Now it's time to get to sanding! Water damaged MDF is evident by its bubbles, so sanding it down so that the material is even and smooth is critical. You can choose to do this step either by hand or with an electric sander. Selecting a medium-fine grit, around 100 or 120, is a safe bet.
To repair the water and steam damage, first, we have to cut away the puffed up damaged wood fibers. We then sand it smooth. Next, we use a solvent based primer, I like BIN shellac primer for this because it penetrates, it seals, and it dries fast. The area is sanded then primed one more time.
Although the goal is to remove the raised grain from the damaged area, it's important to sand the entire surface to maintain consistency. The grain is raised very slightly in the water-damaged area, so a little sanding with 400 grit paper is necessary (Photo 3). This step should take about one minute.
Consequently, repairing cracked MDF is usually a simple matter. Although any type of wood filler is suitable for cosmetic repairs, you should use one with structural strength if the repair has to hold screws or nails.
You can also create waterproof MDF by adding a high quality wood sealant, varnish or stain or moisture-resistant paint so that your project can withstand threats of moisture and humidity. Do not use waterborne polyurethane, as it may not bind readily to the MDF's surface.
Water damaged wood can be difficult to repair. Even though most wood finishes protect the surface, it is still possible for the wood to become damaged by water. If you see white spots, stains, blushing or other surface discoloration, then the likelihood is that the wood is being attacked by water.
To fix watermarks or stains on wood, you should have applied marine-grade polyurethane to the wooden furniture in the first place. But, you can still remove watermarks through some other alternative methods.
To repair a veneer blister, carefully slit it open with a razor knife. Then use a glue syringe or a toothpick to apply yellow carpenter's glue beneath the veneer. Press down lightly on the blister to spread the glue. Cover the repair with wax paper and a flat wood block, then clamp the blister flat.
MDF in its undefiled manufactured state is stable and consistent. When it gets wet, it swells and distorts. Swells can be sanded down if the MDF hasn't crumbled or separated to any extent.
Standard MDF can get wet and get damaged by water and high moisture in the air just like most wood products. It does not hold up to water very well. Because of how standard MDF is made, it sucks moisture like a sponge, and will swell, distort, and almost become useless if not treated or sealed.
Combine equal parts vinegar and olive oil in a shallow bowl, stirring with a spoon. Dip a soft cloth into the mixture and apply it to the damaged area, following the direction of the wood grain. Rub the oily solution in with a dry, soft cloth, generally rubbing with the grain, to buff and shine the wood.
In a small bowl, mix equal parts vinegar and olive oil. Apply the mixture to the water stain using a cloth. Wipe in the direction of the wood grain until the stain is gone. The vinegar will help remove the stain while the olive oil acts as a furniture polish.
A quick and simple fix for many cabinets with water stains is an application of paste wax such as Brimax paste wax, a blend of beeswax, carnauba and petroleum, or Harrell's Jecowax Beeswax Blend. Using a clean cloth, apply the paste wax as directed and then wipe the cabinet surface to clean and shine.
Applying additional moisture and heat to the opposite side of the warp can cause the wood to warp back into its original flat position, effectively “unwrapping” the piece. Minor warping can usually be corrected with heat and moisture only, but for more severe warping, you may also need to apply pressure to the wood.
Prime the surface of the furniture with a bonding primer. Apply the primer with a paintbrush in all corners and hard-to-reach areas. Follow with a smooth foam roller to paint the larger surfaces. Allow the primer to dry.
Seal MDF Edges Which Are the Most Absorbent
You can use an acrylic paint sealer or drywall sealer, or you can use glue or oil based primers which will help prevent the edges from swelling. Use whichever primer will dry fastest in your particular humidity.
To answer the question of whether you can paint MDF, the answer is simple, yes you can paint MDF. As with any painting project, it must be properly prepared and painted with the most suitable paint for its particular composition.
Making MDF water-resistant
What you need is a high quality wood varnish, sealant or stain – Ronseal Quick Drying Woodstain is a great option that is highly water repellent and able to withstand the threat of moisture and humidity.
If you like the natural look of MDF and want to add some protection you can use a clear varnish - choose matt or gloss - to keep your MDF looking like new. An oil-based varnish is the best choice for this. You apply in much the same way as primer/sealer/paint, with a brush or roller.
MDF can be sealed with polyurethane. MDF, which stands for medium fiberboard, is used for many household applications such as shelves and speaker boxes. It is is easier to work with than regular plywood or particle board.
Start with a courser grit sand paper, and sand out all of the scratches and damaged spots. Move the sander in the direction of the wood grain as much as possible. Try to get off all of the old finish as well, so your new finish will go on smoothly. Be patient and do this part well.