Pressure treated wood can have knots, nicks, or blemishes that can make decks, fences, and other surfaces less attractive. Sealing or staining doesn’t mask damage or marks, so can you paint pressure treated wood?
You can paint pressure treated lumber once it dries, which is a matter of patience. The wood needs to dry so the paint will adhere properly, which can take weeks or months depending on the season and climate. Once dry, wash the surface, let dry, and apply a quality primer, followed by two coats of paint.
In this article, we’ll explain what pressure treated wood is and whether it can or should be painted. We’ll discuss how long you have to wait to paint it and why, and what happens if you don’t wait for the lumber to dry. We also provide reviews for the best primer and paint to use. By the end of the article, you’ll understand how to paint pressure treated wood.
What Is Pressure Treated Wood?
Cedar, cypress, and redwood have a natural preservative that protects them from insects, moisture, and rot. Pine, spruce, and fir do not have natural preservatives to repel insects and moisture or prevents rot. To protect them from rot and insect damage when used outdoors they are pressure treated.
Pressure treatment is a process that places wood into a chamber or tank which is depressurized to remove air. Pressure is then used to replace the air with chemical preservatives, and then the excess chemical is ‘vacuumed’ off and reused. The preservatives make the wood more durable and resistant to insects, moisture, and rot. The solution can prevent internal decay for 40 years or more but does not stop discoloring or weathering.
The chemicals are infused a short way into the surface of the wood to form a protective shell. It doesn’t go all the way through. The deeper the chemical penetrates the wood and the amount that stays in the wood, improves the protection. Incising is a process that puts small slits into plank surfaces for deeper and thus greater penetration.
There are water-based, oil-based, and creosote preservatives. Water-based include Chromated copper arsenic (CCA), alkaline copper quaternary (ACQ), ammoniacal copper zinc arsenate (ACZA), copper azole (CA), and micronized copper azole (MCA). Most water-based preservatives are used for residential, industrial, and commercial applications. Creosotes are commonly used for docks, guardrails, bridges, and railway ties. Oil-based infusions protect utility poles, pools, and crossing arms.
Types of Pressure Treated Wood
There are three types of pressure treated wood: Above Ground, Ground or Ground Contact, and Heavy Duty or Heavy Duty Ground Contact. It is important to use the correct type of wood based on the application or end-use.
Above Ground
Wood used for outdoor applications that do not touch the ground, dry out when no precipitation, and aren’t in tropical climates contains less chemical preservatives. Use for outdoor furniture, decks, lattice, spindles, railings, and stairs. The boards can also be used for fences that have good airflow under and around the wood, and do not contact the ground or have vegetation or debris piled against it.
Ground or Ground Contact
Lumber that contacts the ground or is in the ground often contains double the amount of preservative as above ground. It is used for projects within 6-inches of the ground that are exposed to moisture or dampness from vegetation, debris, or sprinklers. Ideal for deck posts, beams, or joists, stringers, planter boxes, and retaining walls.
Heavy Duty or Heavy Duty Ground Contact
Heavy-duty timbers usually contain triple the amount of preservative compared to above ground lumber. It is used to support structures from barns, sheds, and even homes. It is often used for skids and cribs, or sunk into the ground, concrete, or freshwater as supports. It can even withstand saltwater splash.
Can You Paint Pressure Treated Wood?
Pressure treated lumber is protected from rot and insects but not from graying or weathering. The chemical solution that is infused into the wood leaves it wet or damp. New planks often ooze as screws bite in and squeeze the moisture out of the cells. Painting wood when it is wet is a waste of time as it won’t bond with the wood, and will peel.
Pressure treated wood must be dry before it can be painted, stained, or sealed, which can take weeks if kiln dried after treatment or months if not. Sprinkle water on the surface, if it beads don’t paint, if it absorbs, it’s paint ready.
If you’re planning to paint pressure treated lumber once it’s installed, purchase kiln-dried material. On the bar-code label look for KDAT (kiln-dried after treatment) or ask the service people at your lumberyard. The wood has less moisture content, so will dry more quickly and evenly. Waiting for some planks to dry due to high moisture content is frustrating.
You may have pressure treated lumber on existing structures that have weathered or no longer looks good stained. Wood that has been outdoors for one or more years can be painted if it is surface dry. If it has been previously sealed or stained it may need to be stripped and cleaned before paint is applied.
Painting treated lumber offers some advantages over painted untreated lumber in exterior settings. However, chemically preserved lumber has only been in use for about 80 years. Paint has been used on untreated lumber successfully for centuries.
Applying paint offers a greater choice of colors than stains for the wood. The opaque film will hide blemishes and discoloration, protects the wood from the elements, and may blend better with other structures and landscaping.
Should You Paint Pressure Treated Wood?
Painting pressure treated lumber is a point of argument. Some professionals who argue that you should never paint treated wood and others who argue that it is fine and explain when and why you should paint it. They even provide instructions for successfully applying paint to treated material. To add to the confusion, there are even those who question using treated lumber at all if it’s vertical and going to be painted.
