Is Pressure Treated Wood Waterproof Or Needs Sealing?

Is pressure-treated wood waterproof or water-resistant?

We all know that Pressure-treated lumber is made by soaking the boards in preservative chemicals under high pressure which gives it some water-resistant properties.

However, this doesn’t mean you should leave your treated lumber out in harsh weather conditions for too long without protection from the elements.

This article will explain how to waterproof treated lumber in order to stay dry in all weather conditions!

Let’s dive in;

Is Pressure Treated Wood Waterproof?

No, pressure-treated wood isn’t waterproof. The chemical preservatives present in the wood can’t protect it from decay. That means pressure-treated wood can rot over time due to moisture absorption. However, you can waterproof and seal pressure-treated wood to protect it against water damage. 

Should You Waterproof Pressure Treated Wood? 

Yes, you should waterproof any pressure-treated wood to last longer. The chemicals in pressure-treated wood will protect your woodwork from rot and insect attacks. However, these chemicals won’t stop PT wood from absorbing water.

That said, there’s no harm for you to waterproof or seal a pressure-treated wood. Treat it by staining pressure-treated wood, sealing, or using a formula that combines the two.

If you love staining, you can get the best deck stains for pressure treated wood within no time.

Using polyurethane resins will make your wood waterproof and resistant to damages. 

Furthermore, treated wood will last longer than unsealed wood.

The procedure starts with a thorough cleaning of the surface, which is then followed by sanding. The sanding should be rigorous if the wood has a previous finish. Sanding helps to edge the surface, so it’s easy for the stain, seal, or formula to stick.

How to Waterproof Pressure Treated Wood?

The fact that pressure-treated lumber isn’t waterproof doesn’t mean you can’t use it for exterior projects. 

Here are a few wood waterproof treatment options to try;

Combined sealer and staining method 

Combine the two for an enhanced look and protection against moisture and water. 

Wood sealing

Use a coating of lacquer thinner, polyurethane (choose from high-gloss shine to a soft sheen), or varnish. Most people tend to use Lacquer. However, this waterproof treatment for wood can develop yellow pigments with time, thus giving coloration to lighter woods. Deep-toned wood always works best.

Use of tung oil or linseed oil 

Use any of the two for an attractive, protective hand-rubbed finish.

Each method depends on several factors, such as the type of grain and the external conditions.

Materials and tools

  • Linseed oil
  • Tung oil
  • Wood varnish
  • Mineral spirits
  • Deck stain and deck sealers
  • Polyurethane finish
  • Water (optional)
  • Vacuum cleaner or Rags/Cotton Clothing
  • Natural bristle paintbrush
  • Lacquer
  • Fine-grit sandpaper

Methods Of Waterproofing Pressure Treated Wood

Use these three techniques to ensure your wood isn’t only resistant to insect infestation but also waterproof. 

Method One: Using Sealants

Lacquer, varnish, and polyurethane have great properties that make them excellent for proofing your wood against the penetration of water. 

Step 1: Prepare the Surface

Use a clean rag dampened in water or a vacuum cleaner to clean the surface. This is so you can remove any dust or dirt, impurities. 

Step 2: Apply The First Coat

Apply the first layer of the polyurethane finish. After it’s dry, sand it. Then, you can spray or brush the polyurethane on the adequately prepared wood surface.

If you’re using water-based polyurethane, allow at least six hours for the treated wood to dry completely. As for the oil-based polyurethane, wait for 24 hours. 

Step 3: Allow The Coat To Cure

After drying, allow the wood 30 days to cure. 

Expert Tips: 

  • Apply polyurethane at room temperature for impressive results. 
  • Don’t shake the finish before and even after applying it to avoid bubbles on the wood’s surface after the sealer dries up. 
  • Always work in a properly ventilated space.
  • Use polyurethane instead of other finishes because the finish doesn’t yellow quickly. 
  • Poly is best when used on light-toned woods.
  • Use mineral spirits or turpentine to clean brushes used on the oil-based finish, then soap and water for brushes used on water-based poly.

