The polyurethane glue is really nice for some applications. I sheeted my wings with it and used it in numerous other places.

When doing my removable stab I was able to reduce the weight by using polyu rather than epoxy when gluing the wing tube in. Using the Bob Noll approach to doing a removable stab takes quite a bit of epoxy and polyu is lighter and expands quite nicely in the channel cut for the wing tube.

However keep in mind that when using the polyurethane glue you are supposed to "clamp" the items you're gluing together (normally just place some weight on it) or the glue will dislodge the item you're gluing when it expands.

I'm not sure about using it for a firewall, it may work fine but I'd be a bit concerned that the expansion could shift the firewall out of place. On the other hand, if you have it hanging from your engine and you place an equal amount all the way around it may be fine. Interesting idea for sure.

One more thing, don't over do it on the polyu glue. One of the guys I fly with put a ton when mounting his main wing tube and it started spreading the foam apart and seeping all the way from the wing tube to the surface of the foam. I have no idea how much he used, but it must have been a lot .

Keith