How To Waterproof Silnylon Fabrics
This article describes the rapidly growing use of silnylon fabrics in the outdoor industry and offers advice on waterproof maintenance and repair.
As used in the outdoor industry: Silnylon--silicone impregnated ripstop nylon fabric
The past few years have seen an explosion in the use of outdoor gear made from silnylon, especially the very lightweight and strong fabrics. This waterproof and windproof fabric is now used for many tents, rain canopies, tarps, ground cloths, rain suits, ponchos, packs, pack rain covers, stuff sacks, and clothes. Even the rain canopies for our Speer Hammocks are made from this remarkable fabric. This modern wonder fabric has certainly proven its usefulness in the world of outdoor gear.
Silnylon is even more popular in the manufacture of lightweight parachutes and kites. Although often referred to as 'silicone coated' nylon, this is a misnomer since the silicone, which is applied after the fabric is manufactured, actually wets and soaks completely through the fabric, unlike the earlier generation urethane-coated fabrics where the treatment remains on only one side of the fabric. Silicone is replacing urethane for outdoor use because it protects both sides of the fabric, is lighter weight, and lasts longer.
This widespread use of silnylon brings up the issue of durability. How long will it be waterproof? Can it be maintained and/or repaired? How? The good news is that the silicone, which is primarily responsible for making the fabric waterproof and windproof, will last for many years. The application process thoroughly soaks the fibers of the individual threads themselves, thus ensuring that the silicone completely impregnates the fabric. Regular outdoor use, such as stuffing or storing in a carry sack, or deploying for rain/wind protection, do not cause deterioration of the silicone; in fact, the treated fabric remains soft and pliable even at sub-zero temperatures.
However, the silicone is slightly water-soluble and repeated long exposure to rain, or repeated washings, can render the fabric less than completely waterproof. Unlike urethane-coated fabrics, that are susceptible to non-repairable deterioration over time, silnylon fabrics can be easily and inexpensively re-treated when needed!
Consumer-applied silicone is highly effective in restoring full waterproofing in most fabrics. Silicone liquids and sprays for this purpose are readily available on the market today; they are inexpensive and can be applied easily and quickly. Once-a-year treatments are recommended for fabrics under normal outdoor use. Twice-a-year treatments may be needed for fabrics that receive lots of use. Fabrics exposed to rain only a few times a year, may not need re-treatment for many years. However, note that consumer-applied silicone may be less permanent than factory-applied silicone. Washing with detergent also removes a certain amount of silicone and multiple washings may significantly reduce the ability of the fabric to repel water.
Silicone aerosol (w/ 10% silicone) is probably the best option for most silnylon owners since it is readily available and easily applied. While several brands are available, Silicone Water-Guard® is a popular one found at many outdoor retailers, including Wal-Mart. Ever-Dri brand, which comes in aerosol or liquid, can be found at many military surplus and/or shoe stores. ScotchgardTM is perhaps the best-known silicone aerosol. A search engine such as Google will provide many Internet retail sources.
Silicone liquid (w/ 5-10% silicone) may be more appropriate for treating seams since it allows application with a small paintbrush or sponge. This concentrates the liquid on the area of concern and limits 'over splash'. A suitable brand is Aqua-Tite®; however it is only available in 1 quart or larger bottles, which is far more than most folks will ever need. I have found a useful small bottle of similar liquid silicone with a handy sponge-top applicator at some outdoor retailers, but the brand name is unknown. Ever-Dri, mentioned above, also comes in small bottles with a dapper applicator. Again, a search engine such as Google will provide many Internet retail sources.
Additional brands of silicone aerosols or liquids can usually be found in RV and/or Marine stores. Silicone liquids used in the Construction/Home Improvement industry may also function on fabrics; however, the ones I've tried leave the fabric brittle and much darker in color.
Be sure and follow directions when using silicone aerosol or liquid since the petroleum-based solvent carrying the silicone is hazardous to your health and plenty of ventilation is advised during application and drying. Quickly worsening headaches are often my first indication that more ventilation is needed!
