Is Polyurethane Waterproof? Here’s the Truth!

Ever wondered if polyurethane can be your go-to for waterproofing? Dive in to unravel the mystery!

One of the questions I get answered the most in my woodworking career is ‘is polyurethane waterproof’.

So today I am ready to share an answer to this question with you. 

Polyurethane is the perfect way to safeguard the surface of your wood and let its true beauty come through. In my job, I use polyurethane a lot.

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They give perks that make items stronger, letting them last longer. But there are a couple of things you need to think about and understand when handling this kind of information. 

So, let’s find out, Is polyurethane waterproof?

No, polyurethane is not waterproof but it is water resistant. This synthetic resin dries on the wood, forming a tough protective coat that cannot be damaged and will not be discolored by mold or fungus.

But there’s a lot more to know!

Polyurethane makes it harder for water to get into the wood as well. 

In this article, I’ll tell you the truth about whether is polyurethane waterproof how to protect wood with polyurethane, water, and a lot more. 

Let’s get to it!

Does Polyurethane Make Wood Waterproof?

No, no amount of polyurethane can leave wood waterproof, no matter how many coats you put on. 

However, I know that it makes a tough layer on the wood’s surface that keeps water away but doesn’t cover it fully. 

In my experience, after you put a new layer of polyurethane on the wood, it’ll seal the wood and keep water away for a while. 

However, the wood’s regular change in size makes the polyurethane coat weak in a lot of places, which lets water in through. 

The item will keep keeping water away for quite some time without having to be re-coated. But plenty of water will pool on the top of the coating to get into the wood. 

So, the easiest way I take care of polyurethane-coated surfaces is simply to wipe them clean as quickly as they get dirty.

Can Polyurethane Protect Wood from Water?

Yes, polyurethane builds a tough coating on the top of your wood that keeps water and moisture away. 

Although its protective layer has small cracks in it that let a little water in, polyurethane does a great job of keeping water away and protecting my wood. 

The tiny cracks in the form of just one layer of polyurethane make it less resistant to water. 

With each layer you add to the surface, the coat gets stronger and less weak. 

The wood is better protected the more coats of polyurethane you add to it. I suggest that you put about three coats of polyurethane giving the highest level of safety.

It doesn’t go deep into the wood like paint and different wood finishes do. However, it leaves a clear coat on the surface of the wood. 

The stronger your coat is and the better the safety, the more thick layers you put on. 

Although polyurethane has a few flaws, don’t rule it out. 

The item gives your wooden floors and furniture multiple kinds of security that will make them last longer. 

For example, a waterproof polyurethane varnish keeps mold and fungi away from my tables, ceilings, and wood walls. 

It can also stand up to heat and light, so it does an amazing job of keeping wood from dying and changing color.

What Happens If Polyurethane Gets Wet?

So, what will happen if you get water on wood that has polyurethane on it? 

Two main things can affect how things turn out:

• How much water does the polyurethane have on it?
• When did the moisture start to settle on the polyurethane?

If I spill something small, like a glass of water, and clean it up quickly, it won’t hurt the polyurethane. 

Since polyurethane is so wonderful at keeping water away, it’s a great example of how it’s carrying out its job. 

It’s made to keep tiny amounts of water from getting to your wood surface.

On the flip side, let’s imagine a pipe broke and my hardwood floors got soaked. If this much water sits on the polyurethane over a long time, the coating will be weakened.

The water will pass through the polyurethane and seep into the wood, making it grow, warp, or possibly even rot as time passes. 

Even when you put several layers of polyurethane on wood, it’s not created to make wood waterproof.

Water can wear down water-based polyurethane more quickly than oil-based polyurethane, so I suggest that you keep that in mind when picking what kind to put on your wood surfaces.

How Many Coats of Polyurethane Does It Take to Waterproof Wood?

Although it won’t fully keep water out of wood, I recommend that you put three to four coats on any surface you’d like to make water-resistant.

This is a useful measure of thumb when using oil- and water-based polyurethanes. 

When you only add one layer, your project won’t be very water-resistant.

Supplies You Will Need To Make Wood Waterproof

• Sandpaper
• Lint-Free Cloth or a Damp Rag
• Sealant
• Paintbrush
• Polyurethane
• Spray or Roller
• Razor
• Water
• Wood Polish 

Grab the above supplies from a quality manufacturer and get ready to waterproof your loving woodwork.

How to Make Wood Waterproof?

Do you know how to make wood waterproof? Learning how to waterproof plywood surfaces blocks water and other things. 

Polyurethane cannot entirely guard wood from water, so I recommend using different mixes and steps.

