Sealing Ultralight MDF Shop Jigs

Ideas for quick sealing of MDF. January 14, 2009

We use ultralight MDF for a lot of shop jigs. It’s convenient, flat, and stable. It is however a real pain to seal. We don't need a finish grade coating, just a sealant for long term stability (and so spilled coffee doesn't ruin the jig).

Does anyone have any suggestions - especially on the "end grain" cuts. We currently do a three coat water base poly with sanding and that’s way too much work. It takes much longer than building the jig.

Forum Responses
(Finishing Forum)
From contributor A:
Bull's Eye clear shellac.

From the original questioner:
Shellac was my first thought, but the shellac sucks right in and takes more coats to seal than the water.

From contributor R:
Have you tried Glue size? Wood glue slightly thinned with water.

From contributor J:
One heavy coat of lacquer vinyl sealer will seal MDF.

From contributor G:
If it doesn't have to look pretty, one coat of heavy bodied primer, aggressively sanded back and one topcoat of whatever you like.

From contributor I:
If you can machine sand the end grain cuts to 400 grit or higher, they should seal much better for you.

From contributor C:
I have sealed a lot of MDF edges and tried everything. I sand with 100 grit then flood Bullseye dewaxed shellac on with a bit of lamb’s wool until it doesn’t want any more. For me sanding finer before doing this is a waste of sandpaper and time. Sand the result with 150 and you are ready for any primer or topcoat.