Painting MDF Cabinet Doors

Some finishes raise the fibers on MDF (especially at machined profiles), creating sanding and recoat headaches. Here's advice on minimizing the problem. October 19, 2014

Question (WOODWEB Member) :
Iím painting some cabinet doors with MDF panels, I notice that there seems to be fibers raised when after spraying a waterborne finish in them, prior to spraying they were smooth to the touch and lightly sanded. I sanded after the first coat and the fibers seemed to come back - not all but many since this is my first experience with MDF is this the way it is? Or can I do something to prevent this? It seems I will have to spray/sand many coats to get it smooth as maple.

Forum Responses
(Finishing Forum)
From contributor H:
Don't use a water born finish for the first coat. Seal it with something else. I'd use shellac or a vinyl sealer.

From the original questioner:
Is the shellac full strength or cut?

From contributor H:
I buy it at the Sherwin Williams store (pre-mixed) and use it straight out of the can.

From contributor C:
Painting MDF isn't fast, easy or cheap. Most don't price out the paint jobs enough and learn the hard way.

From contributor T:
Zinsser Bins works well. Prime the panels before assembly of doors.

From contributor N:
I'm with Contributor T. Pigmented shellac is a good way to go. It dries fast, sands great and you can spray it at low temps. On the down side, it does take a bit of time to clean thoroughly out of the spray equipment.

From contributor J:
Zinser now makes a synthetic shellac that is more compatible with h20 spray equipment.

From contributor F:
It's the machined areas of the MDF that give you the headaches. Not all MDF is created equal, some are higher density than others and the higher the density, the less fiber tear out there is when the profiles are machined. The skill and quality of the people and equipment doing the machining also is a big issue because MDF that is rushed through a shaper with dull bits will have horrible quality. So putting some time into finding the right doors helps a lot.

That being said, things that you can do to make life easier for yourself is don't sand the routed areas with too rough a grit when prepping. Anything rougher than 180 or some even say 220 will just pull more fibers out, making more fuzz and pinholes to fill. Solvent base vinyl sealer on the routed and cut areas works well, scuff it with 320 grit before priming. Then don't flood your primer coats on either. Surrender to the fact that two medium primer coats are better than one heavy primer coat.

From Contributor W:
My paint rep told me 320 or finer for MDF. Since that day I never had trouble again.

From contributor S:
We use plasti prime by chemcraft and it fills really nice.

From the original questioner:
Thanks guys, itís been a learning experience I could have done without, but none the less Iím wiser for it. I ended up spraying many coats and sanding between each coat with 320. I likely sanded off more than I put down, but I got a smooth finish. Iím not planning on getting MDF panels again unless I can get a better finishing schedule. MDF took me much too long to complete when compared to maple.

From contributor T:
It doesn't appear to be a learning experience so if you continued to do what you were doing expecting a different result. From what I read, it appears your finish schedule was paint, sand paint, sand paint, sand paint, sand paint. The concept I think you missed from the advice given is that you need a non-waterbased primer in-between the MDF and the paint.

From the original questioner:
Youíre correct, but I started with a waterborne primer and there is my mistake. I should have sanded 320 and sealed it, primed it and then applied the paint. Next time I will try it that way.