how to apply polyurethane to wood floors

How To Apply Polyurethane To Wood Floors

By Fortino Rosas / November 19, 2020 / 14 Comments

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    So you’ve finished installing those hardwood floors—awesome job! But wait, you aren’t done. Do you know how to apply polyurethane to wood flooring for that awe-inspiring finish?  You wouldn’t want all your hard work to go to waste, would you?

    Polyurethane acts as a shield for your wood floors. It protects the wood from the scratches and spills that come with everyday life. Urethane is available in two varieties and several sheen levels, ranging from glossy to matte.

    The application process can be tricky, so you’ll need to brush up on your skills. Here’s what you should know before attempting a polyurethane finish.

    Should You Use Water-Based Or Oil-Based Polyurethane?

    To start with, you must decide whether to use an oil-based or water-based product. Both will protect your floors, whether you have traditional or engineered hardwood, but there are notable differences.

    Should You Use Water-Based Or Oil-Based Polyurethane?

    Water-based polyurethane goes on clear and will not alter the color of the wood. It’s also thinner than other solutions and dries quickly. You can walk on your floors within 8-12 hours of application.

    Water-based finishes are less flammable and don’t contain harmful VOCs. They won’t emit strong odors or fumes. And when it comes time to clean up, all you’ll need is soap and water.

    This type of polyurethane is the most expensive and least durable. Because these urethanes are comprised of fewer solids, you’ll need to apply several coats for maximum protection.

    If you seal your wood with a water-based product, expect to repeat the process every two years.

    By comparison, oil-based polyurethane enhances the coloring of the wood and gives it a soft glow. Due to their composition, oil-based products are thicker and take longer to dry. They do emit fumes, though, so prepare to don a face mask.

    There is an upside to this type of urethane: Oil-based products fortify the wood with a solid layer of armor. They take fewer coats than water-based poly and cost half as much as water-based products.

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    What Materials Do You Need?

    It’s time to whip out your pen and paper (the list is longer than you’d think). But, don’t worry—most of the products are inexpensive and can be found locally.

    Once you’ve decided on which polyurethane you’ll use, it’s time to research brands. It’s important to choose a brand that’s upfront about the chemicals and storage requirements. Look for a company that offers telephone support, in case you need advice.

    Unless you have one on hand, you’ll need to rent an orbital sander from your local hardware store. Be sure to buy sandpaper in varying levels. The pros recommend you purchase 36-, 60- and 120-grit to start.

    And don’t forget to grab 220 grit sandpaper-and a pole sander for use between coats. If you don’t want to buy a pole sander, you can make one out of a broom handle and a sanding block.

    You’ll also need urethane-rated brushes and a lambswool or synthetic applicator. You can use a T-bar for getting into corners and door jambs. T-bars work best with water-based formulas, so you may want to buy a roller instead.

    This project requires a shop vac, so borrow one if you need to (or check out our review of the 6 best shop vacs). Remember to pick up a respirator and some gloves. Masking tape and mineral spirits will come in handy during prep, so make sure you buy them.

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    Time To Prep

    Now that you’ve got the shopping out of the way, it’s time to prepare your workspace. This is the most crucial and tedious part of the process.

    Begin by vacuuming your hardwood floors and set yourself up to start with a clean surface. Dig into the corners and clear away any dust or cobwebs. Open some windows and let the room air out a bit.

    Time To Prep

    After you’re done with that, it’s time to start sanding off the old finish. If you’re not sure how to operate the sander, queue up some online tutorials. Start with the roughest sandpaper and work your way up.

    Don’t sand in one area too long or you’ll risk scoring the wood. Check the surface one last time for splinters or dents.

    When you’re done sanding, vacuum away the dust and wipe the boards with a lint-free cloth and mineral spirits.

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    The Application Process

    Now you’re ready for the main event. Start by stirring the polyurethane with a paint stick. Never shake a can of polyurethane or you’ll sabotage the finish with air bubbles.

