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SEAMS 1 - The factory-applied seam tape is lifting or peeling - heat-setting

There are a number of reasons why the tape used to factory seal the seams on the PU-coated side of a tent skin, rainshell or dry bag for example may fail.

The problem may show up as delamination of the tape, in places like folds or thicker seam intersections, or over a longer length. One reason for this may be exposure to extreme heat. In this case the 'hot-melt' adhesive layer of the tape has softened and built-in tension in the tape causes it to lift away in places. Few PU seam tapes can withstand temperatures above 50 or 60 degrees celcius and not lift.

Otherwise the tape problem may be a physical degradation due to a chemical contamination, possibly from unintended exposure in use - insect repellents are often a problem, sometimes from natural oils produced by human skin - most likely to be evident in rainshells. Sometimes excessive fabric coating additives, like flame retardants, might be responsible after slowly migrating into the tape layer.

Provided the fabric coating is in good condition there may be some hope of repairing the seam tape problem. If the old tape can be removed entirely it should be. This is done by heating it with a hot air blower set on the lowest effective temperature and peeling up the tape using a pair of long-nose pliers to hold an end. With the tape removed it is then possible to re-seal the seam. This must be done by a professional repair service with the necessary equipment. The whole job is quite time consuming and you should ask for a quote before going ahead - it may not be an economical fix.

A possible DIY solution is to try 'heat-setting' the seam tape using a domestic iron. In some cases this can be effective in re-adhering lifted or delaminated tape that is otherwise in good condition. A well-equipped repair service would use a hot press to do this, working section by section along the seam. At home a domestic iron set on its lowest 'one dot' silk setting and using a non-stick or paper layer between the iron and the inside of the seam where the seam tape is, can work. (The perfect non-stick material for this job is a Teflon®-coated fibreglass fabric. Look up for details).

First a test must be made on a small area of the item where some 'heat damage' can be accepted should the coating and tape prove unable to withstand the temperature and heat applied. The separating layer used between the iron and the fabric must also be proved. In some cases a simple layer of clean, unprinted paper will work. Photocopy paper is often suitable. On more heat-sensitive coatings a Teflon non-stick film like the one referred to above and shown in the illustration at right must be used. This is because the fabric coating or the seam tape may become sticky while it is hot. Briefly press the tip of the iron on the test area moving it back and forth a short distance one time only. If the fabric coating is unaffected and the small section of tape responds to the heat then try working over a bigger area. If either the tape of fabric coating stick to the paper do not proceed further.

The illustrations here show the results of heat-setting a badly degraded seam tape. The result is not in fact a waterproof seam because the degraded tape is not strong enough or thick enough to hold across the fabric edge. The waterproofing can be taken care of by following the instructions for applying a silicone treatment to the outside of the seam - see DIY page SEAMS 4. The effect of the heat setting here is to delay further flaking and disintegration of the seam tape, something worth spending half-an-hour on if it works.

The heat setting shown at right was done using the Teflon film, with the iron set on the one dot (lowest) position (about 150 degrees C) and with just an 'up and back' pass of the iron so as not to allow too much heat into the tape and fabric. The lowest iron setting is still much hotter than the release temperature of the seam tape, down around 60 degrees C. This is why it is absolutely necessary to use a separation layer and to work quickly. (In the first test the iron was left too long in one place and it affected the coating).


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