The more we learn about a products capabilities, the more we realize there is no short answer when asked about products. As you know, painting contractors can apply coatings many different ways. The above photo of a hand-brushed finish was first published on Google+ and later on paint talk with some basic discussion about how it was achieved. However, the same level of finish can be accomplished using a variety of methods.
Some methods and/or primers require more labor than others, but the end-result can be identical. For example: a finish like seen above can be achieved with a certain primer and one coat of paint.
Achieving fine finishes on MDF requires a basic understanding of the substrate and how paint behaves going over it. As you are likely aware, MDF can be a sponge for whatever paint or primer is initially applied over the factory primer. Typically the end-result is less than satisfactory and more noticeable with acrylics vs oils. Once that initial step is successfully performed, the fine finishing aspects are easily obtained. If you make a mess of the first coat, you may end up with more labor than you bargained for.
January 4, 2013 The following discuss the use of Zinsser Cover Stain primer. We have replaced Cover Stain with water-base Insl-x STIX.
We paint MDF regularly, our preferred method is spraying a reduced coat of Zinsser Cover Stain oil-base primer directly over the factory MDF primer without prior sanding. The goal is to seal the porous surface with a primer fully capable of 1st coat film retention. We want the 1st coat of paint to dry on the surface. There are exceptions to pre-sanding MDF trim.
If spraying trim is not an option–or the smell of oil-base primer, Zinsser Odorless oil-base primer can be used as an alternative however Odorless does not have the same level of adhesion or gloss retention but sands easily to a powder. Something worth mentioning about a reduced primer coat is that you will lose some qualities of the product due to the reduction depending on the level of reduction.
But, you should also be aware that even though you are applying a better product over the factory primer–the factory primer is the weakest link and more reduction can be in your favor because it penetrates the factory primer deeper. No $50, $60 or $70 gal of paint is going to protect the weakest link so choose your finish wisely. I’ve seen paint release along with the factory primer on door jambs when a door near it was closed. The paint adheres to the factory primer, but the factory primer has poor adhesion to the MDF.
Seen in the photo above, we have successfully achieved a high-build wet film with the 1st coat of finish paint which will dry on the surface. Next, we want to remove any 1st coat brush application traces by sanding them out with 320-400 Abranet mesh abrasives or equivalent to a dull polished finish seen below. This sanding step can go very smooth and fast if the primer-coat was applied successfully.
Depending on the leveling properties of your finish paint of choice, paint should level-off tight and smooth. We used BEHR ULTRA Semi-Gloss for these samples. These sample boards have been passed around locally quite a bit the past month and these photos do not show-off the detail vs seeing the samples in your hand. We are certainly no strangers to producing hand brushed finishes that look like they were sprayed but ULTRA makes achieving those finishes much easier.