Gorilla and other PU glues

by Ken
(Kent, UK)

Hi, guys, I have discovered a couple of failings with the foaming type PU glues such as Gorilla and Lumberjack.

It seems that these glues are not very effective for gluing plywood which will take any kind of strain or be subject to changes in temperature, humidity or stress.

Happily I decided to test the PU glues on some unimportant work before committing it to boat repairs or building.

Experience of joints made about a year ago suggests that these glues get very brittle with age and start to break down with weathering - even though applied correctly and protected from the elements.

This was over a comparatively short period.

Delamination of the glue from the surface of the wood is also apparent, possibly due to the natural oil content of the hardwoods used in exterior and marine plywood.

Some of the glue joints where the adhesive has filled small gaps, show a crumbling of the hardened glue, and in others the glue has softened to a toffee like mess.

If you are considering using these adhesives on a boat, especially one which remains in the water, I recommend that you do some tests yourself first.

Myself, I will be only using good quality epoxy in future for any job which is of importance.

The quickness and convenience of the PU, does not for me outweigh the strength and reliability of either epoxy or indeed the best fully waterproof PVA adhesives.