Here’s the procedure for making wood waterproof using polyurethane,

1. Get the Surface Ready
2. Take the Dust Off 
3. Put Sealant on the Wood
4. Put on the First Coat of Polyurethane
5. Remove the Bumps
6. Wet-Sanding Your First Polyurethane Coat
7. Put on the Second Layer
8. Add the Last Coat
9. Polish the Surface of the Wood

Let me explain my method of making wood waterproof using polyurethane in more detail.

1. Get the Surface Ready

You must use sandpaper, to sand the outside of the wood to make the sealant stick better, get rid of flaws, and prevent air bubbles.

2. Take the Dust Off 

Then normally remove dust with a lint-free cloth or damp rag, and make sure the area is fully dry before going on.

3. Put Sealant on the Wood

Using a paintbrush, you should add the sealant in long, even strokes, smoothing any leftovers with the brush.

Apply a thin and even coat of polyurethane along the direction of the wood grain to avoid polyurethane mistakes.

4. Put on the First Coat of Polyurethane 

I recommend using a good-quality brush, spray, or roller to apply the first layer of polyurethane evenly.

5. Remove the Bumps

After drying, you need to check for drips and use a razor to get rid of any you see.

6. Wet-Sanding Your First Polyurethane Coat

Let the first coat of polyurethane dry for some time and then use wet sandpaper to sand it in a circle.

7. Put on the Second Layer

Put the second coat after the first one is dry, you must wait the amount of time advised by the surface type.

8. Add the Last Coat 

If more coats are needed, make sure each one is fully dry before adding the next one, and I suggest that you follow its instructions for drying times.

Read to know more about, How Many Coats of Polyurethane do you need!

9. Polish the Surface of the Wood

After the wood has dried for at least 48 hours, you need to apply wood polish.

After applying the polyurethane finish, don’t forget to Clean Polyurethane Brush.

Oil-based polyurethane for Waterproofing Wood

Although not waterproof, oil-based polyurethane is more water-resistant. The strength and pleasant finish make it ideal for hardwood floors. 

But in my experience, it takes longer for it to dry between coats, needs mineral spirits for cleanup, is flammable, and smells bad while curing. 

I advise you to protect yourself and work in a well-ventilated place when applying oil-based polyurethane.

Water-based polyurethane for Waterproofing Wood

Surface choices improve water resistance in water-based polyurethane, which is not waterproof. 

In my experience, it’s safer, easy to clean, and dries clear to keep wood color than oil-based polyurethane.

Water-based poly is used for thin, transparent woodworking protective layers as it dries faster and is removed easily with soap and water. 

Cheaper water-based polyurethane can need more uses because of its thinner design, so I recommend you pick higher-quality choices.

How to Protect Wood from Water

Did you know there are other ways to protect your wood from water? If you want waterproof wood, here are other ways you can do it without using polyurethane.

1. Apply Sealant

Sealants make wood watertight for ultimate safety. Sealants stop water absorption by staying on top of wood. I suggest that you put an epoxy sealant since it can prevent your wood from rotting and falling apart. 

Let me show you how to apply sealant to wood. This is what you need to apply sealant on to the wood:

• Stick or Paint Stirrer 
• Sealant 
• Paint Brush or Roller
• Sandpaper
• Lint-Free Cloth or a Damp Rag

Here’s how to waterproof wood with sealant,

1. Mix the Sealant Carefully
2. Use the Sealant Evenly
3. Dry the Coat
4. Sand the Dry Exterior
5. Clean Up the Dust
6. Repeat until Three Coats

I’ll explain these steps about how to apply sealant onto wood in more detail.

1. Mix the Sealant Carefully

Before applying sealant, you must mix it with a stick or paint stirrer.

2. Use the Sealant Evenly

I normally use a paintbrush or roller to apply the sealant to the wood.

3. Dry the Coat

You should use the manufacturer’s given drying time to dry the sealant coat.

4. Sand the Dry Exterior

I recommend that you smooth the dry sealant on the wood surface with sandpaper before putting on the next coat.

5. Clean Up the Dust

You need to clean up the sanding dust with a lint-free cloth or moist rag.

6. Repeat until Three Coats

You must repeat steps 2–5 to put on three coats of sealant, drying and sanding each one before adding the next.

2. Apply Wood Oils

Wood oil is an all-natural method to waterproof wood. Tung oil and linseed oil protect and improve wood’s pure beauty. These are simple to apply and protect your wood for many years.

