Finishing the underside of a desk

[Wayne Hendrix]

I am making some simple desks/tables for me to study on and for my wife's craftroom. The legs are 2x4s that will be painted and I am planning on using oak veneered plywood for the tops with some kind of film finish (most likely wipe on poly) for durability. Do I need to put a couple layers of finish on the underside of the plywood to keep the tops from warping?

[Kent A Bathurst]

I would - for exactly the reason you mention.

FWIW - I'd also put down a light coat of dewaxed shellac first - it'll help highlight the grain and even out the varnish absorption. Zinsser Seal Coat shellac mixed 50/50 with denatured alcohol, applied with a lint-free rag or padding cloth. But - that's just me - I put on a shellac seal coat on nearly everything.

[Jamie Buxton]

Film finishes don't really cut down on the transfer of atmospheric water in and out of wood. So finishing the underside of a desk won't have any effect on warpage due to that. Fortunately, because of the crossing plies in plywood, it doesn't change dimensions due to wood expansion or contraction. If it is flat when you build the desk, it will stay flat in service.

[Scott Holmes]

The unfinished side can and will absorb moisture MUCH faster than the finished side. But as noted with plywood it's not as big a deal.

[Wayne Hendrix]

FWIW - I'd also put down a light coat of dewaxed shellac first - it'll help highlight the grain and even out the varnish absorption. Zinsser Seal Coat shellac mixed 50/50 with denatured alcohol, applied with a lint-free rag or padding cloth. But - that's just me - I put on a shellac seal coat on nearly everything.

That was actually the plan.


Film finishes don't really cut down on the transfer of atmospheric water in and out of wood. So finishing the underside of a desk won't have any effect on warpage due to that. Fortunately, because of the crossing plies in plywood, it doesn't change dimensions due to wood expansion or contraction. If it is flat when you build the desk, it will stay flat in service.


The unfinished side can and will absorb moisture MUCH faster than the finished side. But as noted with plywood it's not as big a deal.

Thanks guys, that is exactly what I was wondering.