A Complete Guide to Sealing Pressure Treated Wood

Pressure-treated wood is a homeowner’s darling when it comes to outdoor structures like pergolas, fences, and decks since it naturally resists insects and rot.

Although the pressure treatment procedure injects the wood with chemical preservatives that fight decay and insects, it does not provide complete protection from the elements, specifically moisture and UV rays.

That begs the questions; is sealing pressure treated wood required and what’s the best way to do it? Read further for answers to all your questions and recommended products.

Article Contents

Can You Seal Pressure Treated Wood?

The quick response is a definite “yes!” Sealing pressure treated wood adds an extra peace of mind by adding a layer of water-repellent and UV protection.

Failing to seal pressure treated wood properly can result in a multitude of issues. Softwoods, which are common in pressure-treated uses, are prone to a relentless cycle of expansion in moisture and contraction in dryness.

The back-and-forth movement can cause over time unsightly cracks, splinters, and warping that compromise both the look and integrity of your outdoor investment.

Furthermore, even treated wood will discolor and gray from prolonged exposure to the sun. Therefore, applying a proper seal to pressure treated wood is a very crucial step in maintaining its beauty and durability, especially for new deck installations.

What is Pressure-Treated Lumber?

In order to appreciate the significance of pressure treated lumber, it is nice to know what it is. Pressure-treated lumber refers to wood that undergoes a process whereby wood, typically softwoods like pine, is placed in a vacuum-pressure tank.

This chamber forces chemical preservatives into the wood fibers far more effectively than surface applications. Copper azole (CA-C), alkaline copper quaternary (ACQ), and micronized copper azole (MCA/MCQ). According to the American Wood Protection Association (AWPA), these chemicals offer excellent protection from fungal decay and insect attack.

These treatments don’t necessarily waterproof the wood or guard it from the sun’s damaging UV rays, though. This translates to your pressure-treated wood deck being safe from termites but not from moisture absorption, which can lead to a load of issues like cracks and splinters while the wood expands and contracts.

Is Pressure Treated Wood Right for Me?

Pressure-treated wood is a popular choice, however understanding all your options for outdoor projects can be helpful. For a comprehensive overview of a wide variety of decking materials and their pros and cons, explore our guide on selecting your best decking material.

When to Seal Pressure Treated Wood

One of the myths is that you must wait a long period of time before you can seal a new pressure treated deck or project. While a six-month or even one-year wait was once recommended, the way lumber is treated now allows newer pressure-treated lumber, such as those products that have been treated with micronized copper preservatives, to be ready for a seal for pressure treated wood within 30 days of installation. Some kiln-dried after treatment (KDAT) products can be ready even earlier.

The surefire way to determine if you’re ready for sealing pressure treated wood is the “sprinkle test” or “water drop test.” Simply drop a few water drops onto the wood surface at several points. If the water beads up and stays on the surface, the wood contains too much moisture and isn’t yet ready to seal.

If the water simply absorbs into the wood, it is dry enough for a pressure treated lumber sealant. This significant step ensures adhesion and performance of your pressure treated wood sealant of choice.

Local weather and direct sunlight can affect drying times, so always perform this test.

Choosing the Right Sealer for Pressure Treated Lumber

In choosing the right product to seal pressure treated wood, you have several options depending on the desired level of protection and appearance. There are a variety of sealants, stains, and paints on the market, each with its own characteristics.

• Sealants: For those who wish to preserve the wood’s natural color and grain appearance, a clear or semi-transparent water repellent is most appropriate. Look for a pressure treated wood sealer that contains UV stabilizers to combat sun damage and graying. Such penetrating finishes do not form a surface film and, therefore, will not peel or flake.

Where to buy clear or semi-transparent water repellents:

Clear Wood Sealers at The Home Depot

Clear Wood Sealers at Lowe’s

Thompson’s WaterSeal Clear Wood Sealer

• Stains: If you wish to add color but still be able to see the wood grain, a semi-transparent stain is an excellent choice. Most stains also have hybrid versions that combine the oil-based products’ deep penetration and color richness with the ease of cleanup of acrylics. Most importantly, ensure your chosen stain also has a water repellent and a UV stabilizer for total protection of pressure treated wood. An oil-based stain is often recommended because it is long-lasting and has the ability to penetrate the wood fibers.