These are the items you’ll need to apply wood oils on to wood:

• Tung Oil or Linseed Oil
• Natural-Haired Paintbrush
• Clean Cloth
• Fine – Grit Sandpaper

Here’s how to waterproof wood with tung oil or linseed oil,

1. Carefully Mix the Oils
2. Apply Oil
3. Let the Oil Get into the Wood
4. Clean the Surface
5. Let the Oil to Dry Completely
6. Sand the Exterior
7. Repeat to Get the Best Coats 

Now I’ll explain these steps about applying wood oils onto wood.

1. Carefully Mix the Oils

You must mix the wood oils before applying.

2. Apply Wood Oil

I always use a natural-haired paintbrush to put a light coating of oil on the cleaned and sanded wood.

3. Let the Oil Get into the Wood

After that, apply oil to dry places after the oil goes into the wood.

4. Clean the Surface

Normally I clean any extra oil with a clean cloth.

5. Let the Oil to Dry Completely

You need to leave the oil to dry fully following the manufacturer’s directions.

6. Sand the Exterior

Smooth the outside I suggest that you use fine-grit sandpaper.

7. Repeat to Get the Best Coats 

You must use the same steps to put on more oil coats.

1. Apply a Stain Sealant Combination

Lastly, a stain-sealant combination can easily protect wood from water. These sealants are like typical sealants but have color to give your work the finish you want. 

In my opinion, if you wish to keep your natural wood’s look, you should use a sealant or wood oil, however, if you need color, use a stain sealant mix. 

Decking and outdoor furniture use stain sealant mixtures since they’re open in many colors.

Here are the things you need to apply a stain sealant combination on wood:

• Stain Sealant combination
• Natural Bristle Paintbrush
• Clean Cloth 
• Fine-Grit Sandpaper

Here’s how to waterproof wood with stain sealant,

1. Lightly Mix Stain and Sealant
2. Apply Stain Sealant
3. Let the Mix to Soak Into the Wood’s Exterior
4. Removing Extra Mix from the Exterior
5. Give Some Time for the Mixture to Dry
6. Sand the Exterior
7. Repeat the Steps

Now let me explain these steps about applying stain sealant combination on wood a bit more.

1. Lightly Mix Stain and Sealant

Be sure to mix the two before applying.

2. Apply Stain Sealant

Put a thin layer of the mix on cleaned and sanded wood with a natural bristle paintbrush.

3. Let the Mix to Soak Into the Wood’s Exterior

Leave it to soak in and reapply to dry spots.

4. Removing Extra Mix from the Exterior

Wipe the leftover mixture with a clean cloth.

5. Give Some Time for the Mixture to Dry

Leave it to dry fully following the manufacturer’s advice

6. Sand the Exterior

Smooth the surface using fine-grit sandpaper

7. Repeat the Steps

Use the same steps to add more stain-sealant layers.

Tips for Protecting Wood from Water

For your next job, hardwood may not be waterproof. 

Here are some of the best tips I know that will help you protect wood from water:

• You should use pressure-treated or water-resistant wood like cedar or redwoods are great for outdoor projects because they resist water damage.
• Use waterproof sealants like polyurethane, varnish, and wood sealers to protect wood from water.
• To stop water damage, you need to check and care for the wood and replace cracks, gaps, and sealants quickly.
• I recommend that you manage your grading and drainage systems to keep water away from timber things and surfaces.
• To prevent rain and moisture, you must place wood above the ground or under a waterproof sheet or roof.

Polyurethane protects wood surfaces nicely and is commonly used in furniture, flooring, and smaller woodworking projects. 

Polyurethane protects wood from spills and stains but isn’t waterproof. I suggest that you use tung oil, linseed oil, or epoxy to waterproof wood.

Congrats folks! Now you know whether Is polyurethane waterproof and how to waterproof wood properly using the right techniques.

So, let’s answer some frequently asked questions

FAQs

Did I cover all you wanted to know about Is Polyurethane Waterproof

In this article, I’ve deeply discussed whether is polyurethane waterproof and how to waterproof wood using different methods. Plus, I’ve included some tips to make your project succeed as well.

Polyurethane is not entirely waterproof, but it is highly water-resistant. It can effectively repel water in various applications, offering protection against moisture and water-related damage to a substantial degree.

Furthermore, I’ve answered some frequently asked questions a swell.

Hope you’ve learned everything you wanted to know about whether is polyurethane waterproof and how to protect your wood from water element.

If you’re interested to learn more about your wood from outdoor elements, read this, Best Methods to Protect Outdoor Wood Furniture.

Now it’s time to waterproof your loved furniture with the method that suits you the most. Keep practicing until you become a pro at wood finishing!

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