How To Paint MDF And Get Smooth Edges

MDF is made of compressed wood fibers, wax and resin. It’s strong, dense and flat so is a great material to choose for cabinets and built-ins that you plan on painting. The wax and resin on the surface protect the wood fibers from absorbing the moisture in water based primer/paint.

The cut edges have exposed wood fibers that will absorb moisture when using a water based finishes creating a really bumpy texture. This is especially true if you route a profile onto the edge, cutting and exposing an even larger surface area

How to Paint MDF

There are a few different ways to deal with this in order to get smooth edges.

Use an oil based primer. (No water for the wood fibers to absorb, no raised bumps.)
Cover the edges with joint compound and sand smooth before you paint. (I don’t do this as I think it’s too many extra steps…but it’s an option.)
Go ahead and prime the entire piece, edges and all with water based primer and let those fibers swell. (My preferred method.)

When the primer is dry, take a sanding sponge and knock it down. It doesn’t require much effort, just sand over the little bumps until you have a silky smooth edge.

If you used a LOT of elbow grease when sanding and re-expose more fibers so you get more bumps when you paint, it should take very little effort to knock it down before you do a second coat of paint, or touch up that area. I’ve never had that happen though. There is generally enough primer still coating the MDF after the sanding to protect the fibers from the moisture in the paint.

(My CURRENT preferred Primer for MDF is Sherwin Williams “All Purpose Water Based Primer”.)

*Important Note: If the edge of your MDF has any saw marks, make sure you sand those off before you paint because the paint will only accentuate the flaws.*

Did you find this tip helpful? You might also like these other Painting Tips!

18 Comments

Hi thanks so much for the post. This is first attempt. I have used Zinsser 123 and yes got lots of bumps. Do you use a very fine sandpaper. I have 40/70/ 100 grit in my pack frim Wickes shoukd I use the finest 100??
Thank you
Nicki

I am getting ready to tackle my first closet built ins and your whole site has given me SO much help and guidance! I am so glad you’re here and easily searchable!

Rena, I offered 3 different ways to achieve smooth edges. Option #3 is my preferred method but there are other ways to do it.

Im confused. First you say: “1. Use an oil based primer. (No water for the wood fibers to absorb, no raised bumps.)”
But then you say to use a water based primer. Which is it??

Thanks for the help!