Spraying MDF (The edges)

[Jim Kountz]

Ive been trying to spray some MDF projects Im working on and the edges are killing me. I sand and sand and sand but no matter what I do they still bleed horribly and take many more coats to cover than the surfaces. Does anyone have a "recipe" for dealing with this problem? Ive tried sealing with just about everything I can think of with some results but not great. Ideas anyone?

Thanks!

Jim

[Doug Shepard]

I haven't personally tried this, but one of those tips submitted by readers to WW mags a while back advocated using automotive filler (Bondo) on MDF edges. Don't remember which mag it was in. It was just wierd enough to make it stick in my mind. I don't suppose it could hurt to try it.

[Jim Becker]

Doug is correct...you have to fill the edges. I use spackling compount, but bondo or anything else like that is just fine, too. Once filled and sanded, two coats of primer with sanding in between coats should do the job.

[Wes Bischel]

Jim,
A few other threads on this subject. I use dewaxed shellac - two coats one right after the other to soak the edges and any other surfaces that have been altered. It drys fast, and sands super smooth. Then prime and paint with finish coats.

Good luck,
Wes

http://www.sawmillcreek.org/showthread.php?t=17962

http://www.sawmillcreek.org/showthread.php?t=21188

[Norman Hitt]

One of the "Better" Cabinet shops here gets the nicest finish on MDF edges I've seen. He Routs the edges with whatever profile or roundover he wants, then IIRC, sands the edges with 320 grit but "does not wipe or blow off the sanding dust" before he shoots the sealer, then slightly sands again with 320 or 400 grit, (can't remember which), and again leaves the sanding dust on and shoots the second coat of sealer. This really seals the edges up nice and smooth, and he then lightly sands with 400, wipes it down and applies his final finish, (normally lacquer).

Note: this may not be "exactly correct" as to his procedure, but I know it's close enough that it should work.

[chris toomey]

i've read that others have used joint compound.......

[Phil Phelps]

If your going to paint MDF, here is what I've done for eons. For a hard finish, I use Bin pigmented shellac. It's alcohol base and dries fast. I use two or three coats and apply it with a Fitch brush. You'll have troube finding a Fitch, because it's used in the sign business. But a short bristle brush will do. You need to message it into the MDF, that's why spraying is a waste of product and time. I also use a flat latex wall paint, two coats and sand with 220, and then finish it. Clear shellac will work for clear finishes. Spackeling and wood fillers are too slow. Ditto for Bondo on the edge.
Use joint compound and a broad knife for the face of MDF. You'll fill the pours in one application. Just trowel on and trowel smooth. When it dries to a white haze, sand with 220 and use your primer to start the finishing procedure. Bullseye (BIN) pigmented shellac is a fantastic product if you are spraying. Also, an automotive undercoat is a good primer and builder. You could roll a latex flat paint, with an enamel roller cover, and sand with 220 between coats. The joint compound is the fastest, cheapest, and easiest way to fill the pours in the face of MDF. I can make that cheap board look like a fine car finish using this procedure.

[Jim Kountz]

Well first off let me say thanks to everyone who offered help. I really appreciate it. Filling the edges did the trick and I couldnt be happier. I was hoping I wouldnt have to go that route but what the heck it works and doesnt really add alot of time to the project in the long run right!! Thanks again everyone!

Jim