Any time you use wood or a wood product for an outdoor building or other construction such as a deck, it’s a good idea to use pressure-treated wood. This wood is treated to stand up to the weather elements much better than would untreated wood.
Of course, if you are using the wood for siding for your shed, you probably want to paint it to match your home. Similarly, many people like their decks to match the trim on their homes or perhaps provide an accent color.
The good news is that you certainly can paint most pressure-treated wood. You can also stain it if you prefer. With some woods, you may need special paint, but for most lumber, either oil-based or latex-based paint can be used.
If you are using some rather unusual wood, such as cedar, ask for advice on the kind of paint or stain you need.
Can You Paint Pressure Treated Wood?
It’s good to know a bit about the type and grade of the pressure treated wood your wanting to paint before beginning.
Lumber Grades – Treated lumber comes in varying grades. Sometimes it is graded SS, #1, #2 or #3. Some mills grade it as A, B, C and D. However, it is graded, the grades are usually thought of as being used for the number of defects in the lumber, such as knots and splits. The moisture content of the wood at the time of milling also plays into the rating.
While this is true to some extent, the rating actually denotes the strength of the lumber. The fewer defects the lumber has, the stronger it is, so lumber rated with a stronger rating will naturally be freer of defects.
While the different ratings your lumber may have may get a bit confusing, there should be a stamp that tells you the tree species it came from, the grade, moisture contents, the mill it came from, and the organization that inspected it. If you aren’t sure what you need, the lumber company personnel will be glad to advise you on what to get that’s best for your project. They can also advise you on the best paint to use on the lumber you choose.
While paint will help preserve the wood, even after some of the chemicals used in the pressure treatment have lost some of their effectiveness, there is one other alternative to paint or stain. This is buying pressure-treated wood that is already tinted with color. The tinting is available in natural wood tones such as walnut, redwood and cedar. The tinting actually will protect the wood longer than would painting.
Preparing Pressure Treated Wood for Paint
Wash the wood – You need to wash off any dirt, sawdust or other debris. This will take a while, as it involves actually washing the wood with soap and water. It’s best to use rags and wash the wood by hand. Using a pressure washer will force more moisture into the wood, causing quite a bit more drying time later.
Be careful not to miss any spots. You never know if a piece of lumber brushed up against something oily while being loaded or moved, and you probably won’t notice a small spot until you try to get the paint or primer to adhere. Washing the wood with soap will also help remove some of the treatment chemicals from the surface, allowing your primer to stick properly.
After washing, rinse off the wood, then dry it with clean rags. If you are using enough wood for a shed or large deck, this will seem like a pain, but it’s worth the time and work.
If the wood has been sitting around for a long time, it may need a deeper cleaning. There are commercial cleaners available. You can use a pressure washer with the cleaner and rinse off the wood, but again, this will add to the drying time.
If your lumber has been treated with CCA, or chromate copper arsenate, you may need to treat the surface before attempting to apply any primer or paint. You’ll also need to use all latex-based primer and paint, as the chemicals in the lumber can be affected by any oil-based product.
Dry the wood – Even when you dry the wood with rags, you’ll need to let it air dry. The rags only dry off the outside. You’ll need to make sure the wood is dry all the way through, and this will take time. In fact, if the lumber was not stored in a dry place before you bought it, it may take as long as a few weeks to thoroughly dry.
A good test is to drip a little water on the wood. If the water gets absorbed, the wood is dry enough to paint. If it beads up, the wood still needs some drying time.
An alternative is to buy a moisture meter. They will measure the moisture content deep inside the wood through tiny holes drilled into the wood. A pin on the meter is inserted into the hole to take the reading. For exterior use, the moisture content should not be higher than 15%. For interior use, it needs to be at or below 12%. If you’re using the wood for cabinet making or furniture, the moisture content needs to be at 6% or below.
If you’re in a hurry, you can buy kiln-dried lumber. This wood is dried in a sort of oven to remove moisture. It is more expensive, of course, but will save you perhaps a month or two of drying time.
Patches – If your wood has large cracks, these should be patched with epoxy resin. You may also need a two-part wood consolidate first. This is a good time to ask your salesperson what to use. Check out my article What is Pressure Treated Wood? A Comprehensive Guide for more information on the risks of using pressure treated wood.
How Do You Paint Pressure Treated Wood?
You’ll need a small brush or two, roller and roller covers, cleaning rags, a clean place to paint, and a place for your primed wood to dry without getting dirty from dust in the air. While you can use a paint sprayer, using a brush or roller to apply the primer is best to make sure the primer gets into every space it needs to.
