Thread: Finishing Mitre Box Shelf

An issue you'll have with plywood is the grain being visible through the paint. Some people don't mind it, but it can look pretty average. You can use a grain filler first in all the areas to be painted white to minimize/eliminate this effect.

As for finishing order, it's kind of up to you. Finishing the parts before assembly will be a lot easier, just be diligent about keeping finish out of the to-be-glued areas. A good quality painters masking tape won't leave residue behind that will affect glue up. The Timber Protect calls itself a varnish but it's undoubtedly a water based poly, so it won't have a yellowish tint or yellow over time. Just pointing this out because it would probably be better to use the Timber Protect product over the entire shelf unit once the white paint has cured for a few days. Normal latex paint doesn't wear too well. An added bonus to gluing after finishing is that any glue squeeze out is super easy to clean up.

If you do finish before glue up, also keep in mind that finishes that are dry aren't necessarily cured and at their hardest. Water based poly will take about a week to cure, so if you glue up before full cure, be gentle. General rule is if you can smell it, it's still curing.