If you want to know how to prime MDF board for painting, you’re in the right place.
Priming is the most important step for preparing any surface for painting, and MDF is no different. Priming MDF is the step that will determine whether or not the paint finish will last a long time.
You must use the correct products and apply them correctly to guarantee a flawless finish. So I wrote this article to show you How To Prime MDF Board For Painting.
Start by sealing the MDF board’s edges using wood filler, edging tape, or PVA glue. Next, sand the edges to smooth down the filler and lightly sand the board’s flat surfaces.
Use a hand vacuum to suck up most of the sanding dust, then wipe the board with a cloth to remove any remaining dirt. Finally, apply two coats of a solvent-based primer and allow it to dry properly before painting.
I have summarized these basic steps to give you a quick run-through of how to prime MDF boards correctly.
But, in this article, I will explain each step in depth, telling you which products to use and why you should use them. Let’s begin.
What Is Primer?
A primer is a product you apply to surfaces before applying paint. It is a preparatory coating designed to minimize the natural flaws of a material that would make painting difficult.
Take wood, for example. It is highly porous and absorbs any liquid on its surface – paint is no different. But when you apply a primer, the product seals the pores, thus preventing the material from absorbing paint.
A primer’s primary function on metal surfaces is to negate reactions between the paint and the surface. As a result, there’s no risk of the metal corroding and weakening over time.
Besides the abovementioned reasons, primers generally improve the bond between the surface and the paint. As a result, the finish won’t peel off or chip prematurely. In addition, primers hide stains that would otherwise show through a paint finish.
Types of Primers
There are several surface primers, but the primary ones are Oil-based, latex, and shellac. They perform similar functions; however, their different chemical compositions make each better suited for some projects than others. Let me explain.
- Oil-based primers are the most versatile variety, as you can paint over them with either oil- or water-based paint. They have excellent stain-blocking capabilities, making them the ideal choice if you have a surface with flaws that need hiding.
Unfortunately, oil-based primers take too long to dry, causing projects to run longer. Moreover, they contain Volatile Organic Compounds (VOCs) and produce a terrible odor; hence they are not entirely environmentally friendly.
Oil-based primers also require harsh chemicals like mineral spirits and paint thinners for cleanup because water can’t dissolve oil.
Furthermore, they are less flexible than other primers and tend to get more rigid as time passes. As a result, they become brittle and are prone to cracking.
- Latex primers are water-based and don’t contain VOCs or produce a foul odor. The water base also makes these products easy to clean using only water and a slight rubbing. Furthermore, they dry quickly; thus, project completion is faster.
On the downside, latex primers do not hold up well in harsh conditions; hence, they are best used on indoor surfaces. You may use them on outdoor surfaces, but you must ensure that the item you’re painting is adequately shielded from the elements.
Latex primers also have poor stain-blocking capabilities; hence, they don’t produce flawless results on highly stained surfaces. Don’t get me wrong; the primer will hide stains, but not as effective as the other primers on this list.
- Shellac Primers are the best stain blockers because they hide everything, including odors. They are also highly adhesive and versatile, just like the oil-based variety. For this reason, any project started with a shellac primer will last longer than average.
Unfortunately, shellac primers have a foul odor that can linger many hours after application. In addition, they don’t hold up well outdoors; therefore, it is best to restrict their use to indoor or appropriately shaded surfaces.
Pros of Primer
- One of the functions of a primer is to create a neutral-colored surface for painting. The neutral color won’t interfere with the paint’s actual color, bringing out the natural color of the paint.
- Creating a neutral-colored surface allows you to achieve full coverage with only a few coats. If you paint without priming, the surface’s color will show through the first few coats, forcing you to apply more layers for full coverage.
- Primer improves the bond between paint and surfaces, and as a result, the finish will last longer than if you painted without priming first.
Cons of Primer
- The only disadvantage of primer is that it prolongs the painting process. It would’ve been quicker if it were possible to slap paint on a surface immediately. However, in addition to the actual painting duration, you must wait for the primer to cure before applying the color.
What Is a Paint?
Paint is a colored liquid you apply on surfaces to protect them from quick degradation. It dries into a tough coat that can withstand harsh conditions, protecting the surface by default.
In addition, paint is perfect for decorating old or plain-looking surfaces because it comes in several color assortments and finish types. The color variations allow you to pick the best paint that fits your style.
