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COATING 5 - The SIL/SIL coating is leaking - how to restore

This problem can occur with old, well-used outer tent skins made from sil/sil nylon fabric (fabric finished both sides with silicone elastomer). The DIY cure described here doesn't give you the same finish and durability as the original factory-applied coating but, when the alternative is retiring and discarding the whole tent it is well worth trying.

The process is one of painting an emulsion or slurry of uncured silicone rubber over the outside surface of the entire outer tent. With reasonable painting skills, working quickly with a wide brush to achieve a thin, even film thickness, you can get a good result (see the picture below). If you are not confident in your brush skills ask a friend who is. The new coating will have a slightly tacky feel for some time. It is important to wait for a run of fine, warm weather before proceeding.

A closely related DIY page is SEAMS 4: Restoring seam water-repellency using silicone emulsion. If the leakage problem is not with the fabric generally but just along the seams - go to that page now.

The ingredients and tools required are a tube of CLEAR Silastic® RTV or other high-quality silicone sealant - roof and gutter sealant is fine, a litre of mineral turpentine and a 75 or 100mm wide paint brush - all quite cheap and obtainable from just about any hardware store. Don't choose the cheapest brush. It will loose bristles while you work, leading to unnecessary frustration.

Clean the outer tent thoroughly to remove any dirt or dust. Use warm water, detergent and a soft sponge - then hose off thoroughly. Do this with the tent up in the direct sun, pitched tautly. After ensuring all traces of detergent are washed off let it dry out completely - nylon fabrics take longer than you might expect. Once dry a gentle wipe over with a rag dampened with mineral turpentine is probably an advantage in assisting adhesion of the new coating. Re-pitch it in the shade, this time as tautly as you possibly can. Do not do the coating work in direct sunlight. Unless you are a highly skilled painter the mixture will stiffen before you can brush it out evenly.

Mix one part silicone sealant with three parts turps in big glass jar. 300ml of mixture will cover a typical two or three-person tent easily. Fasten the lid and shake vigorously until the silicone fully emulsifies with the turps. With a large quantity this can take some time until all the globs of sealant are emulsified. The final consistency should be like that of a thick plastic paint, easily brushable but not 'runny'. Shake in a little more turps if it looks too thick. For the application stage transfer the mix to a wide mouth container suited to the wide brush. A 2 litre plastic ice-cream container works well.

Apply the silicone slurry with the brush, spreading it out to a thin, even film as quickly as possible. Do not allow puddles or runs to set! Spread them out. Avoid unnecessary lapping back over areas already covered. Work the coating well into the seams. It is impossible to avoid some streaking but that's ok. The turps will evaporate quickly and the silicone will then also set quickly as the acetic acid leaves the compound. Unfortunately, when you are finished, you will probably have to discard the brush because, to clean it thoroughly requires far too much turps.

Leave the tent for a few days so the silicone can fully cure. Do not allow the fabric to touch itself during this time and avoid dew falling onto it (just to be on the safe side). When the tent is ready to pack away the coating should not be sticky. Test this by pressing the coated surface against itself for about 30 seconds. It should separate immediately the pressure is released. Although we have not found it necessary to do this any residual tackiness can be eliminated by dusting the surface with talcum powder. The disadvantage is that this leaves the fabric with an somewhat unsightly appearance. Test a small area first and decide for yourself.

The seam sealing version of the above process is identical except that you use a narrow paint brush working only along the seams AND immediately wipe off the excess silicone with a cotton rag so sealant only remains in the stitching and under the seam's fabric overlaps. You should paint no more than one metre of seam length at a time. Longer than this will not allow you to properly remove the excess slurry and the finished job will not be nearly so pleasing in appearance.

This old tent has been treated as described above. The water is beading on the surface and both the fabric and the seams are now effectively waterproof.

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