    Load your brush or applicator with poly and tap off any excess. Pick a corner and start working about a foot out, going in the direction of the grain. Use long, overlapping strokes to ensure an even coat.

    Look for signs of dripping and correct these spots before they dry. Wait a few minutes after the first coat, and check one more time for blemishes or places you may have missed. Apply the polyurethane to the corners and blend it into the boards.

    Let the first coat dry completely before restarting the process. Be sure to read the manufacturer’s guidelines on drying times. Once the floor is dry, you can wet sand any drip marks or imperfections.

    Repeat the application as needed, allowing the floors to dry between coats. Most wood floors require 2-3 coats, but it’s best to check with your flooring manufacturer before calling it quits.

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    FAQs About Applying Polyurethane To Wood Flooring

    What Is The Best Applicator For Polyurethane?

    The best applicator for applying oil-based polyurethane to wood floors is a lambs wool applicator. This accessory is effective in spreading the polyurethane evenly across the surface, much more so than using a paint roller, although a roller can work with water-based products.

    Before using a lambs wool applicator, remove hair, lint, and other debris from the wool’s surface. An easy way to do this is to cover the surface with painter’s tape or anything similar and then ripping it off. All the loose debris will stick to the tape, so it doesn’t end up on your floor during application.

    For corners, skirtings, and other nooks and crannies, use a natural bristle brush. It’s up to you whether you find a 3” or a 5” brush most comfortable to work with. Just use a finishing brush and not a regular paint brush.

    How Do You Apply Water-Based Polyurethane To Hardwood Floors?

    When you work with water-based polyurethane, use a synthetic bristle brush in the corners of the room, rather than one with natural bristles.

    For the center of the room, you can use a roller or trim pads. Make sure it’s a synthetic pad, though, since this won’t retain the polyurethane, making it easier to apply.

    In terms of how to apply polyurethane to wood flooring, start in the corners with your brush and then apply it to the center with your roller. Just remember to plan in such a way that you have a place to exit the room without stepping on the wet floor.

    Wait for the floors to dry. Drying times vary based on circulation and temperature. Usually you can apply a new coat of water-based polyurethane for wood floors after three hours.

    When using a water-based product, apply the polyurethane as many as four times for best results.

    How Many Coats Of Polyurethane Should You Put On A Wood Floor?

    The number of coats you apply depends on the type of product you’re using. For oil-based products, it’s usually enough to have two coats or a maximum of three. For water-based polyurethane-finished wood floors, plan to apply up to four layers.

    It’s best to apply more coats than settle for less. Remember, each layer adds another barrier of protection. You can settle for fewer coats, but in doing so you may end up refinishing the floor sooner than you think. Instead, put in the time now and apply the polyurethane one more time, so you enjoy more longevity.

    Can I Use A Rag To Apply Polyurethane?

    Yes, you can use a rag as an option for applying polyurethane to floors. It’s especially a helpful method if you’re working on a vertical surface or have a contoured area you need to varnish.

    Just note that you must be meticulous in your process, or you won’t have an even finish. Don’t place too much polyurethane on the rag to start with. Too much product can result in a raised grain. Also, work with the grain when applying.

    For best results, you can also look for wipe-on polyurethane products designed to be applied with a cloth. Note that these products are often much thinner than some other polyurethane products. So, when you’re planning how to put polyurethane on wood floors with a rag, schedule enough time to apply as many as four coats.

    Can I Use A Foam Brush To Apply Polyurethane?

    Yes, you can certainly use a foam brush to apply polyurethane to hardwood floors. You’ll appreciate that this type of brush rarely drips product on the wood flooring you’re working on. Only when you apply pressure will the polyurethane leave the foam.

    It’s also easy to have neat results. If there are any bubbles in the polyurethane layer, you can eliminate them by simply making another stroke over the same area.

    When planning how to apply polyurethane to wood flooring, some people prefer foam brushes to bristle brushes because you can simply throw away these cheap applicators once you’re done. That minimizes the cleanup time.

    What Is The Best Polyurethane For Wood Floors?

