Finishing One-Piece MDF Doors

Profiled areas of MDF doors require additional labor and care for best finish results. Here's advice. June 18, 2013

I have a kitchen full of these to finish. The recessed panel area isnít the smoothest with marks left from the CNC. Any tips of a quick way to level/fill the machined area. I will be using Valspar post cat primer, followed by a CV topcoat. I was thinking to give it a quick sand, spray a generous coat on the panel area, sand it back really well to level, and then prime the whole door, then topcoat. Iím looking for tips or recommendations for those of you who work with one piece MDF doors frequently.

Forum Responses
(Finishing Forum)
From contributor N:
I had the same issue a few years back. Now I use a flex trim hand sander with 320 grit paper on it. The fingers in the paper drop right down in the panels and buffs everything shut. It saves me a ton of time and material cost on my primer. Hope this helps.

From contributor F:
Any cut and routed areas are going to be rougher on MDF, some are worse than others due things like poor MDF quality or the skill and technique of the person doing the routing. A dull bit and a rushed job will make for a very poor surface. The Valspar CV primer will work well for this but don't make the mistake of flooding on the first coat, this just makes take longer to dry and therefore harder to sand if it's not fully cured.

This is going to be true with pretty much any brand of primer - SW, Valspar, MLC, you name it, the thicker it goes on the harder it will be to sand. Start by sanding the bare routed areas first with nothing rougher than 320 grit if they are in as bad shape, or even incorporate a wash coat of vinyl sealer first then scuff with 320-400 before priming. Resist the urge to use rougher sandpaper because this will just tear out more fragments, making more pin holes to fill with the primer.

Then apply the CV primer in a normal 3-4 mil wet thickness. One or two coats applied his way with a scuff sanding between coats are almost always going to provide a better surface to finish than trying to do it all in one thick fire hosed coat. This may seem counter intuitive because you are applying more coats but sanding a thick coat of CV on a poorly prepped surface is not fun and not very productive to either time or quality.

From contributor M:

They are done now. I sanded the panels, sprayed a good heavy coat on the panel area (about 5 mil), and let dry overnight. I used a 1/4 sheet sander to level and scrub back almost to the raw MDF again. Two coats of primer, one coat of clear, and they look great.