Sealing MDF – How to Seal MDF Before Painting (Board & Workbench)

Do you know how to seal MDF before painting? Painting Medium Density Fiberboard is one way to protect it from absorbing moisture and getting damaged.

However, you must seal MDF if you want to paint it because the material is highly porous and could soak up an incredible amount of the product and swell if in direct contact with the elements.

So, sealing MDF boards before painting is the most crucial part of working with this material.

How Seal MDF Boards Before Painting

We don’t recommend painting MDF without sealing because MDF absorbs the moisture in the paint. Sealing MDF begins with sanding the MDF, sealing its edges using MDF edging tape or PVA glue, and sealing the surface using enamel primer or PVA glue.

How to Seal MDF from Moisture

There’re various ways to seal MDF and protect it from moisture and humidity threats. Here is the process to follow and the materials you will need for this task.

The materials you will need 

• A face mask
• Safety goggles 
• Long-sleeved clothing or an overall
• Sandpaper or sanding pad 
• Gloves
• Sealer 
• Synthetic-bristled paintbrushes
• Paint roller 
• Putty knife 
• Dropcloth or plastic sheeting

Steps to Follow When Sealing MDF Boards 

How meticulously you seal MDF edges will determine their service life. You want to completely waterproof the workbench top to avoid any room for moisture and water damage. 

Here are the steps to follow when sealing MDF before painting. 

Step 1: Prepare yourself.

You will be handling products with various chemical compositions. Some of these chemicals may be harmful to your skin. 

While a good majority of the sealing products to use when sealing MDF are safe to touch or inhale their scent, it is always better to err on the side of caution. So, we recommend taking all the necessary safety precautions before you begin.

Ideally, work from a well-ventilated area. This location can be your garage, workshop, or some sheltered place outside your house. Also, wear a pair of gloves and long-sleeved clothing or overall. 

Whichever place you choose for the exercise, ensure you cover the floor and any nearby object with a drop cloth or plastic sheeting. The cover protects these objects and the floor from sanding dust, sealing agents, and paint spills.  

You may also need to wear eye protection and a safety mask, depending on the sealers you will use.

Read also: Can you put Thompson water seal over stained wood?

Step 2: Scuff sand the workbench top 

You need a wooden workbench that is neither too rough nor too smooth to get the best sealing results before painting. Sanding ensures you achieve that kind of surface. 

Consider using medium grit sandpaper for the best results. You could use 220-grit sandpaper or sanding block for more control. 

For this part, consider wearing eye protection and a safety mask. You don’t want to have the wood dust getting inside your eyes or lungs.

You can sand in circular motions, keeping the pressure light and evenly distributed across the entire surface and on the edges—there’s no need to follow any grain with the inexpensive wood product. 

Step 3: Seal the edges 

Always start with the edges when working with a medium-density fiberboard. The edges are generally more porous and rougher than either side. As a result, they can take in an incredible amount of water or paint, causing irreparable damage if unsealed. 

You will need to use a sealing agent to solidify and form an impenetrable coat on these edges before working on the two sides.

There’re various products and methods to choose from. Let us look at five of the available sealing options below.  

Method 1: MDF edging tape 

The edging tape, also called edge banding, is a thin strip of adhesive veneer that comes pre-glued on one side. It is available in various sizes and types across different price ranges. 

All you have to do when sealing the edges of your MDF project with this material is cut the sheets into strips matching the width and length of your MDF edges. Ensure you leave a little bit of it going over the edge of the composite board. 

Place the matching MDF edging tape strip over the edge and apply heat. The easiest way to heat it and stimulate adhesion is to iron it onto the MDF. Ensure the household iron is on a medium heat setting and move it slowly over the sheet, applying gentle, even pressure.

After ironing, smooth it with a block of wood to ensure it adheres nicely and evenly. 

Once done, carefully trim off the edges to eliminate the excess sheeting and overhang on each end. The sealed MDF panel can be sanded when dry. 

Method 2: PVA glue

It is straightforward to seal the edges with PVA glue. You can apply the product with a synthetic brush or glue spreader. You can also spray it over the edge you want to seal with a sprayer. The latter method is best if you have the wood glue in a spray bottle.

After applying, wait for the coat to dry, then lightly sand it down with medium-grit sandpaper. Don’t apply too much pressure when sanding; the idea is only to scuff it up a bit. So, watch out not to remove the layer you have applied with the sander. 

Method 3: Wood filler 

One of the best ways to seal the edges or flat surfaces of your MDF board is using thinned wood filler or putty. Use a putty knife to apply an even coat of filler on the edges to achieve a thin layer over the surface.

Let the wood filler thoroughly for the amount of time the manufacturer has recommended, then sand it down to smooth the surface. 

Consider using a wood filler that is the same color as your MDF for the best results. You can also decide to make your own wood filler.

Method 4: Oil-based filling primer

Sealing the edges with oil-based filling primers is another easy method. You can apply the product the same way as PVA glue—apply it using a synthetic fiber brush, or spray it on the edges with a sprayer.

Leave the oil-based filling primer on the board to dry completely, then sand it down. You want to watch out not to sand the entire layer off, as that would beat the purpose of applying it in the first place. 

Simply scuff it up slightly to ready it for painting. 

Method 5: Using drywall compound and primer

The final method in our list involves using a combination of drywall compound and lacquer primer. As you may notice, this is a two-step process, so it is slightly longer than the first four.

Start by rubbing the drywall compound evenly on the edges of your MDF workbench top and let it dry. Then, while applying the compound, wipe off the excess as you go to achieve an even coat. 