You’ll also need primer. Choosing your primer is very important. Most sources advise using latex-based primers. Latex is best at coating the wood and keeping the paint from soaking into the wood. However, there are some drawbacks. Latex-based primers won’t stick to cedar wood, for instance.
Some sources advise using oil-based primer, as it tends to cover better, while others urge avoiding oil-based primer. Whatever kind you choose, make sure it is rated for your use, such as an exterior primer for outdoor items.
A good rule is to ask your hardware store personnel for advice. Tell them what you want to use the paint for, including the fact that you’re using pressure-treated wood and what the finished project will be. They can advise you on what kind of paint is best and what primer will go best with it, especially with your local weather conditions.
If you’re using a paint roller, be sure to use a brush first to fill in any small cracks that the primer won’t reach with the roller. Knot holes will need special attention, as they usually feature several small, circular cracks or depressions that will need filling with a brush. Then you can use your roller to go over the whole surface.
Take your time with this, as your primer needs to go on in a thorough coat. Let your primer dry for the recommended time, or longer if possible.
Once your primer is dry, you can apply your first coat of paint. You can use the roller for this, but if you have knot holes in the wood, you may want to use your brush first as you did with the primer. You’ll also need to do this for any obvious cracks. Let the paint dry according to the direction, then you can apply your second coat.
If you’re wondering why you need two coats of paint on top of the primer, this is because the first coat will last only about six months. For a long-lasting finish, you’ll need two coats.
Once your paint is completely dry, you may want to apply a water-repellent coating. Look for one with an ultraviolet stabilizer. This will help keep the paint from being damaged by the sun’s rays, keeping the paint from fading.
The Pros and Cons of Painting Pressure Treated Wood
- Pros – Even with the pressure treatment, the protective chemicals lose their effectiveness over the years. Painting the wood will add protection and may well extend the overall life of the wood. You can also use paint that matches or adds an accent color, adding attractiveness to your home.
- Cons – The preparation of the wood for painting, the priming and painting will take up a lot of time if you have a lot of wood for a big project. If any of the steps are not followed correctly, the primer and paint may not adhere as they should. Your project may be subjected to early paint fading or peeling. If your wood is attractive in itself, you may not want to cover up the wood with paint.
Can You Spray Paint Pressure Treated Wood?
While it’s better to use a roller and brush to apply the primer to make sure you don’t miss anything, you can use a paint sprayer for the paint. While the sprayer will get the primer into all the cracks and other defects, it’s too easy to apply an uneven coat or just not get the primer into all the places it needs to. Primer is important enough that it needs to be applied with some close-up care.
Is it Better to Stain Pressure Treated Wood?
You can stain pressure-treated wood. However, there really isn’t any advantage in staining versus painting. Staining the wood will help in reducing surface cracking. However, since most pressure-treated wood has a sort of greenish cast from the chemicals used in the treating process, you may not end up with the color you want from a transparent stain, especially since you won’t need a primer underneath.
If you want a stain, look for a semi-transparent deck stain. This will give you some color and at least partially counteract any greenish color. Many of these stain products also come with sealants mixed in, giving you a bonus. Make sure you get stain meant for outdoor use.
You can use water-based stain unless your wood has been treated with a water repellent. In this case, you’ll need to use an oil-based stain. If you have doubts or can’t find out just how your lumber was treated, go with the oil-based stain and you’ll have your bases covered.
While you won’t need a primer for the stain, you’ll need to sand the wood to allow the stain to be absorbed into the wood. Here is where you can get creative, as the lower the sandpaper grit number, the rougher the wood will be and the more stain will be absorbed.
The more stain that’s absorbed, the darker the finished color will be. In this way, you have some control over just what color you’ll end up with. You might even sand some boards with one grit and other boards with another, creating a decorative effect.
Can I Paint My Pressure Treated Deck Boards?
It’s certainly possible to paint pressure-treated deck boards. In fact, many of the best paints for outdoor use are labeled as deck paints. Even if you’re not building a deck, you can be sure that paints made to stand up to use on a deck that will be subject to a lot of foot traffic will hold up well on your shed.
What is the Green Stuff on Pressure Treated Wood?
The green color comes from a chemical reaction between the chemicals themselves and the wood. Since copper is commonly used in wood preservatives, what you’re seeing is a bit of that copper patina. Exposure to sunlight and the process of drying will eventually lessen the green color. This doesn’t mean that the effectiveness of the chemicals is necessarily fading, just the color caused by the chemical reaction.
Painting or staining your pressure-treated lumber project does take some time and care, but once it’s done, you’ll have something you can really show off. You’ll also be able to rest easy, knowing that you did your best to protect your project and keep it looking good for years to come.