How To Apply Clear Finish on Wood
"Applying clear finish on a wood project is an extra step, but it’s always worth the time. A clear finish provides a protective coat for your wood that guards it against stains, water damage, and natural wear and tear."
Materials
Staining and finishing are key steps that will transform your DIY project into a finished piece that will be a beautiful addition to your home. Tackling any new experience can be intimidating, and while the directions on the can are vital for success, there’s nothing quite like getting to learn from the experience of a real person. Today I’m going to walk you through the basics of applying finish to your DIY projects, and will share some advice from my personal experience along the way.
Clear finish can be applied over stain or directly to raw wood. It’s an extra step, but it’s always worth the time. A clear finish provides a protective coat for your wood that guards it against stains, water damage, and natural wear and tear. Applying a water-based clear coat to light-colored raw wood can stop the natural yellowing process of the wood, which helps to keep those cooler tones in-tact. Finish also helps make dusting easier down the road—I’ve found that pieces without a clear coat are very difficult to dust because of the roughness of the natural fibers in the wood.
Today, we’re using a polyurethane clear finish. It’s a great finish to use when you’re starting out—it’s easy to apply, dries relatively quickly, and gives you options when it comes to sheen and tone. Similar to paint, you’ll be able to choose any sheen you’d like (gloss, semi-gloss, satin, matte, etc.). There is no difference in durability between the various sheens, but know that gloss may highlight imperfections, while matte is more likely to cover them.
There’s a lot to know before you dip your brush, so let’s get to it!
Step 1: How to choose the right finish
If you’re finishing a piece you’ve previously stained, you’ll want to make sure the finish you choose is compatible with the stain you’ve applied. Picking a clear finish with the same base (water or oil) and from the same brand as your conditioner and stain is always the safest way to go. If you’re using a different brand, it’s best to do a test swatch on a scrap piece to make sure they’re compatible. If you’re mixing bases, just make sure that your stain has completely dried before testing. Today, I’m using Varathane crystal clear polyurethane in a satin sheen. This is my go-to finish product!
Water-based vs. oil-based finish
There are a number of differences between water-based and oil-based polyurethanes, but the biggest for me is the clarity. Oil-based polyurethane has a distinct amber hue that will darken over time, while water-based polyurethane is truly “crystal clear” (it may look milky in the can, but it dries completely clear). This isn’t a big deal if you’re working with a darker stain, but if you’re applying a clear coat to a whitewashed or gray stain, or to light-colored wood that you don’t want to yellow, then water-based is definitely the way to go.
Other differences to consider are that oil-based is generally less expensive and requires fewer coats, has a stronger smell, and takes longer to dry, while water-based polyurethane dries harder and thinner. When it comes to clean-up, water-based can be cleaned up with water while oil-based requires mineral spirits.
Spray-on vs. brush-on application
Spray-on may seem like the obvious direction to go because it’s a lot quicker—but similar to spray paint, a spray-on finish doesn’t create the same thickness that a brush-on finish does, and it just won’t be as tough. That being said, spray-on does go on smoothly, while a brush is likely to leave some brush marks (these brush marks are made less noticeable by brushing on the finish in the direction of the grain).
Personally, I like to use brush-on for long-lasting furniture pieces like tables, chairs, bed frames, and moulding. I would use spray-on for more intricate pieces or projects that I don’t want to take the time to hand brush—things like outdoor games, a wood doormat, and the like. I choose spray-on polyurethane when I think, “there’s no way I would take the time to brush on polyurethane.”
Step 2: Prep work
Before applying a clear finish, it’s important to prepare. Start by picking a location. Choose a spot that’s relatively dust-free and out of the way of children, pets, and weather. Read the label of the product you’ll be using and stay within the recommended temperature range to ensure everything dries correctly, or at all. And because most finishes have some odor, you’ll want to pick a spot with good ventilation.
Next, lay a drop cloth to protect your work surface. I prefer a plastic-backed canvas cloth because the fabric absorbs finish, but the plastic underneath provides a firm boundary between your work surface and your work.
Lastly, it’s important to remove dust from the wood’s surface. There’s always dust in the air, and if you’ve just sanded there will be very fine sawdust on your project. You can remove dust with a tack cloth (which is a cloth coated in wax), a vacuum, or a rag dampened with water or mineral spirits. Whichever method you prefer, check your directions to make sure it’s compatible with the product you’re using. For example, tack cloths shouldn’t be used before applying a water-based finish because residue left by the tack cloth can get in the way of the finish going on evenly.
Step 3: Apply finish
Before you begin applying finish to a project, you’ll want to make sure that any stain you’ve applied has completely dried. Stir your finish well, but don’t shake as this can cause air bubbles that will then end up on your finished piece. Over-brushing can also create bubbles.
Using a high-quality bristle brush (natural bristle for oil-based finishes, synthetic bristle for water-based finishes) or other recommended applicator, apply finish in one direction with the grain so as not to raise wood fibers and to hide brush strokes. Remove any drips at the bottom of your wood while still wet. Allow the finish to fully dry in between coats, but make sure not to exceed any time constraint mentioned in the directions on the can. Exceeding the time constraint usually requires sanding the finish down before applying the next coat, so if you’re not planning on sanding between each coat (see step three), applying within the time limit will result in less work. Applying multiple coats of a clear finish can be tricky because the wet finish becomes more difficult to see on top of the dried finish. Placing a light at the surface level of where you’re applying can make the parts you covered and the parts you missed easier to see. And if you’re working with a more complex project that has a lot of surfaces, I highly recommend coming up with a pattern that you follow during each coat so you don’t accidentally coat one part twice and miss another part entirely.
Step 4: Sanding
It's normal for directions to call for sanding between every coat (once it's dried), or before the final coat, and it can really make all the difference in a project. Sanding clear finish takes a fraction of the time it takes to sand wood and it’s always, always worth it. I’ve found that when I don’t sand my finished pieces, they can’t be dusted. That’s because sanding before the final coat removes any wood fibers that have risen out of the polyurethane finish, and these tiny fibers roughen the surface enough to make removing dust nearly impossible. Not to mention—that smooth surface you get from sanding is so rewarding, it’ll make you feel like a pro. Sanding between each coat (if that’s what your finish product instructs) helps the next coat adhere to the previous one, so skipping sanding could be the difference between your finish holding up for decades to come, or needing to be redone a whole lot sooner. So just remember, sanding will save you time and heartache later.
If you do decide to sand (or your instructions call for it), you’ll generally want to use 400+ grit sandpaper. Wet sanding may also be required by whatever product you’re using, and though it may sound intimidating there's no difference in technique from dry sanding. Just make sure you have a piece of sandpaper marked for wet sanding. Be sure to remove any dust from sanding before continuing with coats.
Always follow the directions on the can to allow your final coat of finish to fully dry before using your piece. Factors like humidity, temperature, coat thickness, and quantity of coats may slow down the drying time, so use your best judgment (when in doubt, always err on the side of more drying time).
Going the extra mile in the finishing process can sometimes be the step that transforms your DIY project from something you’re proud of to something your friends won’t believe you made yourself. We hope this break-down helps you put the finishing touches on your projects with ease! For more tips on staining your pieces, check out how to stain wood and how to condition wood before staining.
