Medium Density Fiberboard (MDF) is a wood product made by combining fine wood fibers with wax and resin to form building panels under high temperature and pressure. MDF is a porous material. Like a sponge, it sucks up any liquid product you put on it, so it needs extra care and protection to shield it from moisture damage.
Painting a wooden structure is the fastest and most affordable way to protect it from moisture damage. However, the physical composition of MDF makes it challenging to paint; therefore, it requires a particular procedure to color it successfully. So, what steps should I follow to properly paint MDF?
Start by sealing the cut edges with wood filler or PVA glue, then apply an oil-based sanding sealer on the whole board to prevent it from sucking moisture from your paint and primer. Next, put on a solvent-based primer for added moisture protection and a good surface for the color to grip. Once the primer dries, coat the MDF with paint like you would with regular wood.
Painting MDF might not be as straight as the painting of a normal wood though it’s a doable task provided you know the right procedures and stick to them. In this article, I will discuss more on how to get the very best results while painting your Medium Density Fiberboard (MDF).
How Do You Prep MDF for Painting?
The three ways of preparing MDF for painting are sanding the surface, sealing it then applying primer. If you follow these steps and use the right products, all your MDF painting projects will come out smooth without texture or blistering.
- Sand the Surface.
MDF boards are already sanded down to a smooth finish when you buy them; however, you need to etch the surface a little with 200-grit sandpaper to improve the adhesion of coating products.
When sanding MDF, pay closer attention to the edges of the board, especially the edges you have cut because they tend to be rougher than the faces.
A good tool that you can use to sand MDF is an orbital sander. This handheld tool works best on large boards, and it is not overly aggressive, so you won’t have to worry about scrubbing off too much material from the surface.
You can also use standard handheld sandpaper, especially when preparing smaller surfaces or boards with intricate designs, allowing better process control.
If you use handheld sandpaper, I recommend that you wrap it around a sanding block instead of using your bare hands. A sanding block has a flat bottom that makes it ideal for dry sanding. Since we sand objects to level their surface, the flat side of a sanding block makes it suitable for guiding the sandpaper.
- Seal the Edges
The edges of MDF are more porous than the faces, so they absorb moisture easier. Sealing the edges is essential because it prevents the board from soaking up the paint as you apply it. Sealing the edges also gives your color a good surface to adhere to, resulting in a smooth paint job.
The best way to seal MDF edges is by using a wood filler. Add a generous amount of filler to the edges using a putty knife or your fingers, then let it dry. Afterward, sand down the edges, then wipe the board with a dry cloth to remove dust.
You can also use an oil-based sealing primer for the edges because it is thicker than regular primers. Apply a generous amount of the sealer, then once it dries out, sand the edges properly to make them smooth.
- Apply Primer.
You cannot start painting straight after sealing the edges of MDF because the board can still absorb moisture from paint. When a surface absorbs water from a paint coat, it leaves behind a “skin” layer that will peel off the surface.
Any subsequent layers you apply will stick to the skin layer instead of the board and peel off soon after the job’s done. We recommend using a primer as a barrier between the MDF and paint to remedy this. Apply two or three coats of primer to MDF, sanding gently between coats after they dry, and don’t forget to prime the cut edges
MDF is sensitive to some chemicals, so you need to be particular about the primer you use.
When painting MDF, stay away from latex and multipurpose primers because they will cause your board to swell. Instead, use solvent-based primers to provide better moisture protection without reacting with the surface.
What Is the Best Way to Finish Paint on MDF?
MDF requires constant and reliable protection against moisture to remain in good shape. So, the best way to finish paint on it is with a semi gloss or a high gloss finish. High-gloss and semi-gloss paints have higher proportions of resin than pigment, so they dry into a rigid and durable coat.
The coat resists moisture far better than other paints, making this finish ideal for MDF.
Moisture resistance aside, glossy finishes can stand up to constant scrubbing and touching; hence they are ideal for finishing MDF projects in high traffic areas of the home.
Furthermore, shiny finishes look significantly brighter and bolder than similar color tones with a lower sheen. Because of the high gloss, the light will reflect off the surface, making the colors seem more vivid, and your surface will stand out.
You can also give your MDF a flat or eggshell finish if you prefer the look, but I do not recommend it. Such finishes have more pigment than resin in their formulation; hence they aren’t as durable as their glossy counterparts.
Their inability to keep away moisture or withstand mechanical damages puts them at the bottom of the list of coating products that work best on MDF.
Can I Paint Straight Over MDF?
You cannot paint straight over MDF in its “raw” form because the paint will react with the board causing it to flare up, thus loosening some of the wood fibers in the process. And, as the paint dries, it will harden over the loose particles, leaving a rough and textured paint job.
It is best to put on at least one coat of primer on MDF before applying paint on it to prevent direct contact of the product with the board.
