varnish question

[Mark Marino]

I've been trying to varnish my mandolin build, after applying a light sealer coat of shellac as has been recommended. The issue I'm having is that there are razor thin cracks/depressions where the binding meets the wood, and even after a few heavy and many light coats of varnish, those cracks are not filling. Any recommendations to get a seamless finish? (I'm using waterlux urethane this time as it stays clear, but prior builds I'd used other oil varnish with the same issue- would be nice to overcome that on this build) thanks!

[sunburst]

Can you get a good picture? Is it a crack or just a depression? Do you know what caused it? Is it from scraping the binding? Poor adhesion of binding to wood?

[Mark Marino]

Can you get a good picture? Is it a crack or just a depression? Do you know what caused it? Is it from scraping the binding? Poor adhesion of binding to wood?

Trying to get a picture that would have it show up but no luck so far. Its basically a razor thin line where binding meets wood, likely I didn't get it tight enough as its on the sides and not the top-back.

[sunburst]

If it's a hairline it's probably a poor fit of the binding to the channel. It won't help this time, but a slight bevel to the bottom edge of the binding, so that the outside edge is the tight edge and the edge at the corner of the channel is the potentialy loose edge, helps with that. I also scrape the sharp, square edge of the binding so that there is no interference in the corner.

Now that it is done, I suppose you need to fill it with something... something clear perhaps, or something the color of the wood... clear is probably easier.
You might try scraping the varnish away along the hairline and filling it with epoxy. That should fill the crack, not shrink, and adhere well to the (re)finish over it.

[Mark Marino]

Thanks John- advice much appreciated. I was thinking there might be something I could do to get the varnish to flow better but will try the filling technique. Cracks are so small I'll start with crazy glue on a small section (non gel) and go from there. Great suggestion about beveling the inner corner of binding- I can see that really aiding in a tight fit.