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Before using wood to make fence posts, decks, or other structures in your construction project, treat it first. Treating wood refers to the process of infusing it with preservative products. The preservatives protect the wood from rotting due to fungal, insect, and microbial activity. If you live in a marine area, the wood preservatives prevent marine invertebrates from boring your lumber. After treating wood, you can now stain or paint it to protect its surface.
Treating wood by pressure treatment
One of the most effective methods of treating lumber is pressure treating it. The process involves placing the freshly cut lumber or logs in a vacuum and adding wood preservation chemicals. Due to the vacuum, the wood preservatives seep deep into the wood, resulting in pressure treated lumber.
Wood preservation products
Some of the products used to preserve wood include chromated arsenicals (CCA), creosote, and pentachlorophenol. They are the most effective but quite toxic. For that reason, creosote and pentachrolophenol (PCP) are banned for residential use whereas chromated arsenicals are recommended for outdoor use.
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.
Staining or painting pressure treated lumber
Is staining or painting pressure treated wood necessary? This is a question that comes up quite a lot and the simple answer is Yes! Treating lumber only protects the internal structure of wood from decaying due to insects and fungal and microbial activity. Painting or staining protects the outer surface of wood from weathering due to harsh external factors such as rain and UV rays. For example, staining your wood deck protects it from fading when exposed to UV rays. Similarly, applying paint on wood makes it waterproof and blocks harsh sun rays. 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, freshly treated lumber does not absorb paint or stain. So, you must let it dry completely first. Otherwise, your effort will go to waste and the surface of your wood will not be protected.
How do you dry treated lumber and how soon can you paint it?
There are two ways you can dry treated wood. Either you kiln dry or letting it sit in the yard to dry naturally. 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 and you can paint or stain the wood as soon as it comes out of the kiln.
If you choose to let your PT 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 pressure-treated lumber is such a long wait. That is why I advocate for kiln drying PT wood before using it to construct.
How do you tell that pressure-treated wood is dry and ready for painting or staining?
Whether you are using kiln dried or naturally dried pressure-treated lumber, it is good to measure its dryness before pouring paint on it. The most professional way to do this is using an electric moisture meter. The tool uses two electrical probes to measure the electrical resistance of wood sample. The method is quick, more accurate , and non-destructive
A high resistance value (thousands of megaohms) indicates dried wood while lower resistance values indicate wet wood. In other words, the resistance is higher for dry lumber than wetter lumber. In terms of the percentage of moisture content, well-dried lumber should have anywhere between 6% and 12% moisture saturation.
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 moisture meter for wood handy, you can use water to tell if your PT wood is ready for painting. This is a less accurate method of measuring the dryness of pressure treated wood but it does the job. I use it all the time. 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.