What’s The Composition Of Varnish Sealants?

Varnish sealants are a combination of drying oil, solvent, and resin. 

When used, the finished product will have a hard shell finish that can resist scratches and damages. As a result, it won’t turn yellow quickly when exposed to adverse environmental conditions.

Marine varnish is the best for waterproofing exterior surfaces. It protects against intense damage by the sun, thanks to its UV absorbers.

To seal interior furniture such as coffee tables, Spar Varnish will produce outstanding results. It helps avoid the pesky “cup ring” marks that make your table surfaces look horrible and dirty.

On the other hand, Lacquer comprises synthetic resin dissolved in alcohol and tree resin. It does a perfect job for any wood furniture, apart from lighter woods, as they may start to yellow with time.

See Also: Can you use pressure treated wood for indoor furniture?

Method Two: Warm And Hand-Rubbed Oil Finish

Linseed oil is created from seeds of the linseed–flax plant. It protects dark-grained surfaces (e.g., mahogany and walnut timber) against environmental elements. Tung oil is extracted from tung trees.

Here’s the procedure for waterproofing treated lumber with hand-rubbed finishes:

Step 1: Prepare The Wood Surface

Clean off the dust on the wood surface using a rag or a vacuum cleaner. 

Also, work in a properly ventilated environment because some poly contains highly volatile organic compounds.

Step 2: Prepare The Formula

Stir the formula correctly. Use a natural bristle brush to apply the formula to your pressure-treated wood. Allow the oil to soak. 

Step 3: Wipe Off Excess Oil

Wipe off residual oil with a clean rag and before the wood dries. 

Step 4: Light Sand The Surface

Use fine-grit sandpaper to lightly sand on the surface of the wood. 

Step 5: Apply The Last Coat

Apply the second coat to your wood’s surface and let it dry completely. Add more coats until you get the desired finish.

Method Three: Two In One Sealer And Stain Approach

If you want your pressure-treated lumber to have both sealer and stain, this is the best method. The two don’t have to be applied separately, thus saving you time and money. 

The finish comes with color pigments that contain extra binders. The implication is, your final product will either be transparent, opaque, or semi-transparent, depending on the concentration of your formula.

If used on exterior structures, refinish them after every one year, so your wood remains attractive.  

Unlike Alkyd-based stain-sealers, stain-sealants formulas soak in the wood to allow for excess evaporate. Alkyd-based products will leave a light surface coating, making them suitable for interior wooden structures.

What’s The Lifespan Of A Pressure Treated Lumber?

How long will pressure treated wood last in concrete?

The lifespan of pressure-treated wood is 40 years. However, it would help give your wood proper care by using preservative chemicals that soak it into the wood fibers to prevent rot, particularly on exterior structures and surfaces such as decks. 

The procedure for the treatment of this wood involves putting the wood in a retort, a cylindrical chamber with one door at one end. Waterborne chemicals are infused into the lumber under pressure for the pressure-treating process. 

Is Pressure Treated Wood Water Resistant?

No, pressure-treated wood is not water-resistant nor does it have a waterproof surface. After pressure or chemical treatment, the wood becomes durable and resistant to splitting and fungal decay. For complete water resistance, seal the wood using a penetrating oil or semi-transparent stain.

In climates where there is high humidity, condensation, or ongoing exposure to ground moisture, waterproof treated lumber with a non-emulsified waterproofing compound.

Does Pressure-Treated Wood Need To Be Sealed?

Yes, pressure-treated wood needs to be sealed at least every year. That will enable the wood to provide protection against moisture continuously and enable your wood to maintain a great look throughout. 

However, you should also consult with the seller as pressure-treated wood of premium quality comes with built-in sealers. Such would last for several years without maintenance. 


What Happens If Pressure Treated Wood Gets Wet?

