How to Apply Water Based Polyurethane to Wood Floors

Here’s something I never thought I would say: every woodworker needs to learn how to apply water-based polyurethane to wood floors!

Considering how sub-par they once were, that’s really incredible! Just a decade ago, you couldn’t rely on water-based polyurethane for dining room tables, let alone wood floors. They weren’t as durable as oil-based polyurethane; they were tricky to apply and just way too expensive.

But I’m glad to say everything has changed. Well, water-based polyurethane is still more expensive, but it can actually save you money if you follow these steps correctly.

How to apply water based polyurethane?

To apply water-based polyurethane, start by sanding your project. Then, apply a very thin coat of polyurethane with a fine brush, foam pad, or cloth. Once the first coat dries, sand it lightly with a fine-grit sandpaper and apply a second coat. Work along the grain and don’t apply excess polyurethane.

Tools you Need

• Belt sander
• Edger 
• Scraper 
• Natural bristle brush or foam brush
• Wood floor filler*
• Putty knife*
• Water*
• Trowel* 
• Rug (Here are the tips for applying polyurethane with a rug)
• Buffer
• Mineral spirits
• Sandpaper block
• Trim pads 
• Walk-off mat
• Surgical booties
• 220 grit sandpaper*
• Cut-in pad
• Vacuum cleaner
• Tack cloth and mop
• T-bar
• Microfibre roller*
• Water-based Polyurethane – matte, satin, semi-gloss or high-gloss
• Respirator 

The items with an asterisk* are optional, depending on the condition of your wood or any problems that arise during the application process.

You will need the respirator when sanding, but not during the application of the finish because water based formulas doesn’t have a strong odor.

Also Read: How to Make Floor Less Slippery

How to Apply Water Based Polyurethane to Wood Floors – Step by Step Process

Step 1: Sand the Floor

The first thing you need is a smooth, level surface. You will need a belt sander and a very coarse grit of sandpaper.

As you are using a large machine that can very quickly mess up your hardwood floors, you need to ensure you choose the correct grit.

If you are working on a hard floor like maple, you may need 36-grit sandpaper. For softer wood, first test 50-grit sandpaper on an inconspicuous spot on the wooden floor.

If it doesn’t level the wood floor well enough, drop down to 36-grit. If the floor has paint on it, you might need to go even lower. Once you find the right grit, sand the whole room with the belt sander or any suitable alternative.

Always sand with the grain. The video above shows in detail the correct procedure for using a belt sander.

Step 2: Use an Edger

A belt sander is a large, quick, and effective tool, but it has its limits. Where it ends is where you carry on with an edger.

An edger can sand right up to the wall without causing any damage to the borders or any paint on the walls. Just as with the belt sander, test out grits to find the right one.

Once you do, sand with the grain and ensure you feather correctly, so you don’t leave any trails or patches.

An alternative tool is the orbital palm sander. It is smaller than the edger, so it can get even closer to the wall and further into corners.

Step 3: Clean the Floor

Now it’s time to whip out your vacuum cleaner and carefully go over every inch of the floor. Nothing ruins polyurethane like dust. So you have to clean the wood floor before polyurethane.

The vacuum cleaner should follow the same path as the belt sander. As you do so, take notice of any parts of the floor that appear more or less level than the others. Use a lumber crayon to identify any patches before the next cut.

Step 4: Make a Second Cut with the Belt Sander

Again? Yes, again. When working on hardwood floors, you might need to make three cuts with a belt sander and two with the edger. Each cut will ensure that the floor is more even and that all imperfections are gone.

For every new cut, use a finer grit and follow the proper grit sequence: only skip one grit level at a time.

So, if you started with 36-grit, move on to 50-grit, then 80-grit. This will gradually reduce the depth of the cut, making the floor smoother.

Also, reduce the pressure you apply with every new cut and walk slightly quicker each time.