The amount of drying time may vary with various products, so ensure you follow the manufacturer’s recommendation.

Once the surface has dried, scuff sand it just as you would with the previous methods discussed, then apply a lacquer primer. You use a brush or roller to apply the primer or stick to what the manufacturer recommends. 

You may need to give the edge another extra sanding after applying the primer layer for the best results. Never use a water-based paint primer or a latex primer.

Step 4: Seal the surface

Now that you have finished sealing the edges of MDF using one of the methods discussed, it is time to seal both sides of the workbench top for a smooth finish. 

While MDF is available in varying sheens, it is still significantly porous on the surface and could absorb significant amounts of water and moisture. This porosity is the reason you need to seal it properly before painting. 

Also, applying MDF paint directly to the board could cause adhesion problems due to the slick sheen of most MDF pieces. So, use one of these methods to ready the board for painting. 

Method 1: Using PVA Glue

PVA glue is available in liquid form even though it dries to form a robust and solid coat. 

To seal the surfaces with this glue, spray or apply it with a synthetic bristled paintbrush. Ensure you keep the layers thin and even, and cover every inch of the surface.

A good majority of PVA-based glues need dilution to produce the required thin sealing layers. Since these are diluted with water, the solvent may cause the MDF material to swell and get damaged. 

Therefore, consider going for acid-neutral PVA glues that are already thin. These are usually designed for binding books and papers and work well with a spreader, roller, or spray bottle during application.

Method 2: Using a Spray-on lacquer 

A clear-colored or tinted spray lacquer is the best workbench finish you can use The lacquer will seal the MDF and act as a primer for the paint to follow. 

We recommend lacquers designed for finishing outdoor projects because some standard lacquers dry to form highly glossy coats that most paints won’t adhere to.

In any case, always follow the application instructions when working with lacquer primers on MDF to get the best results. 

Read also: Can Thompson’s water seal be sprayed?

Method 3: Using an enamel primer 

Consider applying thin coats of your chosen enamel primer to cover the MDF all around. Enamel primers are the most effective products for priming MDF surfaces, especially when you intend to paint over them.

Ensure the primer color you have chosen complements the color of the paint you intend to apply over it. 

Why do you Need to Seal MDF Boards? 

You need to seal medium-density fiberboards for two main reasons. 

To prevent water and moisture penetration

MDF is a composite material made by gluing together wood chips under specific temperature and pressure conditions. Just like natural wood, the composite material retains a significant level of porosity.

However, unlike natural wood, MDF is more open on the edges.

The material can absorb lots of water and swell, become warped and lose its structural integrity for good. This way, water or moisture can cause irreparable damage to medium-density fiberboards. 

To prolong its service life

MDF is a durable product. But moisture damage can cut its life short. Sealing it is one way to guarantee it will retain its structural integrity for longer and remain sound for as long as it should. 

Essential Tips for Sealing MDF Boards 

You may have noticed that sealing MDF is a relatively straightforward process. However, missing a step or two can break the entire project. Here are some tips to help you avoid the common pitfalls along the way. 

• Don’t use a latex or water-based paint primer on MDF’s surface. The composite material would soak up the water and become warped. 
• Avoid any water-based glues when sealing MDF. The water can damage the composite material. Consider using acid-neutral options instead. 
• Don’t use a natural-bristled brush when sealing MDF. Instead, use a roller, high-quality synthetic paintbrush, or spray bottle.
• Apply thin coats of sealer to facilitate quick drying and a more even surface. 

Read also: Do you need to seal cedar wood?

FAQs

Can you waterproof MDF?

Yes, you can waterproof MDF boards through painting. Once you have sealed your boards, apply oil-based paint to coat the composite material and make it resistant to water and moisture.  

What is a good sealer for MDF?

De-waxed shellac is an ideal sealer for both the edges of MDF and the flat surfaces. In addition, the shellac is relatively a lot cheaper, making it an excellent option for most professional and DIY painters and carpenters. 

Can you coat MDF to make it waterproof?

Absolutely. You can add high-quality sealant, stain, varnish, or moisture-resistant paint to MDF and make it waterproof. With the coating, the MDF material can withstand threats of humidity and moisture common in outdoor environments. While coating your MDF, ensure you don’t use waterborne polyurethane as it is unlikely to bond well with the MDF surface. Chek out can mdf be stained if you thinking of staining your MDF

Read also: Difference between polyurethane and sanding sealer.

Do I need to seal the MDF before painting?

Yes. Sealing MDF before coating it with paint is essential as it ensures the board doesn’t soak up the solvent in the paint and get warped and swollen. Since MDF is highly porous, it can absorb the paint, leading to unsightly blotchiness and discoloration.

How to seal Particle Board

To seal particle board, use a paintbrush; you can seal particle board by applying a coat of waterproof or clear acrylic sealant over all the edges of the board and other areas more exposed to moisture.

Related reads:

How to Seal Painted Wood for Outdoor Use

Shou Sugi ban sealer.

How to Seal MDF Boards Before Painting Summary

So, that’s it! The steps for how to seal MDF boards before painting. Now you have the skills to create seamless and beautiful pieces of furniture or art with the best results.

And, with some practice and dedication, these tips can help you create something truly unique that will last just as long as your passion projects. Remember, carefully sand down the surface of all your boards, fighting against the grain.

Then thoroughly prime them all with a brush or sprayer on both sides of every board before allowing them to dry completely before assembling together at standard workbench height.

With this technique, you can say goodbye to sloppy projects and hello to beautiful works of art that you are proud of.