Learn about the ins and outs of pressure-treated decking and how to handle its tendency to warp.
You’re in good company if you desire a traditional pressure-treated deck. Even though composite decking is on the rise, more than 70% of decks in America have pressure-treated decking. The relatively inexpensive material is easily accessible and simple to install, and you can customize the finish with whatever color stain you choose. Plus, it’s treated to resist moisture, rot, and insects, so you can enjoy your deck for years to come.
However, this pressure treatment process displays one of the most significant issues with pressure treated decking—it is notorious for warping. Let’s cover why boards warp in the first place, how to pick the best ones for your project, storing boards before installation, and handling warped boards while building.
Why Pressure Treated Decking Warps
American eBuilder details the treatment process, noting that the boards are put into a tank to remove any air in the wood before flushing the boards with chemicals (and water) to resist moisture and insects. This process leaves the boards very wet, making them swell and prone to drying out unevenly. According to The DIY Plan, the wood fibers contracting at different rates shift the overall lay of the fibers, resulting in warping, bowing, cupping, or twisting.
While this first occurs during the treatment process, pressure treated decking continues to undergo these stresses of swelling and drying unevenly each time it gets wet.
How to Pick The Best Pressure Treated Deck Boards
While every pressure treated board is susceptible to warping, there are things you can look for when selecting your decking to get the best boards for the job. The DIY Plan has a comprehensive list of what to look for when selecting pressure treated lumber, which includes looking at the end of the boards when they are in a stack and selecting boards that have narrow growth rings and don’t have the pith (the dark center of the tree) as wood is more likely to move and twist around the pith. It’s also best to select boards where the grain runs straight along the face of the board and to leave any board that already has some curve. Finally, try to purchase the driest pressure treated decking to save time drying it out. Bring a wood moisture meter to check on the moisture content of the boards while at the store.
Alternatively— and if your budget allows —consider buying Kiln-Dried After Treatment (KDAT) decking instead of wet pressure treated boards. As its name suggests, these boards are dried evenly in a kiln after treatment to reduce potential warping, cupping, or twisting. KDAT decking is more expensive; however, if you purchase wet pressure treated boards, you will spend more time allowing them to dry out before installing them.
Storing Boards Properly Before Install
While you can install wet boards as is, you may not have consistent gapping once the boards have dried out, and it adds a lot of stress for your fasteners to keep the boards down. The better option is to allow your decking to dry before installation but be warned: this can take up to a couple of weeks with wet pressure treated decking.
There are a few steps to drying the decking as evenly as possible. First, choose a flat area protected from potential rain. Then lay the decking flat across additional lumber and place stickers between rows to allow for ventilation. Don’t place your decking directly on grass or concrete since the wood will absorb moisture. Finally, put heavy weights, like concrete blocks, on top of the pile of boards to keep the boards as straight as possible.
How to Install Pressure Treated Deck Boards
Before you install the deck boards, pay special attention to your framing to ensure your decktop has the best chance to dry evenly whenever it rains. Be sure the structure allows for proper drainage and airflow to prevent moisture retention in the boards. Your deck surface should be sloped a minimum of 1/4 in. per 12 feet of horizontal run to allow for moisture run-off, and you must have unobstructed airflow under 50% of the deck to allow for sufficient cross ventilation from one side to the other.
When you place the boards, think, “frown down.” That means the rings on the deck board ends are facing downward— the direction of a frown —when laid flat on the joists for fastening. Doing this will reduce the natural tendency for the board to cup upward when it dries.
Spacing is also important to consider. If you install wet boards with a moisture content above 19%, little to no spacing is needed, as the boards will shrink as they dry. However, if you dried your boards or are using KDAT, leave 3/16 in. spacing between boards to allow for expansion and contraction.
With all those factors covered and the right fastener for your job on hand, you can take the final step of fastening boards. But this is where you might have done everything right, but the board still has a bow like you can’t believe. That’s where the CAMO LEVER® comes into play. This tool straightens warped boards effortlessly, and you can even tackle it yourself.
Start by setting your board in place and fastening one end. Then, set the joist width on the LEVER—the Single Joist setting accommodates joists 1-½ in. wide, and the Double Joist setting accommodates joists 3 in. wide. Place the LEVER on the joist at the opposite end of the board and tighten the joist cam with the pivot pin. Apply pressure by moving the handle towards the deck board and keep turning until the board is in the desired fastening position. Fasten the board, then release pressure by moving the handle away from the deck board. Then, loosen the joist cam and remove LEVER. That’s it. Follow this process with each board for a straight deck, then seal or stain the surface for added water repellant and a beautiful, long-lasting deck.
Pressure-treated lumber is still an excellent option for building your deck, so long as you treat it right. With this guide in mind and the proper time and tools for the job, you will have a pressure -treated deck you can enjoy for years to come.