Seam sealing question

[jaye_p]

OK, stupid question, but...on my diy tarps, should I seal the seams on the underside, top side, or both?

[WaffleBox]

Most people seal the inside.

[ZULUMASTER]

I've seen people post every option you listed and have not heard of a "best" way to do it. From what I've seen, the various reasons are as follows, I'm by no means an expert so hopefully those with more experience will chime in.

Top side prevents the threads from getting wet every time it rains and could help longevity. However it will leave a glossy looking finish to the outside and if your sealing isn't super neat, people will be able to tell (which you may or may not care about).

Underside is more aesthetically pleasing and hides the sealant but allows the threads to get wet.

Both sides will result in the best waterproofing but will also be heavier, the few people that I've heard of doing both either wanted the ultimate in waterproofing or chose to do one side or the other and found it leaked so they did the other side to fix it.

Personally, I chose to seal the underside of my tarp and it worked great in testing it with the garden hose. However, the choice will be what you personally value as most important.

[ZULUMASTER]

Also, for what its worth, RBTR instructions for their tarp kit say to seal the inside.

[Otter1]

I'm an outside guy.

I don't do both because it seems unnecessary and adds a tad of weight ( not a big deal if you do it correctly and don't GLOP the sealant on - dilute it properly and it's almost invisible and longer lasting since it won't peel off).

I don't do the inside because (and I've no evidence to back this up) water will find its way into the seam from the outside and will sit there...MAYBE working its way through eventually. Stupid, I know.

[T- Minus]

I sealed the inside of mine and on the outside just the line of stitching on the tie out material making sure none got on the outside of the tarp there is a shine to the sealant but hardly noticeable on such a small area. I figure since both materials are waterproof the only thing in question would be the material in the thread and the hole the needle made when it was sewn, so on the inside I sealed under the material where it was sewn and the stitching. I have had no issues and have been in out in the rain and storms 5 times testing it and am pleased with the result thus far. I used the flow-able sil from the auto parts store cost half as much as the sealant at the camping/sporting good stores and its the same thing go figure.

[jaye_p]

Thanks for the replies, everyone! I had sealed the inside, then thought, what if that's not how I'm supposed to do it... I love all the help I get here!

[rais'n hammock]

I seal the outside. It does not make sense to me to allow the water into the seam and then have it stop inside the seam or between the reinforcements. Water stuck in there will take longer to dry or worse never dry.

I asked this questions before and never got a clear answer. I even challenged the RSBTR instructions but still never got a clear response.

From what I have read it sounds like those who seal the inside do so because it looks better.

[justme2]

I'm an outie.

[powerboil]

Tarp from many brands are seal inside. Outside can be scratch by tree branch. Mostly seal by seam tape with pressure & heat, cover stitch line. But seam tape expire in 3-5 years. The best seal is seam grip, my tarp waterproof coat cracking but seam grip still good.