Home / Advanced Backpacking Skills / How to Seam Seal a Tent or Tarp by Martin Rye

How to Seam Seal a Tent or Tarp by Martin Rye

Seam Sealing a Tent or Tarp
Seam Sealing a Tent or Tarp

When you buy a Tarp Tent, a silnylon tarp shelter, or a hammock tarp, it’s best to seal the seams using McNett’s Silnet (also called Gear Aid Silnet) in order to make them waterproof in the rain. Most of these shelters are not seam sealed or seam taped, so you have to do it yourself.

Here is my simple guide to do that.

You need:

  • A brush that you don’t mind throwing away afterwards
  • A tin can or something to mix up in
  • A bit of card, or a very steady hand
  • Damp cloth
  • Mcnett Silnet, which is sticky messy stuff
  • Paint thinner

Start with mixing at 3 to 1 paint thinner in a tin with Silnet until it is a workable viscous paste that can be easily applied with the brush to the seams. The whole point is to get it to soak into the stitching where the water could penetrate. If you were to apply the Silnet without thinning, it cures too thick and can flake off leaving a messy look.

Note: You want to seal the seams on the outside or top face of the fabric only. One coat is usually enough. Really.

Pitch the shelter in good weather or the garage: somewhere where it can dry for most of a day. Pitch the tent or shelter tightly, as you would in the field. If it has an unusual shape that makes it impossible to seal all of the seams at once, do them separately on a different day.
Brush in the thinned mix carefully and use the damp cloth to mop up any spills. A little goes a long way. A cut out template (shown above) will help reduce spills. The thinned mixture will soak in and look neat after it dries.

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18 comments

  1. Nice tip on the template. Thanks, Martin!

  2. Instead of Silnet you can use Permatex flowable silicone. You don’t need to thin and it can be used right out of the tube with the included nozzle.

  3. What is the advantages of this vs the spray on stuff you can pick up at Wal-Mart? I have used that on most of my tarps over the years and never had a problem, even in pretty intense rain.

  4. I just used standard clear silicone and paint thinner from Home Depot. You get enough to do all the tents in your town.

  5. Any advice on removing old, cracked silicone from an old seam seal?

  6. Is it just me, or is “3 to 1 paint thinner in a tin with Silnet” unclear to most anybody? So, is it 3 parts thinner to 1 part Silnet, or 3 parts Silnet to 1 part thinner? thanks for clarifying.

    • More thinner to Silnet. Dollop of Silnet and start with adding 3 parts thinner. Add more until you get a opaque liquid that is a good bit thicker than water. The aim is to push it into the seams and plug them stopping water ingress.

  7. I prefer to use a cheap sponge brush when applying seam sealer. They are cheaper and won’t leave little brush hairs that can compromise your seams.

    The template idea looks nice in theory, but having seam sealed more tents and tarps than I care to count I can tell you that it would not be very practical. First, it only would work on straight seams, so this would be useless for anything curved. Second, if your tent/tarp is from a cottage manufacturer, chances are that the seams are not perfect (this is true from some large mfg too), so using a template in this way would lead to missing sealing key seams. Third, moving even a 5 inch piece of cardboard over a tent seam with one hand and painting the seam sealer with the other hand leaves your can of sealant on the floor, or balanced on your head. There would be a lot of back and forth and a good chance you will loose track of where you are on a given seam. You want to get good overlap on your brush strokes and make sure you push the brush into the seams to get penetration. I agree that you don’t want a gloppy mess, but I have found the sponge brush helps control that if you brush with care.

    This article also leaves out a few key practices of seam sealing. First, let the sealer cure for 12-24 hrs. Then test it by spraying it with a hose on fine mist. Try to replicate a typical rain storm, change the angles and such, but don’t use the power nozzle. After spraying, check inside for any seam leaks or wetting through. These will be problem areas out on the trail. You want to take care of them now before you go out. Let the tent dry for 24hrs and reapply a coat of seam sealer to the trouble area and test again.
    Second, you need to pay special attention to stress areas of your tent or tarp where seams are stressed and can be more vulnerable to leaking. Look at beaks, door and window openings, corners and peaks, especially those under stress. Third, if your shelter has a floor, you don’t want to forget to seam seal the floor seams or the seams where wall and floor meet (we’ve all felt that ground splatter on the side walls from a hard rain). I’d also recommend brushing some wide Z patterns of thin seam sealer on your floor to help prevent your sleeping pad from sliding around; it is not a perfect remedy, but it helps.

    Most importantly, apply seam sealer carefully, but stingily; you don’t get better protection by applying more stuff, but you will get leaks if you fail to cover all seams properly.

    • Hi Neil,

      Having sealed many shelters I have never had more than a drip of water on a seam that harmlessly flowed along it dripping to the ground. That was after hours of hard rain. I never would, and could not be bothered to spray a shelter to test it after sealing it. I also doubt Tarp Tent or others would do that either. But they will charge to seam seal a shelter.

      On the card template. I state it will help reduce spills and it does. I and others have tried it with good results. You wont lose track of what you have and have not sealed, as one part will be dry and the part sealed will show as a damper area until left a few hours to dry.

      Also pitching it as you would in the hills, or wilderness will stress all the seams and you should then get the seam seal into those needed areas to make it a good water tight shelter.

      Nice informative comment and should help others get this simple task mastered.

      Thanks,

      • Hi Martin,

        Thanks for the reply.

        I am sure that your card method works well for you and others. Everyone finds a technique that works best for them and that new ideas should always be welcomes so I apologize if I came across otherwise.

        You mention TarpTent. Henry Shire over at TarpTent actually has a great video on seam sealing (http://www.tarptent.com/ttvideos.html#seamseal) for the DIYers. Henry is where I got the idea for using the foam brush and he suggested using a paper towel to rub in the silicone and I find it works well. I agree that my spray water testing suggestion is probably overkill and more for piece of mind for us neurotics and not a requirement. :)

        I agree with you that if done right, a single coat will do the trick.

        Cheers,

        Neil

      • Neil that foam brush looks a really good way to work in the sealant. Great link to TT and not noticed that one before. Thanks.

  8. Can you use paint thinner with Seam Grip too? I have a cuben fiber tent, and it seems that Silnet isn’t as good as seam grip for that material.

    • Drew, Unless you have an old CF shelter that’s been sewn, you shouldn’t need to seam seal it.

      As for Seam Gip, I’ve always been under the impression that it and Silnet are the same product, just with different ames.

  9. Seamgrip is polyurethane, Silnet is silicone. They are very different. You can’t use PU on sil-nylon, but can use sil on everything. Silicone is weaker than PU though and doesnt last as long in use. After using sil, you can no longer ever use PU.

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