Digging in the deck

[ebb]

Ayedunknow. Can see how many find my words eye-glazers.
I wouldn't have poured in plain epoxy to try to fill the holes.

I would have cut disks of Xmatt and/or fiberglass cloth and laid them in stacked like pancakes and then capped the stack with the well buttered disk of skin.

the butter is epoxy mixed with Cabosil or alternative. The butter can be strengthened with chopped strand, which is usually 1/4" fiberglass pieces you buy by the pound or jar.

I would have prepared the holes by scrapping out the rotted balsa (with a Bacho tri-angle carbide scraper) and discarding the stuff.
I would then excavate slightly under the rim of each hole.
I would then have inserted a disk of pvc foam.
But as an alternative I could build up the required 3/8" with rounds of Fiberglass.
I would have made sure those rounds were saturate with liquid epoxy.
I would have finished each hole replacing the disk of skin that was originally removed with the holesaw.
Because the liquid epoxy can find its way into a rotted core I would have stuffed chopped strand strengthened epoxy gel into any visible space.
There may have been caves in the balsa around the rim of each hole. I would have pushed epoxy gel with chopped strand into them. I then would have laid in the rounds of fabric or pvc and capped with the disk of skin.

After the holes were filled and hard I would tap the parts of the rotted deck that were not disked out with the holesaw. If I found hollows (dull sound) I would drill in3/8" holes into them and inject them with liquid epoxy. If the liquid epoxy did not top off, I would inject epoxy gel into the drill holes until no more goes in.

Would continue this drill and fill process until no more epoxy goes in and there are no more dull hollow sounds when tapped.

Pouring in liquid epoxy into a space in an attempt to fill the space is not considered a good idea.
If the space is large and the epoxy is there in large quantity the exothemal reaction can get very hot. The area around the epoxy can get distorted, even burn, and the epoxy will boil, get frothy, and become useless..

Imco the solid epoxy fill you have does not compromise the small area you worked on. Laminating epoxy, being very thin, is formulated to be used with fiberglass and other fabrics. It also makes great fillets and installation gel when mixed with fillers like fumed silica, glass and plastic spheres and milled glass. The epoxy in itself is brittle when set and really needs to be married with the stuff it is designed for.

If you had wet out your holes with liquid epoxy -
then filled the required interstice with epoxy gel (in place of where epoxy saturated glass rounds OR pvc would have gone -
Then capped with the original top skin disk WELL BUTTERED WITH EPOXY GEL.. that could have flown.



EPOXY GEL
You need Part A and Part B epoxy to mix together. It should be the best epoxy available.
You need fumed silica to mix into the Part A - Part B mixture.
You make your liquid and fold in the Cabocil until it starts thickening.
You control the thickness with how much of the powder you mix in.
It can be quite thin but still have some body to it - or very thick and very stiff. There is a happy medium.

Epoxy blended with fumed silica is stronger than plain epoxy.
If you need extra strength: to this gell you add milled fiberglass pieces.
You can add too much and get a hairy goop. You use this stuff to give the epoxy gel some GRAIN (as in wood grain), some structure - because plain hard epoxy is brittle.
And plain hard gelled epoxy, while very strong, gets much stronger with the addition of a little 1/4" chopped strand. It becomes 'structural'. And nearly impossible to break - or to sand - so don't build it up.

[I have learned it 's easier to fill mild hollows and imperfections with easy to sand fairing compound. The one West System product I can recommend is their 407 fairing filler which you mix with your (NOT West System's) laminating epoxy to produce a chocolate colored surface you can sand. You can use this stuff under the waterline. There is another material: 410, but this compound should be used inside only.]

You can't inject epoxy gel that has chopped strand in it. The gell will be adequate in the core repair. Inject it to fill hollows. It also will naturally fill all your drill holes.

Making gel allows you to fill tilted decks, vertical walls and holes overhead like in your liner in the boat.

Damp balsa doesn't make a good thickener. Any pieces of ANY material (even glass micro-spheres you can use to make fairing compound with) when mixed into epoxy liquid will fall out. It'll sag. You need a matrix like Cabosi to make a gell to hold added materials like balsa in suspension.
You need the Cabosil to make a filler that won't move before it can set. You need the Cabosil in your fiberglass kit. Liquid epoxy is generally only used to wet out laminations of fabric.*
If you want to make a glue as for plywood, or backing blocks, or fillets you have to add the fumed silica.

This still doesn't read CLEAR, but I really hope it is useful.
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*Laminating epoxy makes a great sealer and grain filler for mahogany that will be finished bright.