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MDF, short for ‘medium density fibreboard’, is a cheaper alternative to wood. MDF is made of wood fibres that have been combined with resin to form a fibreboard. The main surface of MDF is smooth, but the edges, which when cut expose the fibres, can be rough. It’s not difficult painting MDF, but you do need to sand between each stage to keep the edges smooth. Using an MDF primer will help achieve a great finish, as the primer stops the MDF from absorbing the paint.
Why Use MDF?
MDF (Medium Density Fiberboard) is an engineered wood that combines wax and wood fibres. Under high heat and pressure, the wax and fibres are pressed together to form MDF.
There are several benefits of using MDF, such as its smooth surface, lack of visible grain and relatively low cost.
However, as you’ll learn below, MDF is not always a great fit. For example, one major drawback is that MDF doesn’t mix well with liquids or moisture. I.e. When MDF gets wet, it will expand significantly, so, it’s best to avoid using MDF in kitchens and bathrooms or any other high humidity areas.
The table below provides more detail on the pros & cons of using MDF in your DIY projects:
Pros And Cons Of Using MDF
|Fine wood fibres give MDF a very smooth surface which is easy to paint||MDF can be hazardous when not treated properly or when cut open|
|There is no visible grain in MDF. This makes MDF great for building furniture when you don’t want to deal with pattern matching||When exposed to water, MDF can permanently change shape. Water damage risk can be mitigated by preparing the surface using an MDF primer and appropriate paint.|
|MDF is cheaper and denser than other options such as plywood||MDF is considered a ‘cheap’ and unattractive wood by many, especially when left unpainted|
What Primer Should I Use On MDF?
The MDF manufacturing process uses chemicals and adhesives that can react badly with the wrong primer. Therefore, you need to use a primer that is suitable for MDF, as this will prevent the MDF from breaking down. Poor primer choice can result in the finishing paint peeling off and looking a mess!
Never use a latex primer on MDF, as it will cause the MDF to expand and affects the texture of the material. You’ll get the same issues from using water-based primers, so make sure you avoid these types of primers at all costs. You also need to be careful with so-called ‘multi-purpose primers’.
So, what is the best primer to use on MDF? We highly recommend a solvent-based primer, ideally one that is specifically sold as an ‘MDF Primer’.
What Paint Should I Use For MDF?
As you now know, MDF and water don’t play well together. I.e. water causes the fibres of the board to rise which is hard to remedy.
In theory, painting properly primed MDF with water-based paint shouldn’t cause any damage. However, in practice, you run the risk of severely damaging your MDF.
Therefore, Oil-based paints are a much better option when you paint MDF. Beware though, oil-based paints have a much stronger odour than water-based paints. When using oil-based paints, we recommend opening your doors and windows for at least 7 hours after you’ve finished your paint job.
Latex and acrylic paints are also good options for MDF painting projects. If you’re a beginner, you’ll probably find these paints easier to use than oil-based paints. For example, you can thin latex and acrylic paints by using water, as opposed to oil-based paint, that needs paint thinner.
To find out more about thinning paint using water, check out our painting new plaster guide. In short, a ratio of around four-parts paint to one-part water will work well.
What Finish Coat Should I Use For MDF?
The last thing to consider, is what kind of finish are you after? Various types of paints offer varying levels of shine. Depending on the goal of your project, you might want to use gloss (high-shine), satinwood (medium-sheen) or eggshell (matte/no shine).
Tools & Materials Required
- MDF board
- Dust mask
- Fine grit sandpaper (120 to 220 grit)
- Soft cloth
- Paper decorator’s suit (optional)
- Filler -- drywall compound is recommended
- At least 3 paintbrushes or rollers
- Solvent-based primer
Pro Tip: Always wear the appropriate safety gear when you are handling MDF board, especially if you are sawing into it. A good fitting dust mask is essential for this project
1. Protect Yourself
MDF contains formaldehyde, so make sure your mouth is covered with a face mask. You might want to wear a paper suit (like CSI) as well. MDF fibres can be very dangerous, so take precautions as this is not something you want to breathe in.
2. Sand And Wipe MDF
MDF has a very smooth surface, but it tends to have rough, porous edges. For a smooth finish, you need to sand the edges of MDF down, but first, lightly sand the surface.
A lightly sanded surface will give the MDF board a ‘key’ that the paint can cling to. Then wipe away any dust with a soft cloth. I would avoid wetting the cloth as MDF sucks up water, which causes swelling.
The DIY Doctor recommends using a sanding block (you can make your own by wrapping sandpaper around a block of wood) to ensure a flat sanding surface.
3. Fill MDF Edges
The rough edges of MDF need to be filled up to smooth them out. While a drywall compound is recommended, a wood filler can also be used (see video below). Apply an even layer, leave to dry, then sand again. There is a lot of sanding in this project!
4. Prime MDF
Priming the MDF board with the correct primer will stop paint from being absorbed and wasted. Use a brush or a roller that fits with the size of the MDF you are painting.
Use a solvent-based primer that specifies it is suitable for MDF. Do not use latex as it causes the wood fibres to swell. Water-based primers have the same negative effect.
5. Sand (again)
Once the primer is dry, sand the MDF again. Use a light touch. You want a smooth surface, but without taking off the primer. You might need to prime and sand a second time to achieve this.
Rejoice, for you finally get to paint! Use an oil-based paint so it doesn’t interact with the primer. Take a clean brush or roller (i.e. NOT the one you used for priming), dip it in your paint and apply to the MDF. Leave to dry.
Again, you might need a second or even a third coat. Moreover, if there are any rough patches, guess what? You guessed it, sand them down! I promise this post is not sponsored by sandpaper manufacturers.
7. Seal MDF
For the last step, take a third, clean brush and apply a sealant. The sealant can be any type of wax or varnish compatible with your paint. Leave to dry and then admire your handiwork. No sanding for this step!
Pro Tip: YouTuber Charlie DIYte provides a good tutorial below on his method for painting MDF. It differs slightly from my way, but the end result looks just as good
So now you know that the secret to painting MDF is to sand, sand, and sand again. MDF is a cheap and versatile material, and if you protect yourself from potentially harmful dust, it is an excellent choice for projects in your home.