    Different polyurethane products are best for different scenarios.

    When wondering how you polyurethane hardwood floors in high-traffic areas such as an entrance hall or an office space, you’ll need oil-based polyurethane. This type is easier to maintain than water-based products and it’s more durable too. Oil-based products are also more water-resistant, so soap and water spills won’t easily damage the floor.

    A water-based polyurethane layer on your wood flooring will be your ideal option if you’re looking for a faster solution. These products dry much faster than oil-based polyurethane, so you don’t need as much time to complete your project.

    You’ll also find that water-based products have less odor and won’t release many volatile organic compounds. These VOCs can be harmful to the environment, making a water-based coat on your wood floors a more eco-friendly option.

    Is It Necessary To Sand Between Coats Of Polyurethane?

    Yes, it’s best to sand your hardwood floors between the successive coats of polyurethane you apply. Since each coat takes a while to dry, there’s a lot of time for dust to settle during the drying times. You’ll need to remove this layer so that hair and other particles don’t permanently form part of your flooring.

    The other reason why sanding is so important is because it creates a rough surface that makes bonding easier for the next layer. Sanding also affects how smooth your floor will be. After the first layer, you’ll need to do considerable sanding to guarantee smoothness. For the other layers, sanding will be less intensive.

    Give enough time for the floors to dry, so you’re sure it’s ready to sand. You’ll use different sanding methods for different polyurethane products. An oil-based layer requires steel wool, while you can use an abrasive pad for water-based polyurethane.

    How Do You Apply Polyurethane Without Creating Bubbles?

    When learning how to apply polyurethane to wood flooring, what you use as well as your technique will determine whether there will be bubbles in your polyurethane layers. When learning how to put polyurethane on wood floors, you need to start with the right applicator, such as a finish brush and not an ordinary paint brush. A finish brush will apply a thinner coat than a paint brush, which would deliver globs of product. The thinner the layer, the less chance you will have of creating bubbles.

    Before you brush on the polyurethane, soak the brush in mineral spirits. You can also use water. This will displace the air caught between the bristles, so it doesn’t create bubbles once you start applying the polish. Gently brush it across a piece of newspaper to dry it out before use.

    Thinning the polyurethane can also help. Use mineral spirits for oil-based polyurethane and water for water-based products. Use a ratio of three parts polyurethane to one part of your thinning material. Gently stir in the solvent; never shake the products to mix, because shaking will create bubbles even before you start.

    When you start applying the polyurethane, practice applying thin layers in gentle strokes.

    What Is The Best Temperature To Apply Polyurethane?

    The perfect environment for using polyurethane is 70°F. This will ensure drying times don’t become too long.

    If the temperature is as low as 55°F, it can cause water-based polyurethane to form a texture that resembles orange peel. With oil-based products, lower temperatures aren’t too problematic but will slow down oxidation processes. But you can still work in temperatures as low as 60°F.

    If you work in much higher temperatures, the layers will simply dry quicker, especially with water-based polyurethane.

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    To Sum It Up

    Finishing your wood floors with polyurethane isn’t rocket science, but it IS hard work. Applying the product requires a combination of ability and knowledge.

    As with any home improvement project, careful selection and proper preparation will affect your results. Take the time to practice your technique on scrap wood. The most important thing to remember is to let your floors dry before sanding or walking on them.

    While it may feel like a never-ending process, take heart in the fact that your wood floors are timeless. With regular maintenance, they’ll look beautiful for years to come.

    Have you tackled a polyurethane application? Tell us about it in the comments below.

    About Fortino Rosas

    Chief Floor Critic, 32 years of experience in flooring installation and sales

    Fortino Rosas is an independent flooring contractor with 32 years of experience in residential and commercial flooring installation and sales. He joined the Floor Critics team to share his expertise with our readers. Fortino has acquired vast knowledge and skills in the areas of product selection, space planning, and installation. He has installed flooring in residential, government, and commercial office projects in the Midwest. Visit Website.

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