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Before using wood for fence posts, decks, framing, outdoor furniture, or any other outdoor use, it is good to make sure the wood is pressure treated. Pressure treating wood is the process of infusing wood with preservative products under high pressure. The preservatives protect the wood from rotting due to fungal, insect, and microbial activity. They also make the wood resistant to moisture. If you live in a marine area, the wood preservatives prevent marine invertebrates from boring your lumber.
But should you stain or paint pressure treated wood? In this article, you will learn more about the process of pressure treating wood and whether you should stain the treated wood.
How is Pressure Treating Lumber Done?
Pressure treating wood is one of the most effective methods of treating lumber. The process involves placing the freshly cut lumber or logs in a vacuum and adding wood preservation chemicals. Due to the vacuum in the treatment chamber, the wood preservatives seep deep into the fresh lumber, resulting in green pressure-treated lumber.
Pressure treated wood chemicals
Some of the chemicals used to preserve wood in a wood preserving facility include chromated arsenicals (CCA), creosote, and pentachlorophenol. They are the most effective wood preservation chemicals but are quite toxic.
For that reason, creosote and pentachrolophenol (PCP) are banned for residential use whereas chromated arsenicals are recommended for outdoor use only.
The preservatives protect the wood from rotting and prevent insects and pests from degrading your wood. Other less toxic but less effective preservatives on EPA’s list include Propiconazole, Triadimefon, Acid Copper Chromate (ACC), and Isothiazolinones.
Should you Stain or Paint Pressure Treated Lumber?
Many people wonder if it is ok to stain pressure treated wood and the short answer is Yes! It is good to stain pressure treated wood to seal it from moisture ingress and to protect it from harmful UV light. Also, painting wood with your favorite color makes it look better.
See, pressure treating lumber only protects its internal structure from decaying due to insects, fungal, and microbial activity. But painting or staining wood protects the outer surface from weathering due to harsh external factors such as moisture, rain, and UV light.
For example, if you stain your wood deck, you will protect it from fading when exposed to UV rays. Moreover, applying paint on wood makes it waterproof to prevent water seepage. Needless to say, paint makes a structure look beautiful too.
Therefore, the next step after pressure treating wood is to paint or stain it. Unfortunately, green treated lumber does not absorb paint or stain. So, you must let it dry completely first.
How to dry treated lumber and how soon can you paint it?
There are two ways to dry treated wood. You can either kiln dry the wood or let it sit in the yard to dry naturally (air drying).
Drying wood using the kiln is quick and more effective but a little more expensive. On average, you will pay about 50 cents for each foot. The advantage is that you don’t have to wait for long and you can paint or stain the wood as soon as it comes out of the kiln.
If you choose to let your pressure treated wood dry naturally, you may have to wait anywhere from a few weeks to a year. There is no specific countdown of days. You can keep the wood outside in the open or under a shade. Just make sure there is good air circulation to carry away the moisture coming from the treated wood.
Although the natural drying process seems cheaper, it can be expensive in the long run. First, your lumber may warp if you expose it to direct sunlight or uneven temperatures. Second, there is a cost linked with waiting. Waiting for a whole year to paint or stain your PT lumber is such a long wait. That is why I recommend kiln drying PT wood before using it in your project.
How to tell when pressure-treated wood is dry enough to paint or stain
Whether you are using kiln-dried or naturally dried pressure-treated lumber, it is good to measure its dryness before pouring paint on it. There is no better way to tell when pressure treated wood is dry enough to paint or stain than with a wood moisture meter.
This little electronic device uses the principle of resistivity to measure the moisture level in the wood and show it as a percentage value. You just stick it into the wood and you will get the results instantly.
Some moisture meters for wood are non-destructive. They use an electromagnetic field to measure moisture level. You just place the device on the lumber and viola! You get the results. No poking holes into wood with probes.
The generally acceptable moisture level in well-dried PT lumber should be anywhere between 9% – 12%, give or take 1%. Otherwise, if the wood is too wet, the paint will not stick. And if it is too dry, chances are that the wood has already started cracking or is too thirsty.
You can get a good electric wood moisture meter for less than $50. But if you cannot get one, you can have the measurement done at the commercial kiln drying center or sawmill where you buy your lumber.
Alternatively, if you don’t have a wood moisture tester at hand, you can use water to tell if your pressure treated wood is ready for painting. This is a less accurate method of measuring the dryness of wood but it does the job. This is how you do it.
How to tell if pressure-treated lumber is dry using a drop of water
- Pour a few drops of water on the supposedly dry PT wood
- Wait to see if the water soaks in.
- Paint or wait – If the preservatives have dried off, water will get absorbed into the wood. This means the wood is ready for painting or staining. Otherwise, the drops of water will just bead up without getting absorbed into the wood. In such a case, let the wood sit a little longer to dry or take it back to the kiln.
Conclusion
So, there you have it. You can paint or stain pressure treated wood to protect its surface from weathering. Painting seals wood to prevent it from absorbing water or losing too much moisture. It also makes the wood look beautiful because a coat of paint can conceal the wood grains or any traces of preservation chemicals. Painting wood with your favorite color also makes the wood blend into your decor nicely.
But before staining or painting pressure treated wood, you should make sure it is dry enough. The correct moisture content of pressure treated lumber before painting or staining should be between 9% – 12% for outdoor application and 5% – 9% for indoor use. Anything out of that range will not yield the results you desire.