There are several types of paint on the market, each with a unique formulation that makes them suitable for some projects more than others. You need to understand the unique advantages of each type of paint to make selection easier.
Before looking at the different types of paint, let me tell you about the components that make up paint in general. Once you understand the function of each component, you will have better insight into the different paint types as I discuss them.
Paint has three main ingredients – pigments, binders (resin), and a solvent.
- The pigment gives the paint its unique color. It also determines the thickness of the paint and its ability to hide flaws on surfaces.
- The binder holds the pigment particles together, ensuring the paint film is hard enough to resist destructive elements. It also affects how well the paint adheres to surfaces.
- The solvent is the “carrier” of the pigment and the binder. It allows the smooth transfer of the other ingredients from the container to the surface. However, the liquid carrier evaporates as the paint dries, leaving the solid ingredients on the surface. It does not affect the decorative or protective properties of the product.
Some paint manufacturers add special additives to the main ingredients to give their products additional superior characteristics.
You will find paints with additives that improve adhesion or help the product resist mold, mildew, and damage from UV rays. The additives usually make up a tiny percentage of the paint, but they can drive up paint costs by up to 5%.
Types of Paint
- Water-Based Paint
Water-based paints, aka latex paints, contain a pigment and binder with water as the solvent. Since they don’t use oils or harsh chemicals, these paint types have extremely low VOC levels making them ideal for painting indoor surfaces.
Furthermore, they retain a “soft finish” after they cure, so using them on items that don’t get much use is best.
- Oil-based paint
The formula of Oil-based paint includes pigment and a linseed oil binder suspended in mineral spirits – the carrier could also be any other thinning solvent made from petroleum.
It is the most durable paint type on this list because it dries into a more rigid film than the rest.
Nevertheless, the durability of oil-based paint comes at a high cost. First, these paints are more expensive and take too long to dry between coats(up to 24 hours). Moreover, they have high VOC levels and release toxic fumes up to one week after applying the final coat.
This paint type is best used on exterior surfaces because they are more exposed to the elements. Furthermore, using this type of paint outside will save you from dealing with lingering paint fumes.
- Acrylic paint
Paint manufacturers formulate acrylic paint by suspending color pigment and acrylic resin in an acrylic polymer solution. It is the most versatile paint type, ideal for many surfaces, including wood, leather, and canvas.
Acrylic paint is easy to apply because of its self-leveling properties. As you use it, the product flows evenly on the surface, so you won’t have any problems smoothing out the paint film.
In addition, it takes a short time to dry between coats, allowing you to finish projects more quickly.
On the protective side, the dry film of acrylic paint has more elasticity, allowing it to move with the substrate as it expands and contracts. Consequently, it is more resistant to chipping and cracking.
Pros of Paint
- Paint comes in several colors and sheens, giving room for choices.
- The paint dries into a hard coat that protects the surface from dents and water damage.
- Paint is inexpensive, thus making painting the most affordable way of completely changing the appearance of a surface.
Cons of Paint
- Paint is easy to apply but quite challenging to remove. As a result, it is not the best option if you want temporary customization of a surface.
- Most types of paint require harsh chemicals and a lot of time to clean up.
- Painting requires skill and proper preparation, and patience. If you rush the job or apply the paint using improper techniques, your projects won’t turn out flawless.
What Is MDF?
Medium Density fiberboard (MDF) is an engineered wood made by gluing wood residuals together using a synthetic adhesive. The resulting material is stable and strong and is often used as a wood alternative in some projects.
The residuals used to make the boards can be from softwood or hardwood species. Whether you combine or use the species individually doesn’t matter as long as their relative densities are close.
Characteristics of MDF
MDF boards are usually tan or dark brown and are sold in either 1/2-inch or 3/4-inch thick sheets. Unlike natural wood, MDF boards have a smooth surface without visible knots or rings.
Their uniform appearance remains consistent even if you cut the board at different angles. This general uniform appearance is one of the things that makes MDF so popular.
The other characteristic that makes builders favor MDF is how easy it is to attach the boards. You can join them quickly using adhesives like epoxies, PVA glue, or plastic resins.
If you want physical fasteners, you’ll never go wrong with composite wood screws. The best ones available today are pan-head machine screws and T-nuts, but you can also use any standard screws, provided they have a coarse thread pitch.
On the downside, MDF boards are porous – even more than natural wood. For this reason, they are prone to water damage, which can make painting a little challenging.
