Pressure-treated lumber has been a great innovation for the building industry. The treating process has helped further extend the life of this already renewable resource. In some cases, the lumber now lasts as long as the time it takes to grow and harvest the next planting.
Know what you’re signing up for with appearance-grade treated lumber
It’s important to remember the limited lifetime warranty for pressure-treated lumber only protects against rot, decay, and termite damage. Should your pressure-treated lumber have issues in the future with rot or termites, you'll be eligible to file a warranty claim to receive replacement material. Labor is not included in the warranty and it requires that any cuts or holes made in the field are properly treated.
Wood does “what wood does”
It can be easy to think that behaviors like splitting, checking, warping, and twisting should be included in the warranty for pressure-treated lumber. The fact is, they are not. Wood is prone to these types of behaviors, and depending on the species of lumber, some can be more severe than others. In the state of Washington, a large percentage of pressure-treated lumber is made using western hemlock. (If you've ever seen untreated hemlock lumber on a job site after it’s been exposed to the elements, you’ll know what I'm talking about.) If moisture is introduced to the wood through the treating process, there's an elevated risk of wood movement.
What to do during construction
So, having knowledge of this dilemma, how should one proceed in a way that helps to minimize the effects of the weathering process? Although you might be tempted to wait until the project is finished, in this case, it's recommended that you apply the protective finish at the end of each day during the construction process. The recommended product is Wolman RainCoat (clear, oil-based) Water Repellant.
Sweep off the pressure-treated decking each day, and apply a thin coat of the product. Putting it on too thickly will prevent the repellant from drying in a timely manner, which will create a bit of a challenge. Should this happen, the boards can be wiped down with lacquer thinner to remove some of the excess.
Why should you apply protective finish each day during construction?
A lot of moisture is introduced into the wood during the pressure-treating process. By applying the Wolman RainCoat waterproofing sealer as soon as possible, you’re attempting to help the appearance-grade treated boards dry out more slowly. In a “perfect world,” I would love to install appearance-grade lumber in 50-degree weather, with cloud cover, fog, and a light breeze—have that weather pattern last for 60-plus days. That would be a perfect scenario for helping the wood dry slowly. We know that weather scenario is likely to never be the case, so taking steps to slow the drying process is our next best option. A certain amount of checking and splitting is inevitable, but following this best practice will help to minimize it.
Ongoing maintenance for treated lumber
Following a regular maintenance schedule for your appearance-grade treated wood will help keep it looking its best. The wood comes pre-stained from the factory, so as long as the color is still acceptable, you can keep applying thin coats of the clear Wolman RainCoat product as needed. A good rule of thumb is to apply a fresh coat when you see the water no longer beading up on the wood. If, at some point, you feel the color needs a refresh, you can switch gears and apply a coat of Wolman F&P Finish and Preservative, a transparent penetrating oil finish that comes with a color toner.