Wood finishing is important if you want to protect the wood from a harsh environment while keeping insects attack at bay. There are so many wood finishes available today with varying levels of effectiveness, look, cost and application.
One popular wood finish is polyurethane which is used on the wood to reduce the effect of wear and tear.
Polyurethane is one of the most effective and durable finishes out there. It comes in carrying forms with different methods of applications. Wood finishes like polyurethane are different from wood staining, which only affects the look of the wood.
Polyurethane finishes are made from urethane polymers but do not contain urethane. The finish is a clear film.
No matter what the project may be, whether it is a cabinet, a box, or a wooden board, covering it with polyurethane will increase its lifespan. Many people familiar with wood finish understand the vital role finishes like polyurethane play; however, not many people know how to apply it effectively. Before we go into details on how you can apply polyurethane, let’s look at the major types available.
Types of Polyurethane
There are four types of polyurethane wood finishes available with differences in how light is reflected off it.
1. Matte Polyurethane
This type of finish has the lowest level of sheen and reflects no light off the surface. Its dull look may be an attraction for some and a turn-off for others.
2. Satin Polyurethane
This type possesses the next level of sheen. It is not dull and not shiny as it portrays a good blend of the two extremes. This type of polyurethane is also the most popular option today, as it hides dirt and scratches well.
3. Semi-gloss Polyurethane
It is the next in luster intensity with a shiny surface as it reflects a lot of light. It does require a lot of maintenance as it also shows dust and scratches easily.
4. High Gloss Polyurethane
At the top of the luster, intensity is this high gloss polyurethane that shines so bright and shows every dirt and the tiniest of scratches. You’ll need a lot of maintenance if you use this finish. The finish is perfect for exotic wooden pieces.
Oil-Based or Water-Based Polyurethane?
Polyurethane usually comes in two forms, oil-based and water-based. You may be thinking about which of the two forms of polyurethane is best for you since both of them are quite popular today. They possess unique properties that set them apart.
Depending on what you intend to use the finish on and how you’ll like it to look, feel and work, any of the two forms of polyurethane may be the most suitable. Oil-based are thick, easy to apply since they do not run, and contain more solids which ensure a few coats are enough.
One of its biggest drawbacks, however, is its drying time, as it takes a long time to dry, giving more time for harmful insects to enter the finish. This form of finish is susceptible to brush marks. If you want the finish to have a warm color to it, oil-based is your go-to option.
Water-based polyurethane, on the other hand, dries quickly with less odor and a better spread. However, it is susceptible to watermarks and raises the grains of the wood. Applying this form of polyurethane requires a lot of patience as it drips. You’ll also need more water-based coats. If you want a clear finish with no significant color change, water-based should be considered.
Materials Needed to Apply Polyurethane to Wood
- Orbital hand sander
- Foam brush
- Chemical resistant gloves
- Stirring stick
- Tack cloth or mineral spirits
- The chosen polyurethane
- Sandpaper or sanding block
- Drop cloth
Steps on How to Apply Polyurethane to Wood
After getting the above materials ready, you can follow the steps below to apply polyurethane to your wood.
Step 1: Prepare Your Workspace
This involves cleaning the area you’ll be working in, ensuring no particles and dust can stick to the finish before it dries. You also want to ensure cross ventilation in the area so the fumes can leave as quickly as they form.
You might be tempted to install a fan directly over the area to boost ventilation, but this will only raise more dust and blow particles onto your finish.
If the workpiece can be moved easily, place a drop cloth underneath it, ensuring the cloth extends more than the base of the wood. This will ensure the finish does not come in contact with the ground.
Step 2: Prepare the Workpiece
The preparation done on the workpiece in anticipation of the finish will set the ground on the effectiveness of polyurethane after application. While preparing the wood, you can take it outside for better ventilation. Clean the surface properly, ensuring it is smooth and even. Scrape off previous finishes, paint, latex, varnish, and shellac on the surface.
Using sandpaper, carefully smoothen the wood, ensuring the surface is fine and smooth. Use a soft brush to clean and then a dampened lint-free cloth to wipe the surface afterward in a circular manner. If you are going to use an oil-based polyurethane, dampen with mineral spirits or water if you’ll be using water-based.
If you want to change the color of your wood at the end, you should apply a stain to the wood and allow it to dry before moving to the next step.
Step 3: Choose the Most Suitable Polyurethane and Prepare it
You have to consider the differences and your preference before choosing the polyurethane finish to use. For oil-based, you’ll need to thin it with mineral spirits to reduce brush marks and make it easier to apply. Stir the polyurethane with the stirring stick but do not shake it as it can create bubbles.
Step 4: Apply the Polyurethane of Your Choice
Applying polyurethane is different from paint application and should be done carefully. One of the most suitable appliers is a foam brush as it does not leave brush marks on the surface.
Dip the foam brush halfway into the polyurethane and then allow it to drip before brushing it on the workpiece. Apply in one clean wipe slowly and steadily at first to understand how it sticks. Apply row by row, overlapping just slightly, so you do not leave any gap.
Apply the first coat and avoid brushing it too much, so you do not significantly reduce the polyurethane on that area. Allow the coat to dry and sand lightly with 320-grit sandpaper. Apply the next coats, ensuring you allow each coat to dry lightly before sanding. The more coats you’ve placed, the less sanding and finer sandpaper is required.
The final coat can be made to dry faster and look better by using an aerosol polyurethane that is sprayed on the surface or by making use of wipe-on polyurethane.
Step 5: Allow it to Dry
After the final coat, you have to leave the finish for at least 24hours before you handle the workpiece. This is to ensure you do not leave fingerprints on the surface.
It may take several days to cure enough to be ready for use. To completely cure and be free from any smell, it may take up to 28 days.
The temperature and humidity of the area will determine the drying time, with a more humid area requiring more drying time.
Tips for Applying Polyurethane
Here are tips to follow to improve your polyurethane application and ensure a better finish. We have compiled this in a questionnaire for a better understanding.
How to Start the Application?
Always start the application at the end of the piece. This will make it easy to overlap and allow you to do this in the shortest possible time before it starts to dry.
How Many Coats do You Need?
Anything from 3 to 5 depending on preference and the form of polyurethane used. Oil-based require fewer coats than water-based ones.
Should You Apply to Unseen Surfaces?
Unseen surfaces like under the table and inside cupboards are often neglected, but they also need the finish to protect the wood from warping or soaking up too much humidity. Apply a few coats in unseen places.
How to Keep After Appling?
Keep the Surface Flat Where Possible. By applying on a flat surface, the finish levels evenly, and dripping is reduced as against when it is vertical.
Make use of thinner coats and wipe on polyurethanes when applying on vertical surfaces.
Applying polyurethane is more than rubbing the finish on the surface and waiting for it to dry. It involves careful planning and preparation; thus, the finish is level and clean, and you get the right reflection based on the type you choose.