Painting lumber is a matter of choice and depends on where the wood is being used and its condition. There is however a consensus by all parties that the lumber must be dry, which can take days, weeks, or months depending on the type of lumber and the climate. Using untreated material or kiln-dried after treatment (KDAT) will accelerate drying, but can still add time to the project completion date.
Those who are against painting treated lumber often point out that the purpose of infusing wood with chemicals is to protect it from the elements. So, why paint it. They argue that the paint will prevent the wood from breathing and cause mold, mildew, and rot.
Additionally, treated lumber expands and contracts as it gets wet, which will cause the paint film to split and crack; necessitating scraping and cleaning more frequently. Another concern they have is that paint makes horizontal wood surfaces slippery, and a potential slip hazard.
Painting exterior untreated wood has been done for centuries and the quality of water and oil-based exterior paint has significantly improved over the years. If you choose to use untreated wood for vertical and even horizontal surfaces of houses, sheds, and other structures you’re following common practice.
Make sure the wood is dry, use a good quality primer and paint that will sink in and protect the wood. The better penetration, the longer it will be before the surfaces need to be repainted, and the longer the wood will last.
Painting pressure treated surfaces requires the wood to be dry which can take up to six months or more. Splash some water on the wood, if it is absorbed, the wood is ready to paint, if it beads up on the surface, it isn’t ready. Painting treated wood that is dry will protect the outer surface from moisture damage, mold, and mildew. The paint will hide knots and other surface blemishes, and provide a unified color.
Whether painted or not, pressure treated lumber will rot if the surfaces are unable to dry, similar to untreated wood. Painting cured wood won’t adversely affect the wood lifespan, and usually extends it, similar to untreated material.
Pros
- Protects the surface from mold, mildew, and rot
- Protects from the elements and UV rays
- Hides knots and blemishes
- Extends the life of the wood
- Creates a uniform color
Cons
- Takes time to dry
- Can seal in moisture and cause rot
- More expense in materials, labor, and time
- Makes horizontal surfaces slippery
How Long Before You Can Paint Pressure Treated Wood?
Painting pressure treated wood is a matter of patience. The wood must be dry or cured before it is painted, which can take weeks or months. The water used in the chemical infusion needs to evaporate out of the wood, so that paint can absorb and bond to the wood.
Using treated wood that was kiln dried after infusion will allow for painting within several weeks as the moisture content is more uniform and between 6% and 8%. Test the surface for dryness with a light splash of water. If the water is absorbed, then it will absorb paint or stain.
Treated wood that didn’t go into the kiln can have moisture readings above 15% and take up to six months to cure depending on climate and location. Additionally, wood from different lots can have different drying times too, which can have some boards dry sooner than others. It is best to check random boards with the splash test if unsure if they came from the same lot.
What Is the Best Paint and Primer to Use for Pressure-Treated Lumber?
The chemical bath that infuses chemicals into wood is water-based. Using a quality water-based primer and a premium 100% acrylic paint improves adhesion and will withstand the expansion and shrinkage of seasoned lumber. Here are our recommendations for the best primer and paint.
KILZ Premium Primer/Sealer
KILZ Premium Primer/Sealer is made in the USA water-based primer that can be used indoors or out on a variety of surfaces, including pressure treated lumber. It fills in small imperfections, hides stains and discolorations, and seals surfaces for a smooth, uniform finish. It contains a mildewcide to prevent mold and mildew but produces low odor and almost no VOCs.
KILZ is ideal for areas prone to high humidity. It provides excellent adhesion on clean wood or oil or latex painted surfaces and can be used under both too. Use soap and water to clean brushes, rollers, and other tools or spills. A gallon will cover between 300 and 400 square feet.
Rust-Oleum 1992502 Painters Touch Latex
Rust-Oleum Painters Touch is a premium water-based 100% acrylic paint that provides a durable, smooth finish for pressure treated wood and other surfaces. Used on properly prepared surfaces inside or out, the paint is chip and fade resistant and quick-drying. Three thin coats will cover better than two thick coats.
Rust-Oleum is available in a variety of colors with flat or semi-gloss sheens and covers up to 400 square feet per gallon. Apply thin coats of paint with a synthetic brush, a roller isn’t recommended, and wait for 2 to 4 hours before spreading the second coat. A third thin coat may be required. Clean brushes and tools with soap and water immediately.
Painting Pressure Treated Wood: Step by Step
There are many reasons to paint pressure treated wood. It may have weathered and turned gray over the years, you don’t like the blotchy color, or you want to protect it from weathering. You may also have a specific color scheme to blend with other buildings or landscapes.
New wood that is kiln dried after treatment has 6% to 8% moisture content and will dry more quickly than preserved wood that skips the kiln. Wood that has turned gray with age or was installed six months or 20 years ago is probably ready to paint. Do not paint newly installed pressure treated lumber unless it absorbs water during the splash test.