In addition, MDF boards tend to be weaker close to the edges; hence you must take extra care not to ruin the boards while cutting or attaching them.
Types of MDF Boards
The three primary types of MDF boards are lightweight, standard-grade, and High-Density.
- Lightweight MDF boards are the lightest and have loosely packed fibers. Additionally, manufacturers use very little adhesive to glue the wood residuals making the boards appear soft and brittle.
- Standard Grade MDF boards contain just the right amount of fibers and adhesive. They present all the standard features you look for in MDF – excellent strength, durability, and sufficient density.
- High-Density MDF boards have more wood fibers tightly packed together. They are the strongest, most durable, and heaviest type of MDF.
You can also find specialized MDF boards in the grades mentioned above. These boards have a few additional perks that make them stronger and better at resisting moisture and fire damage. The two main types of specialized MDF are fire-retardant and moisture-resistant MDF.
- Fire Retardant MDF boards are infused with chemicals that make their wood fibers less flammable. They don’t catch fire easily, but the fire will not spread quickly if they do.
This MDF type is best used in areas with regular open flames, such as kitchens. And you can identify them by a red or blue stamp at the board’s edge.
- On the other hand, moisture-resistant MDF boards are equipped to resist moisture damage, which is the biggest issue with MDF boards.
Manufacturers use paraffin wax and a moisture-repellant resin to make them waterproof, allowing you to use them in places where the surface has a high chance of getting wet, such as kitchens and bathrooms.
On the downside, moisture-resistant MDF is not fully waterproof and will be damaged if submerged.
Uses of MDF Boards
MDF boards are commonly used to make low-cost furniture, specifically indoor furniture that you use minimally. They are also suitable for trimming work and building shelves and cabinets due to their lack of knots and excellent workability.
Their light weight also makes them ideal for building items that must be constantly moved, such as tradeshow booths, mobile homes, event setups, and theater set constructions.
Pros of MDF
- MDF is cheaper than natural wood.
- The appearance of MDF boards is consistent throughout the board; therefore, all cut edges appear smooth, and you don’t have to worry about voids or splinters.
- MDF has excellent workability – it is easy to cut and attach using adhesives or composite wood fasteners.
- The surface of MDF is easy to paint.
Cons of MDF
- MDF soaks up water and other liquids quickly and eventually swells out of shape. Therefore, you must always seal its surface to keep it in good shape.
- Even though it is easy to attach MDF boards, they do not hold screws very well.
- MDF boards produce a lot of dust when you cut or sand them.
- MDF boards tend to bend or sag when you put a lot of weight on them.
What Kind of Primer Should I Use On MDF?
Oil-based primers are the best products for preparing MDF boards because they do not contain water in their formula.
In addition, they won’t react with the adhesives used to glue the wood particles used to make the boards. Therefore, you can rest assured that your board won’t get damaged after application.
I do not recommend using latex primers because they penetrate the MDF board and cause it to swell. Also, avoid using multipurpose primers because most of them will cause the MDF to fall apart.
If you don’t have an oil primer, there are other alternative products that you can use and still get a perfect paint finish on MDF. These are:
Acid-neutral PVA Glue
An acid-neutral PVA glue is usually designed for binding books and paper. Still, it makes an excellent primer substitute for MDF.
It differs slightly from conventional PVA glues we use as wood adhesives. Its consistency is already thin enough to make it easy to spread with a brush, sprayer, or roller.
Do not use the regular PVA glues because they are thick and therefore need dilution to produce thin sealing layers. The dilution requires water, which will cause the material to swell and get damaged.
Spray-on Lacquer
Clear and tinted lacquers are often used as sealers for MDF boards that are meant to remain unpainted. However, the lacquer layer can also act as a perfect primer for the paint to follow.
It is best to select a lacquer designed for finishing outdoor surfaces because most standard lacquers dry into a glossy film that paint won’t adhere to easily.
How to Prime MDF Board for Painting
Priming MDF before painting is essential, but you don’t just go in and slap the primer onto the surface. If you do that, the finish results will be as bad as if you painted over the board without priming. So let me show you how to prime the MDF board correctly.
You Will Need
- Oil-based primer
- Paint brushes, roller, or sprayer
- Tack cloths
- A hand vacuum
- A drop cloth
- 220-grit silicone-carbide sandpaper
- Protective gear – coveralls, gloves, goggles, and a mask.