If you’re unsure about the correct way of priming MDF or the product to use, you can purchase pre-primed MDF boards from your local store.
Pre-primed MDF arrives with white primer already applied and sanded, so all you have to do is put on the paint of your choice and finish it as you desire. Pre-primed MDF is a popular choice among woodworkers, especially novice DIY enthusiasts who don’t know much about MDF.
Not only does it shorten the time you’d take to finish your project, but it also increases the chances of achieving a better-looking paint job than if you’d prepared and primed the board yourself.
Most companies that sell pre-primed MDF use spray-on primers, which are best to achieve a perfectly even coat and a blemish-free surface that is ready to paint.
Even though pre-primed MDF makes painting faster and easier, they tend to be super expensive. So if you’re working with tight finances, I recommend preparing and priming MDF boards yourself to cut expenses.
Do You Need to Seal MDF Before Painting?
Yes! MDF is a durable product, but exposure to moisture can cause irreparable damages like swelling and warping, and there’s no way of salvaging such damages. So, it is best to seal all sides of MDF before painting to prevent moisture penetration and lengthen the service life of the building material.
A common mistake that woodworkers make is leaving MDF faces raw after sealing the edges. The usual assumption is that the faces are solid since they have some sheen; however, they are just as porous as the edges, requiring special attention during preparation.
You can use the following products to seal MDF boards before painting.
- PVA Glue
Even though PVA glue comes in liquid form, it dries into a robust, solid coat resistant to moisture. To seal MDF with PVA, spray the product or apply it on the surface with a synthetic bristle brush.
Make sure to cover every inch of the surface and keep the layers thin and even. Once the glue dries, sand it with fine-grit sandpaper to smooth out the surface.
The most readily available PVA-based glues are thick; hence they require dilution with water to produce the thin layers for sealing surfaces. Such products will cause more harm than good to your MDF, so it is best to avoid them.
Instead, I recommend going for acid-neutral PVA glues because they are already thin; hence, dilution is unnecessary. Manufacturers usually design these glues for binding books and papers, and they work well with rollers or spray bottles during application.
- Spray-on Lacquer
A good quality lacquer will seal MDF boards and, at the same time, act as a primer for your color. Relying on how you want your finished product to look, you can use either a clear or tinted spray lacquer.
I recommend utilizing lacquers manufacturers designed for finishing outdoor projects because they are more sturdy. Additionally, some traditional lacquers dry into highly glossy coats that make it difficult for paint to grip correctly.
- Sanding Sealer
Sanding sealer is usually extra-thick lacquer and is a favorite among cabinet makers for sealing MDF. It has a dense particle load that builds fast on the MDF surface to shield it from moisture. This product will embed itself between the MDF fibers as it dries, but a lot of it will remain on the surface since it’s thick.
So, after applying the first coat, allow it to dry, then sand off about 80% of the first layer before putting on a second one.
After the next layer dries, smooth it out with fine 320 grit sandpaper before proceeding with your project.
How Do You Get a Smooth Gloss Finish on MDF?
The key to getting a smooth finish on MDF is in the sanding process: sanding the board before coating and sanding between each layer of paint or primer, etc.
Sanding is a tedious job, but if you do it correctly, you can achieve a smooth glossy finish even on the most challenging surfaces to paint, such as MDF. Here’s how:
- Sand In Between Coats.
One of the leading causes of a bumpy paint job on MDF is a rough first coat. The first coat of any finish is also known as the sealing coat, and it will raise the fibers of MDF then lock them in place. So if you forget to smooth out the coat, its roughness will pass through all subsequent layers causing the final finish to have some texture.
The first coat of product you apply on MDF is usually thinner than the follow-ups. The layer’s thinness makes it easy to sand without clogging your sandpaper, so if you forget to sand down the sealing coat, you will need to sand in between each layer that follows to ensure that your product goes on a smooth surface.
If you intend to apply more than two coats of finish, you may find it helpful to smooth out the next-to-last coat before applying the last one. Scuffing will roughen the surface, which will allow the final coat of finish to level better.
- Rub Dried Finish With a Brown Paper Bag.
There’s always some debris and dust in the air that may settle on your drying finish causing it to feel rough. You can remove the textured feeling by rubbing down your dried finish with a folded brown paper bag without the risk of scratching your paint.
Even though this trick effectively removes small debris without leaving scratches in the finish, it cannot smooth your surface if you fail to sand the sealing coat.
- Use Car Paint
Car paints are primarily glossy. They level out evenly on surfaces and dry into a hard, shiny coat, making them ideal for giving MDF a smooth gloss finish.
Glossiness aside, auto paint is more durable than standard paints and resists moisture even better. These features make it ideal for protecting MDF surfaces, especially those outdoors or regularly come into contact with water.
How Do You Paint and Seal MDF?