When the wood gets wet, it becomes softer, making it easy to rot. The recommended moisture content is below 15%, especially for kiln-dried wood. However, for pressure-treated wood, the moisture content shouldn’t exceed 17%. To avoid rotting, waterproof your wood before using them for exterior projects. 

Can Pressure Treated Wood Get Rained On?

Yes, pressure-treated wood can get rained on. Unfortunately, at this point, the wood doesn’t have any protection that can enable it to withstand the effects of rain. Consequently, the wood will start rotting. 

How Long Will Pressure Treated Lumber Last Underwater?

Pressure-treated wood can last for 20 years underwater. It can’t be affected by processes such as electromagnetic reactions or corrosion. 

How Long Do You Have To Wait To Waterproof Treated Wood?

After the pressure-treating process, you should wait 30 days for the chemical preservatives to infuse the wood properly.

The danger of rushing is that the sealant may not soak, and the quality of your project will be compromised. 

Use the sprinkler test to check if the wood is ready to be waterproofed. 

The test involves sprinkling a few drops of water on the wood then observing the behavior. If the drops get absorbed immediately, the wood is dry and ready for staining. However, if they form bubbles, the wood isn’t yet dry. 

Can You Burn Pressure Treated Wood?

Burning treated wood is not recommended because it can release harmful chemicals and toxins into the air. Treated wood may contain preservatives or chemicals that protect it from decay and insects.

When burned, these substances can pose health risks to humans and the environment. Always use untreated, properly seasoned wood for safe and clean wood burning.

What Is The Best Sealant For Pressure Treated Wood?

My recommendation for the best deck sealer for pressure-treated wood is Ready Seal 520 Exterior Stain and Sealer for Wood.

With Ready Seal 520, you don’t need a primer before sealing. And it reaches its true color in 14 days.

Say goodbye to back brushing and surface runs, streaks, or laps. Finally, it’s touted as the best waterproofing for pressure-treated wood because doesn’t require thinning nor diluting during application.

Is It Better To Stain Or Paint Pressure Treated Wood?

Staining is better because of the following reasons:

  • Painting treated lumber involves numerous procedures that make it a bit more complicated. If you don’t get all the steps right, you’ll end up with poorly painted wood. 
  • Staining is more durable and stable than the paint, which will begin to peel off with time. 

See: Best waterproof wood paint

Why Use Of Stain And Sealant Combination

Using stain and sealant combination can have your wood protected from being damaged by moisture. This formula is a dual-purpose waterproofing agent as it helps seal the wood surface and also stains it. It is good to use stain sealant products because most of them have extra binders that are either oil or water-based.

See: How long should you wait to stain pressure treated wood

Can You Clear Coat Waterproof Pressure Treated Wood?

Yes, you can clear coat any pressure-treated wood even though it is already protected against termite attack and decay. However, you should apply the water-repellent sealer to exposed wood surfaces immediately after you’re done with the construction. Go for treated Southern Pine lumber as it will accept a finish well similar to untreated material.

Is pressure treated wood weather resistant

Even though pressure-treated lumber keeps bugs away and prevents decay, it is not weather resistant. Moisture may enter through the pores and cause the wood to swell. As the treated wood sun-dries, it will shrink. Over time, the wood will split, splinter, or even bend as a result of this constant swelling and shrinking cycle.

Can you polyurethane pressure treated wood

Yes, you can seal treated wood with polyurethane to protect it from elements such as rain and harsh UV rays. A minimum of 2 coats of polyurethane on your pressured treated wood is good enough. Allow ample drying time between coats of polyurethane for a great finish.

Learn More: What does treated wood look like

Is treated wood waterproof?

So, is pressure-treated wood water-resistant or waterproof?

As you’ve seen, you shouldn’t shy away from using pressure-treated wood because it’s not waterproof. When you waterproof treated wood, you’re combining forces; waterproofing and insect infestation resistance. After that, you can even use it for your exterior constructions without freaking out that the rain or moisture will mess things up. 

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