would *guess* it slows down the reaction giving the mix more time to flow and penetrate fabric fibers.Unfortunately, I don’t have access to my lab since I retired some 8-9 years ago and cannot test this.

Mineral spirits is *also* not compatible with silicone caulk. After mixing (one of the reasons for the long mixing time) it actually forms a colloid. The caulk actually requires a bit of water from the atmosphere to set. So, until this happens, it will not. White Gas also works but evaporates quicker…good in cooler weather.

I am unsure what would happen with a PU coating. IFF it has only one side coated, then it should work. I had an old tent that I coated that apparently had a PU coating on one side. IFF the caulk sticks, it will be fine. Try a small dab, let it set a couple days and try to peel it off.

As far as adhesion goes, if a film is less strong than the bond, it will stay pretty much intact. If the film is stronger than the bond, it will peel. One of the reasons for using thin layers (2-3 max) of caulk/mineral spirits is to help adhesion by forming a thin/weak coating. I have used 50:1 to touch-up my tarp several times over it’s lifetime. (The damage was usually caused by stretching around a pole or loop.)  It will also add a small measure of UV resistance to the nylon. (Note that it does not stick real well to poly fabrics, but thin coats work pretty well.) Before the thin coatings, several people would use thick 5:1 coatings and have those coatings peel off on silnylon and/or poly.

More on the 5:1 ratio, Elliott, I would dilute it to 10:1/15:1 and coat raw fabric(both sides) with it to make it waterproof. This is followed by a second coat of about 15:1-20:1 several days later on the outside. This was done to create a rain jacket after all the tape/seams/vinyl coating had been damaged (from about 20 years of use.) The vinyl did not seem to cause any problems on the outside, nylon layer, but the vinyl did not stick inside. The first time I used it, it flaked, rolled off, off leaving little flakes all over my shirt. This is peeling. It didn’t leak, though. I destroyed it(ripped and shredded) a couple years ago bushwhacking across some rather dense forest about 3 years later. Apparently it was heavily UV damaged, since I could just tear the fabric with my hands using a light pull. None of my tarps do this, soo, I assume it was UV.

[Jerry Adams]

Interesting ideas

I can smell a vinegar smell when silicone cures, that makes sense there’s acetic acid in it

Glacial acetic acid is like $10 on the internet

I had a bivy that had silnylon floor.  Coated it top and bottom with silnylon:mineral spirits.  It peeled off like James said.  Since then I’ve diluted it 10:1 like James has said and maybe it worked better.

I have a 40 year old tent that I never use.  I checked the urethane floor.  Still good.  I always carefully dried before storage – 1 week in unheated garage.

If the urethane is truly gone like Eliot suggests (except it would be easy to not notice that some is remaining) maybe coating with dilute silicone:mineral spirits would work.  Maybe it would work if there was quite a bit of urethane left.

What doesn’t work is putting urethane on silnylon. I don’t think that will work at all.

[James Marco]

Yeah, Jerry is correct. Nothing really sticks all that well to silicone except silicone.

 

[Edward John M]

Acid cure smells like vinegar, neutral cure smells like solvent. You need neutral cure to thin down. Any unused diluted mix will however start to set after 24 hours, so only mix up just enough to do the job. I do recoating all the time, my success rate is about 2 out of 3 using only one or several coats of very thin mix 1:5 usually but if the existing coat is still good as low as 1:10 works well

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