Dry and cozy in your sleeping bag, you hear the first raindrops hit the rain-fly. You drift back to sleep. You are awakened when the wind picks up, and the sides of your tent begin to shake like a flag blowing in the breeze. That’s when you notice the damp floor. You feel the windward side of the tent wall, and discover a small tear. Through the tear, a steady stream of water flows down the inside wall and accumulates on the floor. Unless the rain lets up soon, you know you are in for a night of mopping and wringing. When your tent dries out, you know you will have to make a repair.
To Repair or Not To Repair
Our discussion here is limited to patching a tent, rather than repairing seams, grommets, or frames. Any discussion of patching fabric has to begin with a discussion of the fabric itself because not all fabric is worth repairing. Tent fabric, whether nylon, canvas, or vinyl, is susceptible to a host of ills that weaken the fabric to the point where a repair will not hold. When you repair an area with a patch, the tension that caused the original tear is simply transferred to the fabric surrounding the patch. If the surrounding fabric then tears, you have wasted your time making the repair. Before you attempt to patch a tent, pull on the fabric surrounding the tear to make sure that it, too, does not tear.
Preparing the Surface
If you determine that your tent’s fabric is in good enough condition to hold a patch, the next step is to prepare the area to be patched. Both nylon and canvas are woven, and vinyl is sometimes fiber-reinforced; tears often leave ragged, frayed edges. Use scissors to cut away the frayed area; if necessary, cut into the undamaged fabric until all frayed edges are gone. You will be gluing the patch, so clean around the damaged area with denatured alcohol to clean off any fabric treatments and dirt. Clean both sides of the fabric. If the tent is vinyl, scratch the surface around the tear lightly with fine sandpaper to increase glue adhesion.
Making the Patch
The best fabric for a patch is the fabric that matches your tent: use a canvas patch for canvas, a nylon patch for nylon, and a vinyl patch for vinyl. Cut the patch twice as long as the length of the tear, and at least several inches wide on each side of the tear. Cut the patch in an oval shape, because square corners will tend to peel when the tent is flexed. It is important that the patch is sufficiently large. Patches that fail do so along the edge of the patch, because the cloth flexes more at a point where a great thickness (the patch) meets less thickness (the fabric). To prevent failure there, make sure that the edge of the patch is far enough from the damage that the load is sufficiently reduced.
Gluing the Patch
Glue is the best way to attach a patch, because when you use glue, the fabric won’t fray and the repair won’t leak. The best glue for patching is one which will adhere to the fabric reliably under all the custom iron on patches conditions (heat, cold, moisture, packing, etc.). Latex cement is often touted for tent repairs, but avoid it; it doesn’t adhere very well in extreme conditions. Contact cement performs well, but can be a little stiff. The glue recommended by tent rental companies is called Barge Rubber Cement, made by the Quabaug Corporation. It can be purchased at Ace Hardware and most hardware stores. Barge Rubber Cement stays flexible in just about any conditions you tent is likely to encounter, and over long periods of time.
Paint the glue on the back of the patch, and on the area surrounding the damage. Give the glue solvents a few seconds to flash off, and then press the patch onto the fabric. Be certain the edges of the patch are well glued. To be certain that the patch is well glued, support the fabric from underneath and hammer the patch with a rubber mallet or roll firmly with a rolling pin or veneer roller. For best results, patch the damage from both sides of the fabric.