Sealing silnylon (enscapulated fabric) seams

by Jay Ham 2007-09-05
"Manufacturer’s instructions vary on this, but (trust me) a silnylon shelter does require seam sealing in order for it to be completely waterproof. If you have ever seam sealed a silnylon shelter, chances are you are familiar with McNett’s SilNet Silicone Seam Sealer. You might even have followed the directions on the package, as I have, and ended up with a very goopy, thick bead of SilNet along the shelter’s seams. It’s certainly waterproof, but it’s also unsightly and unnecessary to apply such a thick layer. There is a better way.

All that is needed is a thin layer of silicone to properly seal the seams, and a thin layer is nearly invisible when it dries. SilNet can be thinned with mineral spirits to improve its flow and ease application. Backpacking Light Associate Editor Will Rietveld showed me this technique, which he learned from Henry Shires at Tarptent, and it has worked wonderfully on several of my shelters. It also greatly increases the coverage you can get out of a single tube of SilNet. For example, a pyramid shelter generally requires two tubes of SilNet when applied according to the instructions. By thinning the SilNet, one can cover the eight seams with less than half a tube.

Your next question might be, “Won’t applying thinned SilNet reduce the seam’s water tightness?” I have not found that to be the case, and suggest the opposite is true. Thinned SilNet penetrates the stitching in the seams in addition to coating the surface. I have also seen conventionally applied SilNet tear along sections of seam that were not taut during application, a situation caused when the seam’s stress transfers from the stitching to the sealer. This does not occur with thinned SilNet. It should also be noted that applying thinned SilNet is much easier and less time consuming. The seam sealer takes from three to six hours to dry completely (depending on temperature and humidity). Give the shelter plenty of time to dry before packing it away, and you’re ready for your next trip."