Epoxy lensing effect near knots in ply

Builder's Forum
1

After putting on 3 coats of epoxy I noticed several small bright spots on the deck of my Kaholo.  These spots demonstrate a lensing effect - the image of the wood below is clearly distorted.  These "lenses" (5 mm or so in dia) appear to be above tiny knots (2-3 mm dia) in the middle of the face of okoume ply pieces.   I see two "lenses" in at least two of these artifacts - one directly over the knot and one adjacent to the knot.  My best guess is that the knots absorbed more epoxy than the surrounding areas and ended up starving the fill coat of epoxy (adjacent to the wood) in the two lense locations.  I did not pre-seal the okoume panels because I did that on the underside of the deck and was not thrilled with the consistency of the coating.

I would like to drill into these voids (if these are indeed voids) and fill them with epoxy if it is likely to go well, but I'm also leery of causing damage to the plywood in a very obvious location if I drill too deep (though damage would be mininal since I'd use a tiny drill bit - maybe 1/16").  Can I be confident that these are voids and/or that it's wise to try to fill them?  The only thing that gives me pause is that these are not obvious spherical, bubble-like voids like I've seen in the past.  It looks ike they are filled and that the refractive index is just locally different, but that seems implausible.  I'm almost certain that I stirred all my batches for 120+ seconds and had good ratios, and I've confirmed that all 4 coats of epoxy have gotten at least tacky-dry.

2

I've seen this effect over knots on my boats, too. It happens because the knot is an area of end grain. It sucks up the epoxy into the space between the wood fibers and forms light pipes that have optical effects. Think of the sparkly, speckled gold layers of the coaming spacer stack, for example.

This is totally normal and there should be no voids. if there is a void, it is most likely the result of outgassing from the knot, but if you're taking the standard precautions against outgassing (applying epoxy at day's end so that the wood is cooling down instead of warming up, applying a skim coat and lightly sanding it to get rid of any bubbles, etc.) it shouldn't happen. Simple sanding will take care of any true voids.

Normal epoxy application techniques should prevent any depressions from forming. If they do form, subsequent coats of epoxy will fill them. So the takeaway is - don't worry, be happy. They're a normal part of the build process. Little decorative jewels that form naturally and proclaim that your boat is made from a once-living material instead of sheets of molded oil.

Laszlo