<img class=" titleimg" alt="pu glue oozing" src="/images/audio/oddsAndEnds/glue-pu-oozing.jpg"/>
Over the past year or so I've pretty much switched from PVA to Polyurethane glue for most tasks. I've discussed this glue with other wood workers and in my favourite hardwood store SL Hardwoods of Croydon and all seem to agree it is a strong glue.
To me it has one very large advantage for audio equipment over PVA; which is that it expands to fill any gaps. So if the two pieces of wood being stuck together have any imperfections that could allow air through the glue will seal it. See the picture below for how the glue expands enough to ooze out of the sides of a joint. However, unlike normal wood glues, it does not stain and can be sanded out. As this glue expands while curing, it is important that the work is well clamped or held under tension while setting. See the example image or the you tube video linked below.
What is of interest is that the expanding foam equivalent, to which I think it is closely related, is used in soundproofing to expand into any gaps and create a seal. This same behaviour is very beneficial in speaker building.
In terms of cost, yes it's more expensive than PVA, but it's still only £10 for a reasonably large container, given no silicone seal is needed I'll gladly pay it. I've not totally given up on PVA, but every time I use it recently, I feel it's not got as good a hold as the polyurethane glue.
Here's a video by one of the glue manufacturers showing it in use: https://youtu.be/ddF5ZnBxyDY
Above: example where the glue expands so much as to exit the joint. As discussed above this is not important as it does not stain if left uncompressed, so can easily be cleaned. Just use a scraper after it has fully set.