: Hi Brian,
: The glue foams as it comes out of the joint, not in it, except where there is
: a space. This removes any air pockets in the joints.

How do you figure that? The foam is air bubbles surrounded by glue.

: When I fibreglass, I
: get no air bubbles on joint lines (That could be also due to glassing in
: falling temperatures),

That's more likely the reason.

: It is strong,

Not when it foams. At that point, it's more like expanding foam insulating products.

: has a long open time

That's true, but it's also pretty slippery stuff, so the long open time give the parts more time to shift if they're not properly clamped.

: removes air pockets,

We've covered that.

: and if it foams is soft and easy to remove.

That shows you how weak the foamed glue is.

If you read the instructions on the bottle, they specifically tell you that you should use it with tight joints and firm clamping. The manufacturers know what they're talking about. I'm glad you've been successful using it, but it's in spite of it's limitations for strip building, not because of any special properties it has. OTOH, I use it for laminated paddles and other similar applications and it works great.