I recently Hotwired an XPS block that glued together. I used gorilla glue, and when I hotwired the blank, it dug in at the glue lines leaving a void. This is my first time hotwiring so not sure if I did something wrong. What can I use to fix these voids in the foam? I was thinking of using spray foam. This board will be a compsand so I’m not worried about the appearance of the blank. The picture only shows one glue line, but there’s another near the tail. Thanks.
Q-cell/epoxy mix, XPS foam-dust/epoxy mix…
Glue seam looks thick. Glue-free 2-3" perimeter band between sheets of foam?
This is why I don’t like gluing up layers of foam this way. The scarf lines always make it hard to get a smooth transition. Even with glued up rocker slices, glue lines mike it tricky to get a nice smooth curve.
wont the rails be hard to shape, with that glue seam running through it?
I ended up using spray foam to fill the void. Once it’s shaped I’ll go over it with an epoxy foam dust slurry. I know a lot of guys use guitar string for the Hotwire, I used thicker gauge wire and I’m wondering if that played a role.
im hoping to get this shaped tomorrow, so I’ll find out then if the rails suck to shape or not.
I second StoneB.
I wait until I’d be about done shaping before messing with filling in the gaps - the bigger the gap, the drier the putty mix. I’ve done second, probably even third coats…
Considering you’re gonna lam something, wood/or?, over the blank, as you mentioned looks are a non-consideration.
Post more pics as you go (writes the lazy ol’ kook, who don’t post many pics…) Ha!
The rails weren’t too bad to shape. After planing, I used a screen and would have to sand the glue line down carefully a few times because it was protruding past the foam.
A blank cut from a solid piece would be easier, but the glue seam was also not inconvenient enough for me to not do it this way again in the future. Blank is still rough sanded but you can see the glue line in the rails.
I use tape along the edge to hold the pieces together while hot wiring, then glue it after. Glue it so it does not get to the edge of the blank so shaping the rails is easier. Even with a small amount of glue in the center of the blank the glued joint is usually stronger than the foam.
“Glued joint is usually stronger than the foam”; True.
Careful with those Hotwire foam fumes. Especially with PU.
All the best
I used a box fan to blow the fumes out while hotwiring. Nasty stuff.