- Edge sealer – wood filler, PVA glue, or edging tape.
Step One: General Preparation
- Wear protective gear like goggles, a dust mask, and coveralls to avoid direct contact with fumes and chemicals in the primer. The dust mask will also protect you from inhaling dust from the MDF and fumes from the primer.
- Set up a temporary outdoor workstation or open doors and windows for ventilation if your boards are fixed indoors.
- Lay down a drop cloth to protect your floors from sanding dust and liquid spills.
Step Two: Seal the Edges of the MDF
The edges of an MDF board are more porous and will suck up more product than the surface. Therefore, seal them before priming to make them smooth and consistent like the surface.
The three products you can use to seal the edges of MDF are wood filler, edging tape, and PVA glue. Let me explain how to use each of them.
Sealing the Edges With Wood Filler
Wood filler/putty is commonly used to fill cracks and holes on natural wood surfaces. It is loaded with the necessary binders and resins that will make the edges of MDF uniform with the surface.
- Use your fingers or a putty knife to apply the filler and then let it dry for the duration recommended on the product’s user instructions. The application, at this point, doesn’t have to be flawless – any mistakes you make will be rectified by sanding.
Sealing the Edges With PVA Glue
PVA wood glue is a standard product in every woodworking shop, and it will save you from buying sealing products for MDF.
- Apply it over the edges using a synthetic paintbrush or a glue spreader for the best results. You can also spray it over the edge if you have wood glue in a spray bottle.
Sealing the Edges With Edging Tape
Edging tape, aka edge banding, is a thin strip of adhesive veneer that you put over composite wood edges to make it look like the surface. It comes pre-glued on one side and is available in various sizes to fit all kinds of MDF.
- Cut the edging tape into strips a few inches larger than the length and width of your MDF edges.
- Place the cut strip over the edge, then apply heat to activate the glue. Use a regular household iron on a medium heat setting and move it slowly over the strip. Ensure you apply gentle and even pressure to prevent the tape from lifting off in some parts.
- Afterward, trim off the excess edging tape hanging on each end.
Step Three: Sand the Entire MDF Board
- After the edge sealers dry properly, use the 220-grit silicone-carbide sandpaper to smooth the edges. The goal is to knock down raised spots and make the edges consistent with the rest of the board. Therefore, use minimal pressure to avoid sanding down the edges excessively.
- Once you’re done with the edges, sand the faces of the boards to help the primer stick better. This is especially important if you have prefinished MDF because it will rough up the sleek factory finish.
- Finally, use a hand vacuum to suck up the sanding dust and then wipe with a clean, dry tack cloth to remove dust residues. Avoid using a damp tack cloth for this step because you risk damaging the board before painting.
Step Four: Prime the MDF
- Pour a little primer into a separate container, then dip your paintbrush to pick up some product.
- Wipe excess product onto the inner lip of the container and then apply the primer in long strokes over the MDF. Ensure you overlap each stroke to avoid leaving some bare spots on the surface.
- Pay close attention to the edges and corners of the board, ensuring you cover them completely.
- Let the first primer coat dry as instructed on the product, and then sand it lightly to get it ready for a second coat. Wipe off the sanding dust before applying the next primer layer.
- Apply a second primer coat using the same techniques as the first for the best results.
Note: Two coats of primer are standard, but you can apply more if mentioned in your product’s user instructions. Ensure that you sand between coats to make them adhere to each other perfectly.
How to Prime MDF:
How to Paint MDF Board
Once you’ve primed the MDF, apply an oil-based paint because it is durable and offers superior moisture protection than most paints.
You can also use latex paint at this point because the oil-based primer used to prepare the surface will prevent moisture in the paint from damaging the board.
- Load a paintbrush with a bit of paint, then apply it to the outer edges of the MDF. Ensure that you maintain a wet edge as you work to prevent lap marks from showing in the finish.
- Next, use a paint roller to add color to the middle of the board. Start rolling with light pressure, then gently increase it as you continue working.
- It is best to start with light pressure because, at that point, the roller sleeve has a lot of paint on its surface. Therefore, it is not hard to transfer the paint to the surface. However, the paint on the roller’s surface subsides as you keep working, so you must increase pressure to release more paint.
- Let the first coat dry, then apply another coat following the same procedure. Afterward, allow the paint to cure before touching or using the painted MDF item.
How to Paint MDF Board:
Do You Need to Seal MDF After Painting?