You can paint and seal MDF using a paintbrush, roller, or sprayer. The tool you choose to use will depend on the size of your project and the amount of time you have to complete it. Let’s look at each technique in detail:
- Using a Roller
Paint rollers are best used on large MDF sheets because they cover a large area quickly. They also tend to produce smoother finishes on MDF compared to paintbrushes. Woodworkers usually use short pile rollers because they pick up little paint allowing for a smoother application.
However, I don’t recommend using them on MDF because they leave a little texture. Instead, go for the smaller 4-inch rollers that are the standard tools for most paint jobs.
- Using a Brush
Paintbrushes are the ideal tools for sealing and painting smaller MDF projects, especially those with intricate details. I recommend using a 2-inch paintbrush on MDF because its small size allows precise control of the painting process.
Since you’ll be using solvent-based products on MDF, I recommend that you purchase natural bristle brushes to help you achieve a smooth finish. Don’t get me wrong, synthetic bristle brushes can also work well with solvent-based products, but you will achieve better results with natural ones.
- Using a Sprayer
Spraying coating products onto MDF is the fastest way to finish them. You get to cover a larger area in a shorter time than the previous two methods, and your results will be smoother.
However, the problem with spray painting is the long time it takes to prepare your work area and the sprayer. It is best to cover everything in the vicinity of your project to avoid overspray problems.
You also need to properly thin out your products and understand how a paint sprayer works to prevent ruining your finish. Because of the application complications with spraying, I recommend leaving this method to professional painters until you master the skill.
Can You Paint MDF With Acrylic Paint?
Yes, you can! Acrylic paint is the best alternative to the commonly used oil-based products because of a few reasons:
First, acrylics use an emulsion to carry their color pigment; hence they dry faster than oil paints. Their fast-drying nature makes them ideal for coating MDF because there is less time for the surface to soak up the color before it hardens.
The other reason is that acrylic paint contains fewer VOCs than oil-based paints; hence, they produce less harmful fumes during application. Furthermore, cleaning brushes and paint trays with acrylic paint is more manageable because you can use water instead of a paint thinner.
You can use water to thin out acrylic paint before putting it on a surface; however, that can cause severe problems in MDF. So I recommend purchasing acrylic products that aren’t water-based and come ready to use without thinning.
How Do I Get a Mirror Finish on MDF?
The best way to achieve a mirror finish on MDF is by wet sanding the clear coat you apply after painting it. This technique is majorly used on car paint jobs or guitars to give them that classic shiny look that we all love.
Unlike dry sanding, wet sanding does not shape the surface; instead, it removes the deep scratches left on a finish after dry sanding. When you do it correctly, the finish will level out slowly, and the scratches will become smaller until the surface looks like a mirror.
Many people worry about wet sanding MDF because they fear that the board will soak the water and sustain irreparable damages.
However, there’s a way to avoid problems, and that is by saturating the sandpaper overnight and only wet sanding the final coating product after the whole board’s protected. (Don’t wet-sand an uncoated MDF board!)
When you soak the sandpaper overnight, it soaks up enough moisture to keep it clean as you wet sand so you won’t have to keep wetting it. Even if you wet the paper during the process, you’ll need less water, reducing the chances of ruining your MDF.
Since the purpose of wet sanding is to smooth out scratches left after dry sanding, it is best to start with sandpaper with a higher grit than the last one you used on your surface. For instance, if you dry-sand your clear coat with 320 grit sandpaper, start the wet sanding with a 400 grit paper.
As you continue the process, change your sandpaper for newer ones with even higher grits to ensure that the scratches you make are too minor to see with the naked eye. You can wet sand with up to 1500 grit if you want to give your MDF that flawless mirror-like finish.
Here’s How to Get a Glossy Finish On MDF:
Conclusion
Medium Density Fiberboard or MDF is a cheap and practical alternative to wood. You can use it for small projects like furniture or make skirting boards for your home. The problem with this building material is that it doesn’t have any perceivable wood grain patterns. It may be brown like wood, but it lacks the allure of using natural wood.
The best way to refresh the look of MDF is by painting. However, since it is a highly porous surface, it will soak up the moisture in paint, leaving you with a peeling paint job. You may wonder…
What Steps Should I Follow to Properly Paint MDF?
The crucial first step to painting MDF is to seal the whole board to prevent it from absorbing moisture from the products you put on it.
Start by filling the edges with wood filler, then apply a sanding sealer to seal the faces of the board. Next, sand down the sealer, then use a solvent-based primer for extra moisture protection and to give your paint a good surface to grip. Once the primer dries, sand it down with fine-grit sandpaper, then apply paint as usual.
It is best to use solvent-based products throughout the process as water-based products will make MDF swell or warp. However, you can also use acrylic paint to color MDF but make sure that you purchase a brand that is already thinned so that you won’t have to mix it with water.