Where to buy semi-transparent stains:

Semi-Transparent Exterior Stains at The Home Depot

Semi-Transparent Exterior Stains at Lowe’s

Cabot Semi-Transparent Stain + Sealer

• Paints: Painting is also an option for an opaque, solid finish that will completely hide the wood grain. When painting pressure treated wood, start with an alkyd oil-based primer. This primer provides a great bond and will seal in any possible tannin bleed-through from the wood. Finish with two coats of high-quality acrylic latex top coat paint for long-lasting, durable color. Don’t forget to prime cut ends, as these are especially susceptible to moisture uptake.

Where to buy alkyd oil-based primers for exterior wood:

Exterior Oil-Based Primers at Sherwin-Williams

Alkyd Primers at Benjamin Moore (Look for “Alkyd” formulas)

Where to buy acrylic latex paint for exterior wood:

Exterior Latex Paint at The Home Depot

Exterior Acrylic Latex Paint at Lowe’s

Whatever your decision, always look for products that are specifically labeled for treated lumber sealant use and adhere to the manufacturer’s instructions for best performance.

How to Seal Pressure Treated Wood

• Clear the surface
• Test a small area 
• Apply evenly
• Allow adequate drying

Once you’ve selected your product and made sure the wood is ready, applying sealant to pressure treated wood deck or other structures is straightforward:

• Preparation is Key: Before applying any sealer for pressure treated wood, ensure the surface is clear and free of debris. On older decks with heavy grime buildup, a heavy pressure wash (with a low setting to avoid damaging the wood) may be called for, a common step in our deck restoration services. Allow the wood to dry completely after washing, repeating the “sprinkle test” as needed. Protect nearby plants and surfaces with tape or drop cloths.
• Test an Inconspicuous Area: Always apply a small amount of your product of choice to an unseen area first. This allows you to test for good adhesion and ensure you like the appearance before committing to the entire project.
• Apply Evenly: On large areas like a seal pressure treated wood deck, a deck speed mop or paint pad applicator is often faster and provides a more even finish than a brush. These tools hold a good amount of product and allow one to apply smooth, sweeping strokes. Brushes are ideal for cutting in edges, tight areas, and the end grain of boards, which tends to absorb more product. Use a thin, even coat, attempting to eliminate puddles. Usually, one coat of sealant or stain is all that will be necessary.
• Allow Adequate Drying: Most sealers and stains used in treated lumber sealant projects take between 24 and 48 hours to dry. Follow the instructions on the product label. Try to plan your project during a dry spell of weather with no rainfall in the near future to enable the product to cure properly and avoid blotchy finishing. Do not use it in direct, heavy sun or extreme temperatures, which can cause the product to dry too quickly on the surface and not penetrate correctly.

Aftercare for Your Pressure Treated Wood

Sealant or stain application is not a single job. To keep your pressure treated wood deck or any other outdoor structure in its best shape, maintenance at regular intervals is necessary. Your deck should be cleaned at least once a year to get rid of dirt, grime, and algae and mildew growth, which can hold moisture against the wood.

Most clear water repellents and semi-transparent stains are enhanced with reapplication every 1-3 years, depending on sun and weather exposure. By periodically inspecting your treated lumber for fading, water absorption, or minor cracks, you’ll know precisely when to reapply a new coat. By taking this proactive step to waterproof pressure treated wood, you’ll typically match how long a deck should last, for pressure treated wood, this is about 10-20 years.

Final Words

In short, while pressure treatment gives you the underlying protection, you definitely need to seal pressure treated wood for the added benefits. Spending the time and money to invest in the right pressure treated wood sealant and doing the right application and maintenance steps will keep your outdoor structures looking good and lasting for years to come, truly protecting your investment.

Protect Your Investment with Experts

Sidex are siding and decking contractors that also offer professional sealing services, ensuring your pressure-treated wood lasts longer and looks its best.