Yes, you do. Sealing MDF boards after you paint them is especially important for items you use frequently or MDF trimmings in high-traffic areas. Here’s why.
The sealants used after painting are harder to wear than paint; therefore, they can resist dings and scratches better. In addition, the clear coat locks in the paint color, preventing it from fading over time. As a result, the paint finish remains in pristine condition for longer than average.
Another reason for sealing MDF is to make the board even more waterproof. Even though the paint protects it from moisture damage, adding a sealer will cement that protection and make it last longer.
The clear coat also prevents the paint from getting water rings and makes the painted MDF boards easy to clean without water damage.
I recommend using polyurethane to seal MDF after painting because it forms the sturdiest film, meaning better overall protection. You can use water- or oil-based polyurethane, depending on how you want the finish to look. Let me explain.
Oil-based polyurethane is highly durable and will protect your MDF finish for a long time.
However, it turns slightly yellow with age, and the color change always affects the finish appearance. So, if you want superior protection and don’t mind a slight color change, use the oil polyurethanes.
On the other hand, water-based polyurethanes are durable but not as durable as oil-based varieties. But, on the bright side, they do not change color over time; therefore, you don’t have to worry about your MDF finish changing as well.
That said, let me now show you how to seal MDF after painting.
- After the last paint coat dries, use fine-grit sandpaper to lightly scuff the surface before applying the clear coat. Sanding at this point helps remove any dirt stuck on the finish while the paint is drying. It also makes the sleek painted surface a little rough to allow the clear coat to adhere properly.
- Afterward, wipe the surface with a damp tack cloth to remove the sanding dust and allow the surface to dry for a few hours.
- Apply at least two thin coats of the clear coat using the same techniques you used when applying paint and primer. Ensure you sand between coats to make them stick firmly together.
- After the final coat, allow the surface to cure before you move or use the painted item. It could take up to one week for the finish to cure correctly, so it is best to be patient.
Why Is MDF Rough After Painting?
If your MDF board is rough after painting, the likely reason is that you did not apply primer before painting. Even if you use oil-based paint, the first coat will raise the wood fibers, making the finish appear “fuzzy” rather than smooth.
The MDF could also be rough if you used a water-based or multipurpose primer instead of an oil-based one. When you apply a water-based primer on MDF, the surface soaks up the moisture in the primer and starts to swell.
As a result, the adhesive holding the wood fibers weakens, causing the wood fibers to flare out – much like raised wood grain in natural wood.
If you want a guaranteed smooth paint finish on MDF, begin by priming the board with an oil-based primer to seal the surface before painting.
Is MDF Easier to Paint Than Plywood?
Painting MDF and plywood requires the same amount of preparation work. Therefore, none is easier to paint than the other. Let me explain.
The first step before painting MDF is sealing the edges to make the finish smooth and consistent throughout the board. The same applies to plywood because its edges often have spaces between the wood veneer sheets.
Even the products required to seal the edges are similar for both kinds of wood. After sealing, the priming and painting process is similar for both kinds of wood.
Nevertheless, the painting process for both MDF and plywood can seem quite difficult if you lack the necessary painting skills. Using the wrong products can also make the task much harder, and you could damage many boards until you make some changes
Conclusion
MDF boards are becoming a popular wood alternative because they are more affordable than natural wood. They are also free from knots and imperfections commonly seen on natural wood.
For these reasons, woodworkers use MDF to make furniture, wood trimming, cabinets, shelves, etc.
The only downside of MDF is that its lack of visible grain makes it look a little plain, and therefore you must paint it to make it more beautiful.
However, you must prime the boards properly before applying the paint to get a flawless finish and prevent them from getting water damage. So I wrote this article to show you…
How to Prime MDF Board for Painting.
We’ve seen that sealing the edges of MDF is crucial before priming to ensure a consistent finish throughout the board. After sealing, apply an oil-based primer on the surface to prevent the MDF from absorbing moisture from the paint.
If you don’t have an oil-based primer, you can still get flawless results if you seal the surface using acid-neutral PVA glue or a spray-on lacquer finish.
After priming, the painting process is easy if you use the necessary techniques. However, you must seal the painted MDF board with water- or oil-based polyurethane to lock in the color and guarantee extra moisture protection for the board.
Thank you for reading this far, and I hope the instructions for priming MDF are clear. If you need clarification, please reach me in the comments below.