Treatment consists of soaking the entire fabric or area of concern making sure to wet both sides of the fabric by applying silicone to both sides. If treating seams, be sure to completely soak the threads as well as the fabric that surrounds the seam. After the first application has dried to the touch, a second application is recommended to help ensure waterproof-ness. Two aerosol treatments to an 8' X 5' piece of 1.9 oz/yd2 ripstop nylon add about 0.6 oz to the total weight.
Note that silicone treatments do not completely 'seal' fabrics or seams in the same manner as urethane coatings. Instead, silicone simply causes water to bead up on the surface exposed to rain, allowing it to run off or evaporate instead of wetting the fibers and soaking through to the other side. Thus silnylon is 'waterproof' only up to a certain pressure; at higher pressures, water can be forced through the fabric. Fortunately even a heavy driven downpour does not generate enough pressure to cause well-treated silnylon to leak.
Seams in your silnylon fabric deserve special attention. They can be treated with silicone liquids or aerosols as described above, or with seam sealant glues. When silicone liquids or aerosols are properly applied, as described above, they are often sufficient to waterproof seams. However, greater peace of mind may come from using silicone-based seam sealant glues.
Avoid the non-silicone-based seam sealants, which are commonly used to treat seams in urethane-coated fabrics, since they will not adhere properly to silnylon. Only silicone-based sealants should be used on silnylon.
While slower to apply than liquids or aerosols, glues may last as much as twice as long before re-treatment is required. Sil-NetTM is a popular and readily available silicone-based seam sealant. It can be purchased in 1.5-ounce tubes at most outdoors retail stores or over the Internet--this should be enough to seal the seams in a small two-person tent. Be sure and follow directions on the tube and again provide plenty of ventilation. Lightly coating the dried seam with baby powder is recommended to prevent it from sticking to the rest of the fabric when stuffed into a carry sack.
The following homemade silicone glue directions are taken from the book Hammock Camping, The Complete Guide to Greater Comfort, Convenience and Freedom, by Ed Speer 2003 (see the book at: http://www.hammockcamping.com).
A simple and inexpensive seam sealant can easily be made from a 60/40 mixture of clear household silicone sealant or silicone caulking and a solvent such as gasoline. Any clear silicone sealant or silicone caulking from a hardware or home-improvement store works fine; it can generally be purchased in quantities as small as 4 ounces, which is enough to seal hundreds of tents. The solvent can be automobile gasoline or camp stove gasoline; however, extreme caution is necessary when using these highly flammable and toxic substances. The solvent dissolves the normally thick silicone sealant or caulking and makes it much easier to spread on the seam, after which the solvent evaporates and leaves the silicone in place. The solvent is not in contact with the nylon fabric long enough to harm it. About 1/4 ounce of this mixture is all it takes to seal both sides of an 8' seam, such as the one on the Speer 8 X 10 tarp (1/2"-wide, double stitched seam). Avoid breathing the solvent fumes by working in a well-ventilated area.
Mix the items in a small squeeze bottle using the head of a nail as a plunger/mixer. If necessary, enlarge the spout's exit hole with a straight pin heated in a small flame; hold the hot pin with pliers and keep the flame away from the gasoline! If a suitable squeeze bottle is not available, the items could be mixed on a paper plate and spread over the seam with a plastic picnic knife. Let the sealed seam dry 48 hours and then coat it with baby powder; otherwise it will continually stick to folds of the tarp when stowed away.
Sun rot is probably a more serious threat to silnylon than loss of waterproofing. You can replace waterproofing, but you cannot repair sun rot! You can reduce sun rot by limiting exposure to sunlight; bright, direct sunlight is particularly harmful. Try to set up in the shade and remember to put away your tent or tarp during the day.
With occasional re-treatment as needed, your silnylon fabrics can remain in service for many years; even 10 to 20 years are not unreasonable expectations. The good news is that with proper care you can enjoy years of service from this wonder fabric!
....Ed "Not To Worry" Speer Sep 29, 2003
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