Self-Amalgamating Tape Not Fusing: 3 Causes
The wrap came out loose, the layers separated and the tape gets the blame. In almost every case we are asked about, the tape was applied cold, laid too thin or wrapped over a contaminated surface. Three causes, three checks you can do at the bench.
Cause one: the tape was not stretched
Fusion is pressure driven. The surfaces have to be pressed into each other as each turn goes on, and that pressure comes from elongating the tape as you lay it. A wrap applied without stretch is a stack of ribbons. Check it by cutting the finished wrap: if you can see layers, it did not fuse.
Cause two: not enough overlap
A half lap, roughly 50 percent, puts every point of the substrate under at least two layers. Less overlap leaves single thickness bands, and those bands are where the wrap separates first. Check by unwrapping one turn and counting the layers over the substrate.
Cause three: the surface was contaminated
Fusion happens surface to surface, so anything at the interface stays inside the finished wrap. Oil, release agent, dust and moisture all become the separation plane. Check by wiping the substrate, letting it dry and looking at the cloth.
Symptom, cause and fix
| Symptom | Likely cause | Fix at the bench |
|---|---|---|
| Wrap looks banded, layers visible | Tape not stretched | Re-wrap with the tape elongated as each turn is laid |
| Wrap separates at the gaps | Overlap below half lap | Re-wrap with roughly 50 percent overlap |
| Ends lifted after a few weeks | First and last turns not anchored | Tuck the start and finish turns back over themselves |
| Fused everywhere except one band | Contamination at that point | Clean, dry and re-wrap that section |
| Wrap slipped on a smooth curved substrate | Low friction under a loose wrap | Stretch more and add a turn over the curved section |
| Wrap rotates by hand | Recovered grip is low over the whole joint | Re-wrap from a clean start with even tension |
The order that works
- Clean the substrate and let the solvent flash off completely.
- Peel back the release film as you go, not the whole roll at once.
- Anchor the first turn by tucking it back over itself.
- Elongate the tape as each turn is laid and keep roughly 50 percent overlap on the turn before.
- Press the finished wrap by hand, working along the joint.
- Tuck and press the final turn onto the layer below.
- Leave the wrap to settle before the assembly goes into service.
When it is not the technique
Silicone grades cover -60°C to +280°C, and a wrap that fuses correctly at the bench removes the tape from the list of causes. If the same roll fuses on one joint and not the next, compare the two substrates before you suspect the material. Silicone self-amalgamating tape is the grade we supply, and the wrap specification for each order carries the elongation and layer count for that job.
What to send
Send the substrate, the joint dimensions, the temperature at the hottest point and whether the joint is opened on a maintenance cycle. We return the material and the wrap specification for it.
Frequently asked questions
How much should I stretch the tape?
Enough that the surfaces press into each other as each turn is laid. The elongation for the grade you ordered sits in the wrap specification we issue with the roll, and wrapping cold is the usual reason a wrap never fuses.
Does the tape need heat to fuse?
No. Silicone self-amalgamating tape fuses at room temperature under contact pressure. Nothing cures chemically and nothing melts.
How much overlap do I need?
Roughly 50 percent, so each turn half laps the one before it and every point of the substrate ends up under at least two layers.
Can I wrap over a damp surface?
No. Moisture at the interface survives inside the finished wrap and becomes the plane it separates on. Dry the substrate and let the solvent flash off first.
The wrap looks fine but turns by hand. Why?
Even tension across the whole wrap rather than one slack band. Re-wrap the whole length from a clean start with the tension even on every turn.