Step 5: Scrape the Edges

By now, you would have noticed that the floor corners haven’t been sanded at all. This is because edgers are great for the length of the wall but not so good for corners.

Use a scraper or a synthetic bristle brush to get into the spaces the edger can’t reach. You can also use a sanding block for this. Scrapers tend to work a bit faster, so you can start with that then move to the sanding block.

You may need several levels of grit to remove the marks left by the scraper and the edger. Start from the roughest grit as usual and progress to the finer ones.

Step 6: Vacuum Again

Just a heads up, you should always vacuum in-between cuts. It is important to clean the floor thoroughly, especially if you are going to apply filler before the final cut.

You may also use a tack cloth after you vacuum the floor to make it even cleaner. However, this might be time-consuming, so I’d say save the tacking for later.

Step 7: Fill Any Cracks if Necessary

As wood gets older, it will naturally develop some cracks. However, not all of these have to be filled. For example, if you are working in winter, there will likely be seasonal cracks caused by low humidity.

When summer comes, the wood will expand as humidity increases and close the gaps. But if the holes were caused by natural effects in the wood or damage, you can fill these up.

First, gently stir the wood filler to make it easier to apply. You might need to add some water to improve the consistency. Then put the right color or combination of colors to get the filler to match the wood.

If there are only a few areas with holes, use a putty knife to apply the filler. If the whole floor needs to be filled, you will need a trowel.

Step 8: Leave the Filler to Dry

Leave the filler to dry overnight. The filler on the surface will dry quicker, but don’t let it deceive you. The filler beneath the surface takes much longer, which is why you should wait at least a few hours.

If you try sanding when the filler underneath isn’t dry, it will come back up to the surface and ruin your all your hard work, and you will have to repeat the process.

Step 9: Final Cut of Sanding

For this final process, you should vacuum any leftover debris from the filling stage. Then, once the floor is moderately clean, it’s time to sand again.

Use a finer grit yet again, according to the sequence you are following. You may start with the belt sander, then move on to the edger as you did before, or vice versa – either way works fine for the final cut. 

If you don’t have to fill any cracks in the wooden floor, you can scrape the floor after this final cut. That way, you won’t have to scrape the floor twice.

Once you are done, give the floor one last thorough vacuuming before you buff.

Step 10: Buff the Floor

Now it’s time to buff the floor. You can use the Bona multidisc or whatever buffer you are comfortable with, as long as it can eradicate the edger marks and other inconsistencies in the sanding.

Yes, getting a buffer means you have to hire yet another machine, but this is the one you shouldn’t skip.

You may choose to sand the floor by hand or with the grit paper attached to a mop instead of an electric sander. But unless you have mechanic precision, there will be a few errors.

These errors or differences in sanding patterns, sanding depths, etc., will be corrected with the buffer. You will need to run about two or three cuts with the buffer.

As you can see, finishing a floor takes a lot of time and effort. Videos on YouTube might make it seem like a day job, but it really isn’t. However, once you master the process, you’ll be able to get a decent wage from each job.

So, let’s move on.

Step 11: Clean the Floor Again

It’s time to bring out the vacuum cleaner once again, and this time, the cleaning will be extensive.

After going over the main floor, use the crevice tool on the vacuum cleaner to remove any dirt along the edges or anywhere dirt can hide.

Remember I said at the beginning that applying water based polyurethane is easier for floors than applying oil-based polyurethane, and here’s how. If you can keep dust away from the wet poly, you won’t need to sand between coats!

I mean, you’ve sanded the floor three times already and hit it with a buffer twice; aren’t you tired already? So, keep the floor as clean as possible, and you can wrap up early.

After the crevice tool, take a damp tack cloth and run it across all of the sides of the floor, making sure you dig into any holes or corners. This is very important because you don’t want the poly to mix with this dirt and ruin the floor.

The next step is to run over the entire floor with a dry tacking cloth. After this point, you should wipe your feet with the walk-off cloth (use a clean, white towel) and wear your booties.

