If you have a deck, stairs, or other structure made with pressure treated lumber, you may not like the look of the brown or green wood surface created by pressure treatment. You may be asking, can you paint pressure treated wood?
The short answer is, yes, but it’s a little more complicated than painting wood that isn’t pressure treated. There are a couple of things you need to know about how to prepare the wood before you get out the paint and paint brush. You also need to use the right kind of paint to make this project successful.
What Exactly is Pressure Treated Wood?
Pressure treating wood is a process done at the lumber mill to make the wood more resistant to rot and fungus attack. When lumber is processed, it is submerged in a vat of chemicals and put under high pressure to get the chemicals to penetrate deeply into the wood grain. After that, the wood is set on racks until it is dry to the touch and ready for sale.
There are several different chemicals used for treating lumber. The most common are chromated copper arsenate, or CCA and alkaline copper quaternary, or ACQ. However, building departments are phasing out CCA wood for residential use, so you are more likely to find it on existing structures.
The copper is what often gives pressure treated wood a slightly green tint, although the ACQ treatment makes the final product come out a brown color.
If you look closely at the surface of pressure treated lumber, you will notice small indentations spaced over the board. These help the chemicals penetrate better into the surface of the wood, and their presence is a sure way of determining a piece of wood has been pressure treated, no matter what the color is.
The chemicals used for pressure treating lumber are toxic if you ingest or inhale them. Always use gloves when handling this type of wood, wash your hands after handling it, even when you use gloves, and use a dust mask when you saw or drill holes in pressure treated lumber.
Here are the steps to paint your lumber
1. Dry the Lumber
Unless you use kiln-dried pressure treated wood, one problem with putting a coat of paint on this type of wood is that pressure treated lumber is not thoroughly dry for quite a long time after the chemical pressure treatment. Expect to wait three to four months for new pressure treated wood to completely cure before painting it.
While you can handle new pressure treated boards without noticing the chemicals on your gloves, there is still moisture, pitch, and resin inside the wood which needs time to dry out before you paint it.
Because it is not thoroughly dry, new pressure treated lumber can quickly warp and bend if you don’t handle it correctly. After you buy new pressure treated lumber, build with it right away, or keep it stacked flat in a dry place and wait at least 60 days to four months before painting it. Patience is a crucial ingredient in this project.
If you’re not building right away, prevent the boards from warping by stacking them using stickers – thin pieces of wood slightly wider than the wood you are stacking.
Place the stickers under the bottom piece of wood on the ground at each end of the board and spaced about every four feet under the length of the plank. Then set down your first piece of wood on the bottom stickers.
Then put stickers on top of the bottom board, using similar spacing as before, and stack the next piece of lumber on top. The stickers provide air space between the planks and help with drying and keeping the wood flat and straight until you’re ready to use it.
Besides making sure your pressure treated lumber is dried out from the treatment process, it’s also essential not to paint any wood if it’s wet from rain or snow.
How can you tell if the chemicals are fully dried out before painting pressure treated wood? There’s a simple test you can use.
Just pour a small amount of water onto the wood and watch what happens. If the water beads up on the surface, the wood is not dried out enough. If the water sinks into the wood grain, it’s dry enough to get out your paint brushes.
Kiln-drying involves stacking lumber in a container and applying heat to help it dry faster. Kiln-dried lumber does not warp as easily as wet lumber because all of the moisture evaporates during the drying process.
You can buy kiln-dried pressure treated lumber, also called Kiln-Dried After Treatment, or KDAT, if you don’t want to wait as long for the wood to dry before you paint it.
2. Clean the Wood
If you are painting a pressure treated structure outdoors, the wood may have dirt and grime on it which you need to remove before painting. Also, you need to wash off the chemicals on the surface of the wood before you paint.
Doing this is simple. Just use a stiff brush, a bucket of warm water with a splash of mild detergent, and a hose with a jet nozzle. Wet the area, scrub with the brush and soapy water, and use the spray of water to clean it off. Don’t use a pressure washer because this can gouge the wood, reducing the effectiveness of the pressure treatment for preventing rot and insect damage.
After cleaning, you’ll need to wait for the wood to dry completely before moving on to the next step.
3. Prime It Thoroughly
For your final paint job to completely cover the color of the pressure treatment, it is essential to use a high-quality primer before you paint on the finish coats. Be sure the label on the primer says you can use it outside. Using a primer will also ensure the finish coats of paint adhere to the wood surface without peeling.
Apply a coat of primer to all surfaces of the wood you plan to paint, and let it dry for at least one day before moving on to the next step.
You can use a paint sprayer or a paintbrush to apply both the primer and finish coats, but paint rollers probably won’t get paint into all of the crevices on the surface of most pressure treated wood.
4. Top Paint Coats
The best paint to use for pressure treated wood is a high-quality, exterior acrylic latex paint. If you are installing lumbers in an indoor location, you can use interior paint. Avoid oil-based paints for both the primer and finish coats.
You can choose any color you like, but lighter colors may take more coats to hide the green or brown color underneath completely unless you use a primer. Whatever color you use, plan on doing at least two finish coats over the primer, and wait a day between coats so the paint can dry thoroughly.
It does take a bit more work and patience to paint pressure treated wood than painting untreated lumber. However, if you follow these steps carefully, your finished job will likely come out looking good and lasting a long time.