It is more likely that the water is slowly undercutting the bond. We do not typically recommend PURs for sealing under constant submersion for this reason. This should not be an issue with VHB, sealants, or flexible 2-part urethane adhesives.
Let me know if you have any questions
Thank you for your prompt answer. Today we use a PUR hot melt from Durant Italy. Just after gluing the result is excellent and it is harden very fast. Immediately after some months in sea water the glue is delaminating from the polyester weaving. We know that the PUR glue is ester-based. We also know from other applications that ester in water is hydrolysing. Can there be a possibility that this is happening here also?
The most extensive lab test we’ve done on this topic was a 10 year submersion test of 3M™ VHB™ Tapes. We used both fresh water and salt water in the test, and results are described in detail in this technical bulletin: http://multimedia.3m.com/mws/media/148318O/vhbtm-tape-underwater-durability-10-year-submersion.pdf
In this test, it’s important to note that the initial adhesion was good and performance was measured relative to that adhesion. So, when evaluating a 3M™ VHB™ Tape for this application, you should ensure that it meets your requirements on dry land first. You could also consider a thinner option such as 3M™ Adhesive Transfer Tape 9472. 9472 is a softer adhesive that will flow into the texture of the textile better than a thicker tape.
There are liquid adhesives you could also consider, but they will not for a bond instantly like a pressure sensitive adhesive like 3M™ VHB™ Tapes or 3M™ Adhesive Transfer Tapes.
Please post a comment if you have additional questions.