Here is a more detailed guide on how to get dark urine stains out of hardwood floors.

Step 12: Prepare the Water Based Polyurethane

The first step here is to stir the polyurethane with a stick gently. Some finishes come in a bottle, so tilt it back and forth to mix it up, but not too aggressively.

Depending on the brand of water based polyurethane you are using, you may or may not need to thin it with water. However, if this is your first time, you might want to thin it with just a little bit of water, no more than 10 percent.

Thin coats are easier to apply than thicker ones – if you make any mistake with a coat, it will also be easier to correct.

The final preparation step is to strain the poly. Water based finishes will sometimes have a few clumps, which don’t dissolve during application. So, it’s important to strain it before use.

Step 13: Prepare Your Applicators

Whether you are using a synthetic applicator or not, you need to rinse them out and then use a cloth to absorb the moisture.

Do this for the T-bar, microfibre roller, foam brushes, and the cut-in abrasive pad. If there is too much moisture on the applicators, it will mix with the polyurethane, and the finish will be uneven. Too little moisture, and the applicators will absorb too much polyurethane.

So, make sure they are just damp. Another benefit of rinsing them is to ensure there is no lint coming off them. Roller lint is a nightmare you don’t want because you will need to lightly sand between coats.

Related read: How to clean urethane paint brush.

Step 14: Apply the First Coat

Start on the far side of the room and pour a generous amount of polyurethane along the edge. Use the cut-in pad to get the water-based polyurethane to the edge of the wall and spread some of it inwards so that the person with the roller or T-bar doesn’t have to touch the wall.

The tool you use will depend on the floor. For strip floors, use a T-bar. But for parquet and any other complex type of flooring, applying polyurethane with a roller is much better.

Get the T-bar out and begin to apply the poly away from the wall, feathering back. You should apply the polyurethane with the grain and don’t put a lot of pressure on it – the application should glide.

Try not to allow puddles to sit on the floor for too long. Water based poly dries significantly quicker than oil-based products, so you have a maximum of five minutes to spread it out before the puddles set.

This really is a job for at least two people, so that one person is pouring the finish and using the cut-in pad while the other uses the roller.

If there is any extra product on the floor when you are done, simply soak that up with a clean cloth, but first, check for dirt. If there is any debris in the leftover finish, soak it up and then apply new polyurethane on that spot and use the cut-in pad to level it.

Always plan your application to start at the end of the room and work your way towards the door. You don’t want to back yourself in a corner and then walk all over the wet polyurethane. That will definitely cause you to have to sand before your next coat.

It is best to apply the finish when there is natural sunlight, as it makes it easier to spot any patches.

See also: The difference between 1/2 vs 3/8 nap rollers.

Step 15: Let the First Coat Dry, and then Tack

What you’ll really love about water-based polyurethane is how quickly it dries. Within two hours, you can be ready for the second coat. But can I apply water-based polyurethane over oil?

After the new coat has dried, inspect it for lint, air bubbles, and puddles. It is typical for water-based polyurethane to raise the grain of the wood, but this isn’t a problem to concern yourself with at the moment.

If there are no mistakes, tack the floor and apply the second coat. As long as you apply the second coat within ten hours, it will adhere to the previous one. 

However, if there are bubbles or lint, you will need to use 220-grit sandpaper to eliminate the errors. You will then tack the floor to get rid of any dust and then apply your second coat.

Repeat these steps and add more coats until you have a perfectly smooth finish. Due to the quick drying time, the entire exercise can be done in just a few days. 

Read our guide on How long you should wait between coats of polyurethane on hardwood floors to avoid blunders.

FAQs

Do I Have to Stain the Floor Before Applying Water-Based Polyurethane?

No, you don’t have to stain the floor before applying water-based polyurethane or any other type of polyurethane. Staining makes the wood darker and can help bring out its natural beauty.

