Ola Senor!
I’ve had the same woes with glue-ups before; which glue to use, how will I cut through it and the resulting highs and lows (psychologically AND physically…on the blank that is) of this endeavor. I’ve also had two boards delam at sh*tty glue-up spots in the core, so I DO think it’s important that you have good adhesion there, especially if your board is going to withstand any elevated temperatures.
There’s a couple of ways around ever encountering glue in your lay-up; One method is to have both your rocker templates and outline templates handy; trace them out on your sheets of foam; both for the outline and for the profile, before you apply any glue. What you can then do is trace your templates on to the foam, giving you an area to spread your glue that you will not contact when you hotwire. Horizontal lines across the sheet from where your rocker template connects the sheet intersection will give you these boundaries. Sand the region between these lines down with some 60 or 100 grit to give the foam something to bite in to; spary the other sheet (that you’ve also sanded lightly) with a bit of water and you’re off to the races.
The other approach is one that you’ve already hinted at and I’ve found to be the best option; Lay up a rocker bed separate from the core manufacturing step. Easy peasy; you can put one together with scrap pieces of foam that you have left around from other projects; all you need to cut is that actual bottom; no deck cut required. Once you’ve got this taken care of, you’re laughing; grab a couple of sheets of foam such that the additive thickness will be enough for your board +~1/2". Trace the outline of the board on to the sheets; top and bottom, on both of them. Sand the inside area of this outline lightly. Take a small amount of epoxy and squeegee it over the outlined region. Place that sheet on your rockerbed; even use a piece of tape to insure you’ve got it in the right location. Then lay the next sheet overtop; tape it to the first. Now you’ve got your two sheets on top of your rockerbed. Slip the sheets, + rockerbed into the vac-bag and pump that sucker; check that nothing has slipped too far…go drink a beer and get a good nights sleep.
Next day, peel off the bag. What you should now have is the two sheets glued together, but the curve will be locked in to some degree. What you can NOW do is weight that puppy down onto the rockerbed again and set up your profile templates for hotwiring. You SHOULD be able to find a way to place them such that the seam between the two sheets exits exactly (or very close to) the tip and tail (better a seam on the deck than on the bottom). Screw the templates in to the foam and hotwire away. You should now have a blank with some (probably not all) of the rocker pre-locked. Because you’ve traced your outline already, you should be able to just take marking from the offcuts for tip and tail position, trace once more and cut the outline for your blank. Done.
Next is actual shaping. You can go a bunch of ways here; Benny1 would suggest that you shape the bottom, then vac on the bottom skin (if you’re sandwiching). Again, go back to your rockerbed to do this. Now that you have the glue-layer in the middle and a sandwich on the bottom, your rocker is locked, the board is pretrty stiff and you’re good to go with the rest of your shaping.
So, basically, that was just a really longwinded way of saying go buy some more foam and use the rockerbed that you just painstakingly made to save yourself having to deal with glu-lines in the shaping process and delams in the finished product. Glass, epoxy, finboxes and/or fins are the expensive part; the foam is not. Better to scrap and start over than finish a project that is doomed from step 1.
HTH
