Deck Delamination / Core Problems

[ebb]

Don't know that you need to scarf anything, if you are using the word in its traditional way.

Suppose you could tilt the circular saw at 40/45 degrees to cut out the pieces so that if you are going to replace the original deck the pieces could be glued back like lids. However, the top skin of the deck is 1/8" maybe a little more if you're lucky. Any cut at any angle with a circular blade would cut more material away than the slant. IE the piece of deck/lid would be smaller than any hole you can cut. A grinder would be less accurate, unless you're thinking of using a dremel-tool.

I believe a straight 90 degree cut with a small circular saw and carbide blade set at a known depth would give you more control and accuracy. Use the grinder to vacate the tunafish - VERY careful not to grind thru the inner skin. Bedding the balsa in epoxy and epoxy gel (Epoxy, fumed silica, chopped strand*) will give you a strong deck without worrying about scarfing anything.

You may end up laminating your own deck skin back on top - rather than glueing the 'lids' back on. Conceivably it is stronger and more unified to laminate new deck back on top of the new core. Because you can marry it better to the remaing deck. However, it is conceivably easier to glue the deck pieces back on because you get an instant register with the remaining deck structure.

With the 'lid' method, after they're back on and the epoxy is set, you could grind a mild dip/depression around all the seams, three or four inches wide across the seam and fill it with strips of glass cloth and epoxy. Narrower strips in the bottom, with the next layer using wider strips. You'll only get maybe two/ three layers with the top one nearly grinded off for flush. This ought to graft the new work with the old pretty good.

With all new top laminate I would feather on to remaining deck by grinding a 'slope' on it.
This is what you meant by scrafing, I think.
It's not much, as the deck skin is so thin -just enuf for one or two layers of six or eight oz cloth to lap onto it. But with enuf buildup to grind the join down flush. Conceivably this is the stronger method. But I think it's a toss-up.

AND I always say this:
With work like this use only 100% solids laminating epoxy. Your supplier should tell you that it is NON-blushing and has so solvents or extenders in it. A great privilege of no-blush is that it will allow you to stop work and continue later without the penalty of washing and often without prep.
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*because the deck is horizontal, you need to thicken the epoxy filler only a little, just enough to control it. It should still flow so that it fills all voids and fills the baltec as well. Butter all pieces on all sides. Prefered method is to wet down/soak all surfaces with straight epoxy first, then butter. To avoid voids: You may find that drilling (for neatness) some holes in the center of panels, or where you know you have a depression to fill, that when you press the panel in its place the extra glue has a path to squeeze out like a relief valve.

Balsa with epoxy, imco, is as good if not better than expensive pvc foam for our deck restoration. Like you say, if you isolate it from thru fastenings, etc it'll last. The above method would isolate the balsa extremely well. Epoxy is a good waterproofer - and if you urethane the deck, whatz gonna happen?? And each panel is isolated so any water migration could not be a problem in the future. Some boats like 338, knock on wood, still have good decks after all these decades. Done right, new balsa composit should last a half a century! You know, like THREE generations!!
Sorry. Hope some of this diffuse stuff is usefull.