When nylon tents and tarps are new they usually do a good job of resisting rain. Usually, they have been treated in the factory with some sort of water repelling material. As time goes by, however, this material is broken down by UV rays and exposure to the air, so that the tent gradually loses its ability to withstand rainfall.
There are a number of products on the market that can be applied to the fabric to make it more waterproof. Kiwi brand Camp-Dry, Nikwax, CampKote, and AquaArmor are several of the products available for making nylon more moisture repellent. Most of these products are formulated specifically for making nylon fabric more water repellent and won’t damage your fabric. However, they are also fairly expensive and usually need to be ordered through the mail.
On an older or cheaper tent, it may be worth your while to try Thompson’s Water Seal. Water Seal is formulated specifically for wood and masonry and not for fabric- thus you run the risk of ruining you tent if something goes wrong. That being said, Water Seal is readily available, and not particularly expensive.
I tested Water Seal on a 40 year old nylon tarp that I had. It tended to bead quite a bit when I used a brush on the tarp, however, by rebrushing several times I was able to get it to coat the nylon evenly. Contrary to what I’ve read, it didn’t seem to damage the nylon (no shrinking, melting or pinpoint holes in the fabric that I could see). It took several days to dry completely and left the tarp noticeably stiffer than before treatment. Water sprayed on the tarp quickly formed beads and rolled off the sides. While I haven’t tested it on the trail, I would consider the experiment a success. However, I would caution against using this treatment on a new or expensive nylon tent.
Another consideration when waterproofing a tent is treating the seams. All tents, even new ones, need periodic seam treatment to keep water from flowing through the tiny holes that are left when sewing machines sew the seams together. As with waterproofing treatments, there are a number of products available, such as Seam Grip. All are based off of a silicone adhesive that is thinned to the point that it can soak into the seam threads and fill any small holes.
A homemade seam sealant can be made by mixing ½ part silicone adhesive (I use Shoe-Goo) with ½ part gasoline. Stir well until the mixture becomes a thin slurry (adding more gasoline to thin it if necessary). You will probably only need about ½ cup to cover all of the seams for a two-man tent. Using a small paint brush (like one that comes with a watercolor set), paint all of the seams of the tent. Be sure to do this outside in a well -ventilated area, and don’t forget to cover the seams on both the inside and the outside of the tent. The waterproofing will remain tacky for some time (usually several days) so be sure and let it dry well. If it remains tacky after that, a small amount of talc can be rubbed on the seam to reduce stickiness.
Hopefully, after the spring break pack trip, I’ll be able to test these waterproofing treatments and post results.
