What is self-amalgamating tape and how do I use it?

This is genuinely different from every other tape. There is no adhesive on it at all; the material bonds only to itself, and it does so under pressure. That makes it useless for sticking one thing to another and excellent for making a watertight, insulating, vibration-resistant sleeve around something cylindrical.

Safety

What you'll need

• self-amalgamating tape of the right width
• a clean dry surface
• scissors, though it tears by hand
• a cloth and isopropyl alcohol

Step by step

1. Check it is the right answer for the job.It is right for a garden hose, a low-pressure fitting, an outdoor cable joint, insulating and waterproofing an electrical termination as an outer layer, wrapping a handle, or holding a splint or a hose clip in place. It is not a repair for pressurised plumbing, heating or gas, and not a fix for damaged fixed wiring.
2. Clean and dry the surface.It bonds to itself rather than to the surface, but grit and oil under it stop it seating and let water track along underneath. A wipe with alcohol and a dry cloth is enough.
3. Remove the backing film as you go.Most tapes have a plastic liner on one side. Peel it away a little ahead of the wrap rather than stripping it all off first, or the tape will stick to itself in your hand.
4. Start one tape width beyond the damage.Anchor the first turn on sound material, wrap it fully round once with no stretch to locate it, then begin stretching.
5. Stretch it hard — to roughly twice its length.This is the whole technique. It should visibly narrow as you pull. Under-stretched tape does not fuse properly and will unwind. Stretched properly it fuses into a solid sleeve.
6. Overlap each turn by about half the width.Half-lapping gives two layers everywhere and guarantees the tape is in contact with itself over the whole surface. Butting the turns leaves a spiral seam.
7. Finish one width beyond the damage on the far side, and press the tail down.Release the tension on the last turn so the end lies flat, and press it firmly. A tail left under tension is the one place it can start to peel.
8. Leave it to fuse.It becomes touch-solid within minutes and fully fuses over a few hours. It cannot be repositioned once it has started, so plan the wrap before you begin.

Tips

• It is the correct answer for an outdoor low-voltage cable joint after the connector: it is waterproof, it is not affected by ultraviolet in most grades, and it removes cleanly by cutting rather than peeling.
• It is excellent for building up a worn handle, a slippery grip or a temporary bandage on a tool, because it grips itself and nothing else.
• It works in the cold far better than any adhesive tape, because it has no adhesive to lose tack.
• Removal is by cutting along the sleeve with a knife — carefully, away from what is underneath. It will not peel off in a strip.
• Buy a colour you can see. Black is standard and a bright colour is better on anything you may want to inspect later.

Common mistakes

• Wrapping it without stretching — The layers do not fuse. It behaves like a loose bandage and unwinds within days.
• Expecting it to stick to the pipe or cable — It has no adhesive. If the sleeve needs to seal against the surface, the tension and the length of overlap onto sound material are what do it.
• Using it on a pressurised water or heating pipe as a permanent repair — It is a temporary containment at best. A pressurised pipe needs a proper repair coupler or a plumber.
• Using it instead of a connector on damaged fixed wiring — It is an outer waterproofing layer, not an electrical connection. Damaged fixed wiring needs an electrician.

Questions people ask