If you have to replace damaged planks you’ll need to let them cure before painting. I tend to have half a dozen spare planks in my wood rack just for such a need. That means I can paint and replace all at once without waiting. Alternatively, purchase what you’ll require and let them dry over the offseason so they’ll be ready when the next season starts.
Before You Start
Check the moisture content of the wood. Use the splash test to make sure the wood is dry and will absorb the paint. If the wood beads water in the splash test, cover it with a tarp but allow wind and air to still flow around it. The tarp will increase evaporation and prevent outside moisture from keeping it wet.
Ensure all nails and screws are set properly, repair or replace damaged wood, remove items from the surface, and sweep to remove loose dirt. Collect tools and supplies required to complete the task, including cleaning supplies, primer, paint, brushes, and possibly a paint sprayer. You may also wish to cover bordering plants or surfaces with plastic and tape to prevent paint splatter.
Clean the Wood
If the wood was sealed or stained previously, you may need to use a stripper before washing the surface. If you are painting a surface that was painted in the past, it may require some scrapping or wire brushing to remove any loose paint. New or old wood should be cleaned to remove dirt, oils, and any surface residue. Rust-Oleum Wood Cleaner and Coating Prep is a good product for getting surfaces ready to paint.
Use a bucket with dish soap and water and a stiff bristle brush to wash the surface, and rinse with clean water. If there is mold or mildew present, use a cleaner with a mildewcide, and rinse well. Let the wood dry thoroughly before applying primer or paint. Stripping or cleaning the wood may leave it feeling furry due to surface grain lifting. Use 60 to 80 grit sandpaper and lightly scuff the surface, and then sweep, vacuum, or use a tack cloth to remove any sanding dust. Wear a dust mask or
Apply Exterior Primer
Once the pressure treated wood is clean and dry it’s safe to apply primer. Use a premium exterior primer suitable for pressure treated wood. I recommend water-based KILZ Premium Primer-Sealer. Apply with a brush going with the grain. Although a sprayer may be quicker, it doesn’t cover as evenly. You can opt for the sprayer if there is detailed or ornate wood to paint.
A quality exterior primer penetrates the pores and bonds to the wood. It hides blemishes, seals the surface, and prevents moisture from entering the wood, or tannin and sap from bleeding through. Primer creates a uniform and slightly coarse surface so the paint will adhere more effectively whether the wood is 6 months or 20 years old.
Paint the Wood
Allow the primer to dry before painting, usually 4 to 24 hours depending on climate. Use a water-based 100% acrylic premium paint for the best results. We suggest using Rust-Oleum 1992502 Painters Touch Latex in the color of choice.
Expect to apply two or three thin coats instead of one thick layer. Only paint when the temperature is within the acceptable range (50°F to 85°F), and follow the manufacturer’s instructions. The paint will dry better on warm days with low humidity.
Many professionals suggest beginning painting in the morning so there are more hours of daylight to complete the task, and natural light is better. Apply thin coats of paint with a brush. Use even strokes and ensure the surface is fully covered.
Let the first coat dry before spreading the second layer of paint. Apply a third coat only if necessary to firm up the color.
Paint, like sealer and stain, will last longer on surfaces that are vertical such as walls, railings, and fences than on horizontal surfaces like decks and floors. It should also be noted that stain and sealers need to be reapplied periodically too, so don’t reduce maintenance over paint.
What Happens If You Paint Pressure Treated Wood Too Soon?
The chemical bath that infuses wood with preservatives and protects against mold, mildew, insects and rot leaves the wood very wet and heavy. Even kiln-dried wood contains excess moisture that needs to evaporate. For paint, stain,or sealer to properly absorb and bond with the wood, it must be dry.
Painting pressure treated wood when wet won’t produce good adhesion. The paint will blister, crack, flake or peel, often within a year or less. Additionally, sealing one surface of the wood forces moisture out the other faces, and can cause the wood to warp or twist due to unequal drying.
If the wood is wet, neither water nor oil-based paint will bond well with the wood. Oil and water don’t mix, so the excess water in the wood will reject the oil. Much the same occurs with water-based paint if the surface isn’t dry.
Wood that is treated but not kiln dried ranges from 35% to 75% moisture content and can take well over six months to cure. Kiln-dried treated lumber is often between 6% and 8% moisture content but can be as high as 19% and take months to dry.
A good rule of thumb is to wait six months before painting, staining, or sealing pressure treated wood, and only apply paint after it absorbs moisture from a splash test. A little bit of patience will save you time, energy, and the added expense of fixing a wet-wood paint job.
Conclusion
Painting pressure treated wood provides a uniform finish that hides knots and other blemishes, and protects the wood from UV damage, mold, mildew, and rot. The most difficult part is waiting for the wood to fully dry so the paint absorbs and bonds properly.
I hope you have a better understanding of how to paint pressure treated material, and why the wood to be completely dry. If you found the article interesting, please share it with others who may find it helpful. Your comments and suggestions are always appreciated.