As a professional decorator, it’s safe to say I’ve painted a lot of MDF over the years. This blog is my guide to painting MDF — I’ll take you through the process and share a few product recommendations. Feel free to skip ahead and pick out the information you need.
Thanks to DIY SOS and a host of other TV DIY programmes, MDF has become an enormously popular material around the home, and is used for all sorts of projects from media walls to furniture, and from panelling to shelving.
It’s easy to see why; MDF (Medium Density Fibreboard) is a “uniform” product without defects like knots which you’d find in natural wood. It’s readily available in a range of thicknesses, is affordable and easy to cut and fix together. So, it’s very easy to build things from, but not so easy to paint.
The problem is that the edges are extremely porous and tend to soak up paint, so instead of a nice smooth finish you can end up with a rough “fluffy” texture, uneven coverage and often brown stains leaching through your paint.
This is easier to understand when you know how MDF is made; the faces are exposed to extremes of heat and pressure during the manufacturing process, which is designed to produce that uniform surface which makes MDF so desirable.
The cut edges, on the other hand, are like the frayed ends of thousands of wood fibres; they’re not uniform, they’re not smooth, and they’re highly absorbent, and that’s why they need different treatment to the faces.
If you simply paint an MDF sheet without the proper preparation, you will probably have two different results; while the super-smooth faces may be OK, on the edges the paint will soak in too much, almost disappearing, but leaving behind an unwanted “fluffy” surface, often with a brownish stain showing.
With MDF still as popular as ever (probably more so with the current popularity of colour-drenched media walls and panelling), professional decorators like myself have had to find solutions to this problem. In this blog, I’m going to take you through the tools and materials you will need, and a step-by-step guide on how to successfully paint MDF to achieve a smooth, professional finish. It’s worth reading this in conjunction with our blog “The Best Paint for MDF” for the best results.
Tools & Materials Needed for Painting MDF
- Dust sheets
- Sandpaper (120 – 240 grit) or dustless sanding set-up
- Dust mask
- Tack cloths
- Primer
- Decorators Caulk
- Wood filler
- Topcoat paint
- Paint brushes
- 4” mini roller
Painting MDF – Step-by-Step Guide
Prepare your work area
Move any movable furniture, ornaments etc out of the way to avoid paint splashes, and cover the floor and any remaining furniture with dust sheets.
Open windows to provide ventilation and wear a dust mask when working with MDF. (MDF is made from roughly 80% wood “pulp”, held together with resin – this resin is usually urea-formaldehyde, which is known to be an irritant and believed to be carcinogenic, so you don’t really want to be breathing it in).
Apply a coat of primer
For large flat areas you can use a mini-roller for this; either a foam one for shellac- or oil-based primers, or a microfibre roller for water-based primers. For small areas, awkward corners and the edges, use a suitable brush. Allow the primer to dry.
Sand the surfaces
Lightly sand the flat faces . Pay more attention to the fluffy edges – sand thoroughly to get them as smooth as possible. Remove as much dust as possible with a vacuum and/or tack cloth.
Fill
Assuming you are painting something that is already assembled (e.g. cabinet doors, panelling), caulk any gaps/joints, and fill any nail or screw holes with a good quality wood filler, like HB42 Ultimate. Priming before filling highlights some of these imperfections which might not have been visible before priming. Allow the filler to set properly.
Sand
Sand the wood filler smooth. Sand the MDF again, paying close attention to the edges – the primer will have soaked into the wood fibres, causing them to swell and creating a rough “fluffy” surface. Sand this as smooth as you can, and as before, remove dust with a tack cloth.
Caulk
Run a small bead of caulk where needed.
Prime again where needed
Re-apply primer to the edges, and spot prime the filler. Leave the primer to dry.
Sand again, prime again
You may need to repeat the process several times on the edges until they are really smooth. Finish with a light sand and a wipe over with a tack cloth.
Apply your topcoats
Again, using a suitable brush and roller (foam for oil-based paints, microfibre for water-based). Unlike natural wood, there is no grain to work with, but I always roll in the same direction and then lay off with a brush afterwards. Apply thin, even coats, and follow the manufacturer’s instructions regarding drying times between coats.
It really is that simple – the secret to smooth edges is to just keep priming and sanding them, using progressively finer sandpaper, until you have the result you want. Each time you apply the primer, the ends of the wood fibres absorb some of it and swell, creating that rough feel, but with each subsequent application they gradually become “sealed” and the problem is solved. Make sure you remove as much dust as possible after each time you sand, as dust in your paint can ruin the finish you are trying to achieve.
The Best Tools for Painting MDF
Rollers
If you have large, flat “faces” of MDF to paint, using a mini roller will allow you to get paint on faster and more evenly. For oil-based paint, a good quality foam roller is best; you will have to throw the sleeve away when you’ve finished, it’s not worth trying to get them clean. For water-based primers and paints, I really like Axus Décor’s Pureflow Ultra roller sleeves – they give a very fine finish. Click here to see online prices.
Brushes
For oil-based topcoats a natural bristle brush is best, like Corona’s “Griffin”, simply because the bristles won’t clog when using them.
For water-based paint, I love my Axus Décor Silk Cutter 1½” brush; it’s angled to help get into awkward corners, and the flagged tips are great for laying off to give you a super smooth finish. Click here to see online prices.
Primers and paints
To some extent this is down to personal preference, but if you want my thoughts and recommendations, please have a read of our separate blog on the subject “The Best paints for MDF”.
FAQs
If it’s properly painted, can MDF be used outside?
No, I really wouldn’t. Even when it’s been thoroughly sealed and painted, MDF is still a really absorbent material, and will soak up rainwater and expand. Once it’s expanded, it won’t shrink back to its original shape. I wouldn’t even use MDF inside in a bathroom personally – take a look at this piece of MDF skirting which was located right next to a shower door. Every time someone got out the shower, it soaked up water splashes from the floor.
Can you paint MDF without priming first?
No, because MDF is very porous and will absorb a lot of your paint. The flat faces will probably look uneven as a result, and the edges will be rough or “fluffy”. Additionally, you will probably have brown stains showing through your paint. Priming is absolutely essential to achieve a good result.
I want to keep my MDF its “natural” colour. How do I prime it?
There are specific MDF sealers available for just this type of situation, which are clear rather than white. A good example is Rustins Quick Drying MDF Clear Sealer (available online here). Follow the process as described above, using the clear sealer in place of primer, and a clear varnish such as Smith & Rodger Rocktop in place of the topcoats of paint.
Can I paint MDF with emulsion?
Yes you can, if you prime it properly first, as described above. I’d recommend a durable emulsion like Johnstone’s Cleanable Matt, or Tikkurila Optiva 5, for the best results.
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