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FABRIC DAMAGE 4 - Repairing tears and holes in PU-coated pack fabrics.

Polyurethane-coated and laminated fabrics are the mainstay of outdoor soft goods. PU provides a combination of waterproofness, light weight, durability and flexibility through a wide range of temperatures, all at an economical price. The coating also adds stability to lower density weaves where yarns would otherwise move or unravel at cut edges. Unlike the uncoated face side of the fabric, the smooth, PU-coated back side provides a good surface to which emergency repair tapes will usually adhere well.

There are a number of repair method options for small tears, punctures and nicks in PU-coated fabrics. Adhesive repair tapes can be used for temporary repairs, seam tapes with hot-melt adhesives for permanent repairs in lightweight fabrics and finally, liquid PU adhesive-sealant for all types of repairs in any weight PU-coated fabric and many un-coated ones.

Good preparation of the repair area is a must. Make sure the PU-coated surface you are going to do the repair on is clean, dust-free and dry. If you are in the field and carrying methylated spirits or a petrol-type fuel for a liquid fuel stove wipe the coating around the repair area with a rag dampened with fuel. If you have lifted tape and are now making a more permanent repair make sure you remove any adhesive gunk remaining from the old tape. Whatever repair method you choose, after cleaning and drying, hold the edges of the damaged fabric in good alignment by temporarily applying a tape on the un-coated side of the fabric. Painters masking tape or cloth-reinforced heavy-duty repair tape usually work well but anything temporary will do. You will remove this later. (Don't leave any temporary tapes in place longer than necessary. Aged tape can leave adhesive on the work piece that is not easily removed without using solvents).

Adhesive repair tape, applied to the coated face, will quickly restore waterproof-ness and prevent propagation of damage, particularly a risk in lightweight tent fabrics that are under tension in the field. The high-quality 'sticky-back' fabric used by sail makers for sail numbers and insignia is excellent for this purpose and can even work as the 'final solution'. Because it is formulated for high UV exposure and designed to be stuck to fabric the adhesive layer in this product is very durable. We carry patches of this material in our repair kit, obtained from our friendly, local sail maker. A lower quality option is the 'ripstop repair tape' commonly sold in rolls by your outdoor retailer. We prefer the effectiveness and versatility of the white cloth medical tape Leukoplast®, the one on the blue and white roll. Other repair tapes from your hardware store - cloth 'gaffer' tape, pvc duct tape and so on - are not generally suitable for long-term repairs as flat patches on flexible fabric.

Trim all corners on the patch to a rounded shape before you apply it. Carefully position and apply the patch to the PU coating, rubbing it down with a rag so the adhesive layer beds into the surface under it. Heat from the rubbing will also aid adhesion.

Seam sealing tape, used to factory seal seams on clothing and tents, is a neat option for repairing small nicks, tears and punctures in the lightweight fabrics used for tents an clothing. It is not generally suitable for heavier fabrics or where high strength, similar to that of the damaged fabric is required. Seam tape depends on a hot-melt adhesive layer for adhesion so its application requires a hot press device. The fact that it must be heated for application also means it is a more permanent solution that hand-applied tapes. With care a domestic iron can work well.

Please note, if you are attempting to repair the seam tape on a 3-layer rain wear fabric, one that has a nylon tricot mesh lining as its inner layer, using a domestic iron will not produce a waterproof result. Three-layer tapes need high heat and high pressure to force their thick hot-melt adhesive film through the fabric's tricot layer so a seal can be made with the mid-layer waterproof membrane. The shape of a domestic iron and the pressure that can be applied by hand  prevent an effective seal being made. You must go to a properly equipped, professional repair service for this job.

If you can obtain suitable seam tape for your simple coated fabric repair - some retail repair kit packages include them, sometimes the product distributor will help out - you then need to FIRST check that the heat needed to apply the tape will not further damage the fabric around the repair area. Start with the iron set at the 'one dot' silk position (about 150 deg C). You MUST use a separation layer between the iron and the fabric. A piece of regular 80gsm white (unprinted) photocopy paper can work well. The best option but difficult to obtain is the Teflon-coated fibreglass material used on hot presses. Look up for details.

Test a part of the item where damage to the coating can be risked. Press just the tip of the iron briefly on the paper, working it back and forth just once. If the coating is unaffected try ironing a larger area, ALWAYS with the separation layer. Keep the iron moving. If the fabric and coating are still unaffected and NONE of the coating transfers to the paper it may be safe to proceed with the seam tape repair. Follow the cleaning and edge alignment steps noted in the previous section. Now, with the PU-coated side of the repair upwards, place the seam tape face down on the coating making sure it is evenly overlapping the damaged edges (7mm minimum), cover it with the photocopy paper and use the tip of the iron to apply heat and pressure. Do not allow the iron into direct contact with the fabric. After about five seconds remove the iron and paper and check the tape adhesion by trying to roll back its edges. If necessary repeat the process with the iron on an increased temperature and working for a longer period. For seam tapes compatible with simple PU-coatings a temperature not above 100 degrees C is typically sufficient. Pressing on the tape with a cool cloth, while the tape is still hot, will help ensure even adhesion while the glue cools.

A liquid PU adhesive-sealant is an indispensable part of any outdoor repair kit and SeamGrip® is the go-to product in this category. Available at nearly all outdoor retailers we carry it on longer trips and keep a tube at home in the fridge. SeamGrip adheres to just about any textile or coating other than the 'rubbers'. These exceptions include silicone elastomer coated fabrics (see the separate page on repairing them), Hypalon® and latex. The preparation is the same as for the previous methods but now the masking tape on the other side is essential. SeamGrip can be applied over the tear directly from the tube. For long thin applications it is mush easier and neater to apply the liquid with a 10mm syringe. Squeeze the amount needed into the back end, fit the plunger, invert and expel the air. Because SeamGrip flows under its own weight the repair area must be flat and perfectly horizontal. Place weights, clamps or tape out the repair area on the flat, level surface. Allow overnight for the sealant to cure. It does this by absorbing water from the air. You can accelerate the process by wetting it. We use a wet finger to do this and you can also use this method to smooth the SeamGrip surface, as you can also with silicone sealant.

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