what exactly is PU adhesive? what does PU stand for?
for now i've looked at bath silicone, No More Nails, Pritt stick, super glue, contact cement....

Sika flex polyurethane adhesive sealer

Doesn't have to be sika flex. I used polyurethane adhesive from car builder solutions and it is good stuff.

Or from a decorating supplier - same stuff but much cheaper......

Polyurethane sealant is black (usually), astonishingly sticky when fresh, and dries to a slightly rubbery but very tough finish. It's not acid like most silicone sealants, and much tougher.

Only down-side is that once a tube is opened then the life of the contents is limited to a few days, maybe a week or two. Then you end up with a tube of hard, slightly rubbery stuff!

Good stuff, I've used it in loads of places in my car.

Ive used the Wurth bond and seal version - probs the best i have found so far.

oh right.... i have heard of polyurethane foam for insulation. but thats not what i want.. ill look for the adhesive

thanks!

As an experiment I used exterior grade 'No Nails' from B&Q. Seems to be very similar and nothing has fallen off yet.

i used guttering sealant as sold in a diy store near you .cheap waterproof and black . as above nothing has fallen off yet. cheers scott