Firstly, can the red devil spackle...I mean...PLASTER!!!??? Not.
I don't do any installs straight up against EPS, whatever the density. Its a liability. High density inserts every time.
You should be able to lever up the delammed bits a little with a blade and get resin in there. I'd do that separate from the mix you do the boxes, so you get a chance to weight down the delam. Plasic over the spot and a padded brick...
Yer, I was reading through some of the archives and someone (cant remember who) said the he uses a syringe to push resin through a straw. Sounds like a good idea as you can flatten out the end of the straw so you dont have to lift and cause further delam.
I will do the epoxy/ballon mix next time
I think that inserts may be a think of the future for me. Been thinking about making up a couple of jigs. One for the insert and one for the hole to fit the inserts. If I can get it right, it should be a perfect fit every time.
I'm with Speedneedle about the inserts. I never set boxes or plugs into straight EPS. I have set plugs into VH EPS and i was abit worried about heat etc. Any type of HD foam will do corecell, d cell, klegecell etc. even offcuts of surfblanks red foam.
Qcell and epoxy is the best bet for sealing. When I use that and set boxes or plugs the foam comes away with the glass from the routed section.