Polyurethane varnish is a protective coating that is applied to wood to protect it from deterioration and other damage. Regardless of whether it is oil or water based, you can choose it with a glossy or matte finish. The application is very simple and consists of smoothing the surface, passing a layer of paint and repeating. However, depending on the shape of the object to be treated, you will have to choose between a brush and a cloth to spread the product.
Steps
Part 1 of 4: Setting up the Workspace
Step 1. Clean the area where you need to work
Remove dirt and dust as much as possible. Vacuum, wash and / or clean every surface. Reduce the amount of residue that could adhere to the layers of the polyurethane paint.
If dust and other particles dry on the polyurethane, the surface will have an uneven appearance
Step 2. Air the room
Create a current of air that passes through the workspace to disperse the fumes caused by the paint. Open the window and install a vacuum that sucks the air out. Then, if you can, open a window on the opposite side of the room.
- Do not use a fan in the immediate vicinity of the work area, otherwise it may bring dust to the wood as you apply the paint.
- Buy a respirator with an activated carbon filter if you are unable to improve the ventilation of the room and / or if you are allergic to fumes.
Step 3. Create a work surface
If you can transport the object to be treated, spread a protective coating on the floor to protect it while working. Use a tarp, cloth, piece of cardboard, or similar material. Whatever you use, make sure it covers the underlying surface by nearly half a meter on all sides of the wood to protect it and facilitate final cleaning.
Also, make sure the surrounding area is clear of objects you don't want to damage in case of an accident
Part 2 of 4: Prepare the Wood
Step 1. Remove the old finish
Remove any pre-existing traces of shellac, lacquer, wax, enamel or varnish. Therefore, during this phase do not hesitate to move the object outdoors in order to take advantage of better air circulation and facilitate cleaning.
Step 2. Sand
If you feel the surface is particularly rough, start with a sheet of medium grit (100) sandpaper. Then use a fine-grained one (150) and then another extra-fine (220). Check the wood for any scratches between sanding. If necessary, use the extra-fine sandpaper to smooth the scratched parts.
Step 3. Clean
Vacuum the wood and surrounding area to remove any dust created by the sanding process. Use a soft brush attachment to avoid scratching the surface. Then, moisten a lint-free cloth and wipe the item to remove any residual dust left by the vacuum cleaner. Repeat with a dry microfiber cloth.
- If the polyurethane paint is oil-based, wet the cloth with white spirit.
- If it is water based, moisten it with water.
- Some use the dust cloth to dry clean wood, but be aware that this product may contain chemicals that hinder the adhesion of the polyurethane to the surface to be treated.
Part 3 of 4: Deciding on Application Technique
Step 1. Use a brush on flat surfaces
Apply the paint only once over the entire surface using a brush. With this tool you can reduce the number of layers, because it allows you to create a more consistent coverage. If you need to apply an oil-based paint, opt for a brush with natural bristles, while choose one with synthetic bristles if the product to be applied is water-based. Proceed as follows:
- Dip the brush in the polyurethane paint for about 2.5 cm to properly impregnate the bristles.
- Pass it following the grain of the wood, with long and regular brush strokes.
- After a brushstroke, slide it again on the droplets that eventually formed, in order to eliminate them.
- Start the second stroke in the middle of the previous one to reduce the risk of creating uneven spaces and areas.
- After each layer, see if droplets have formed to be eliminated.
Step 2. Use a cloth on curved surfaces
Do not use the brush on surfaces that are not perfectly flat, otherwise there is a risk that droplets will form. The cloth technique allows you to apply paint in thin layers, so you need to double the number of coats. When wiping:
- To apply the paint, fold a clean cloth into a square shape so that it is the size of the palm of your hand.
- Dip one edge in the polyurethane paint.
- Pass it on the wood, following the direction of the grain.
- Overlap each layer in half of the previous one to get even coverage.
Step 3. Spray on less accessible spots
Buy polyurethane spray paint if areas that are difficult to reach with a brush or cloth. Caution is never too much in these cases, so apply the product a little at a time to prevent it from dripping, because on the most critical areas it is more difficult to correct any errors. Be sure to cover the surrounding area with a protective sheet before proceeding.
- The polyurethane spray paint allows you to obtain very thin layers.
- Practice on a test surface to improve your use of this technique.
Part 4 of 4: Apply the Polyurethane Paint
Step 1. Mix
After opening the can, use a stick to mix the substances contained inside, which will probably have separated over time, and make the paint uniform. Stir instead of shaking it, otherwise bubbles may form and transfer to the wood, creating an uneven layer.
Step 2. Seal the wood
Use a clean container to make a two-to-one mixture of polyurethane paint and white spirit, respectively. Use a brush or cloth to apply a single layer of this solution. Wait for it to dry before proceeding.
If absolute, polyurethane varnish dries in 24 hours, but diluted with white spirit, it should take less time
Step 3. Sand again
From this point forward, always sand the wood before applying another coat of varnish. Remove any visible stains, droplets, bubbles or brush strokes using a sheet of extra-fine sandpaper (220) to reduce the risk of scratching the surface. Once done, vacuum and use a dry cloth to wipe off any residue.
Step 4. Apply the first layer
Once the wood is sealed, use absolute polyurethane varnish. However, keep pouring small amounts into a clean container instead of dipping your brush or cloth directly into the original can. Avoid contaminating it with dust or other particles that the brush or cloth could transfer.
- If you are using the brush, pass it well over the entire surface before reloading it. Eliminate any dripping drops or traces.
- Wait 24 hours for it to dry.
Step 5. Repeat everything
Once the first layer is dry, sand the surface again. Then, apply the second pass in the same way. Wait another 24 hours for it to dry. If you used the brush, two layers will do just fine. For all the points treated with the cloth or the spray, double the applications, for a total of four layers.