However, staining does not protect the wood, so it is not a necessary step but rather a personal choice. If you are happy with the color of the wood, don’t bother straining.

Whether you stain the hardwood floor or not, polyurethane does an excellent job preserving and protecting the floor from dents, water, pet urine, and scratches.

When you decide to stain the wood, use water-based polyurethane over oil-based stain.

Do I Have to Apply a Sanding Sealer Before Using Water-Based Polyurethane?

Unless the manufacturer asks for it, you don’t have to. Sanding sealer helps finishes adhere to the wood better while also providing maximum protection to the floor.

However, some water-based polyurethanes stick to the wood floor just fine without it. Always read the manufacturer’s instructions before you apply polyurethane of any type.

What is the Best Applicator for Water-Based Polyurethane on Floors?

The right applicator is a T-bar which gives the smoothest application of water-based polyurethane on wood floors. Unlike rollers, T-bars rarely leave puddles of the water-based finish behind; everything flows together thanks to its snowplow method.

Some experts like to apply the first two coats with a roller, sand the floor and finish off with a T-bar.

One problem with applying poly with rollers is that they sometimes absorb too much moisture and can cause bubbles to appear on the surface, especially if you don’t feather properly.

T-bars come in 12-inch, 18-inch, and 24-inch. The 12-inch is probably the easiest to maneuver and is ideal for most homes.

If you don’t have a T-bar or are working on a parquet floor, use a microfiber roller. Of all the rollers, they absorb moisture the least, making them ideal for water-based finishes.

How Many Coats of Water-Based Polyurethane Should I Use on Wood Floors?

How many coats of polyurethane for floors? Okay, you need at least three coats of water-based polyurethane on floors. Floors go through a lot of abuse over time, and you don’t want to have to refinish them often. Applying polyurethane at least three coats will give you the best protection, whether the wood has been stained or not.

If you apply the sanding sealer first, you might only need two coats of water-based polyurethane. Also, don’t feel as though you have to stop at three coats. If the floor isn’t smooth or you had to sand the third coat, apply another one and keep going until you are happy with the finish.

Related read:

How to put polyurethane over lacquer.

Can I put polyurethane over shellac?

Which Water-Based Polyurethane Finish Should I Use on Wood Floors?

When applying water-based polyurethane on wood floors, stick to either the satin finish or the semi-gloss finish. The matte finish really doesn’t look that appealing and is pretty unpopular. On the other hand, the high-gloss finish looks great, but it tends to show scratches and dents easily.

Pick any of our recommendations for the best water-based polyurethane for floors because we’ve spent hours researching the products so you don’t have to.

Finally, only use a high-gloss finish for a floor that won’t see a lot of traffic.

Is Oil-Based Polyurethane More Durable Than Water-Based Polyurethane?

Not necessarily. Many modern water-based polyurethanes are just as durable as oil-based polyurethane. There was once a time that water-based polyurethanes didn’t last long, but that is no longer the case.

What impacts their durability now is the manufacturer and how the finish was made and applied. Of course, if you apply too thin a coat, it won’t last long. However, this is true of both oil based and water-based poly.

How to Apply Water-Based Polyurethane to Wood Floors Without Bubbles.

If you follow all the steps highlighted above, you won’t need to worry about any bubbles forming.

Now, here’s our guide on how to apply polycrylic that you should definitely have a look at.

How to apply water-based polyurethane Summary

Learning how to apply water-based polyurethane to wood floors the right way can save you a lot of time and make you a lot of money.

Yes, the polyurethane itself is more expensive, but the drying time is much faster, and you don’t need as much sandpaper.

Evidently, water-based polyurethane is the best wood flooring coating because it is more environmentally friendly and easier to clean than oil based products. It is also less likely to cause problems with allergies or asthma.

Plus, finishing the job quicker will allow you to move on to the next one.

Let me know what you think about this tutorial and how you plan on using it for your next project.