The voids problem is most often mentioned when weighing the relative merits/drawbacks of Luaun plywood for small boat/dinghy building.
These are often built with long narrow panels. The voids running perpendicular to the length of the panel cause poor bends (at best) or cracks (under excessive strain).
Like any other problem, there are at least several solutions.
1. Don't buy plywood with voids.
This is OK for the guy with more dollars than sense; but not for the first-time builder, or someone wanting to build a "cheap" boat. [Is there really such a thing?]
Marine plywood usually triples or quadruples the initial costs.
2. Do what I did when building Puffin.
After carefully selecting the ONLY two perfectly voidless sheets of Luaun plywood at my Home Depot, I went home and started boatbuilding.
The panels for Puffin were cut, and to my utter shock and dismay, discovered... "Ack! Voids!".
I propped the panels up on edge, on top of two sawhorses.
Then I made duct tape funnels around the void holes, mixed epoxy, and dribbled it into the voids.
The voids ran clear through the panels. I let the epoxy drip out of the bottom so that I knew it had coated the entire length of the hole. Once it started dripping, I plugged the bottom and let the hole fill up with more epoxy. It took quite a bit more than I expected. (The epoxy was soaking into the wood surrounding the hole.)
The hole eventually filled up; bubbles welling up to the mouth of the funnel. Occasionally, I poked a piece of piano wire into the hole to encourage bubbles to the surface.
That's it. Solid plywood. No weak spots. Fair curves when bent.
The occasional voids in the frames of Albatross were treated similarly.
Copyright © 1999 Alan "Maddog!" MacBride
Most recent revision December 18, 1999