Backyard Renegade ) writes:

The problem is that inner layer. Like William said, it is like rods
and frequently has voids that run full length or nearly, hidden under
the skins. Many times these voids do not show up until you cut, sand,
or snap the piece putting it in. Anyway, the fact that the center is
harder wood, and frequently void filled, it makes the softer outer
skins prone to snapping, much like scoring a tile or piece of glass
then bending it...
Scotty

the voids are easy to find. you take the plywood into a dark room and run
a reading lamp over the surface while looking at the other side. any voids
show up where the light shines through the thin suface layer.

the voids are easy to fill. drill small holes though the face ply and pump
in clauk with a calking gun. I prefer to pump in PL Premium polyurethane
construction adhesive to fill the voids. You have to put a piece of tape
over the wood and drill through it to keep the goop from getting on the wood.

I've used the same drill-and-pump technique to repair a split plywood
daggerboard. Once the goop was pumped into the spit layers the board was
wrapped in plastic and weighed down flat overnight to cure. Still
using that daggerboard.
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