The minimum recommended spacing for most composite deck joists is 16 inches on center. If you are laying your boards on a 45 degree angle, you’ll want your joists spaced at 12 inches on center.
If you are updating a much older wooden deck, there’s a chance that the joists may be set 24 inches on center. Unless they are severely water damaged, leave the old joists in place as supplemental support in addition to your new 16″ center joists.
A handy trick for making sure your joists are level with the rim joists or ledger is to attach a strip of wood to the top of each end of the joist, overlapping each end of the joist by a few inches. This will allow you to hang the joist on the ledger or rim joists while you toenail or set a joist hanger.
Protecting Joists From Rot
Composite decking manufacturers recommend applying deck flashing to the tops of joist to protect them as well as the screw holes from moisture damage which will eventually rot the screw fasteners. The butyl flashing tape not only protects the joists, it also makes the joists less noticeable from above. If you’ve repaired or replaced decks before, you’ll likely have noticed that the fasteners and the ends of the joists usually rot due to moisture damage first. Priced anywhere from $20 to $40 for 50 linear feet per roll, the tape can get fairly expensive especially if you have a large deck.
Roofing felt or tar paper are used as underlayment in roofing. They are coated/saturated with either asphalt or tar for waterproofing. One $20 roll can cover up to 200 to 400 square feet, which would be more than enough for the standard deck. It would need to be cut into strips and stapled into place. While it won’t provide the same protection for fasteners as butyl tape, its waterproofing capabilities will help reduce the amount of moisture sitting on the top of joists.
Another option is to use concrete or garage floor epoxy paint. It has excellent adhesion and waterproofing capability, is easy to apply, and costs about $34 a gallon. The bonus is that it comes in an assortment of colors, allowing you to closely match your composite deck boards. You can even paint the ends of your joists (the ends usually rot before anything else).
Composite Decking Board Spacing
Most composite deck manufacturers recommend a minimum of 1/8 inch to 3/16 inch spacing between running boards to allow for heat expansion, with a maximum spacing of a 1/2 inch, if you are screwing in your boards versus using hidden fasteners.
If you have a lot of trees on your property and spend more time than you’d prefer cleaning up pine needles in the summer or leaves in the fall, you’ll likely want to opt for at least a 3/8 inch gap between boards. The 3/8 inch gap will allow you enough space to clean out all the debris that will end up in between your boards each season. Regardless of spacing, the grooves in the composite boards will eventually accumulate a build up of debris over time.
Removing Rust Stains From Composite Boards
Composite deck boards can become stained with rust from powder coated steel patio furniture, metal plant stands, grills and other items on the deck. The only product that has worked for us in removing the rust stains from our Trex Transcend boards is CLR Calcium, Lime & Rust Remover. Just pour a small amount of CLR over the stain, work it using a small scrub brush and let it sit for a few minutes before rinsing. Deeply embedded rust stains make take 2 to 3 treatments with CLR. Always test an inconspicuous portion of your deck board first before using it.
Repairing Scratches On Composite Deck Boards
Scratches on composite decking boards from patio furniture or pets are not uncommon. If the boards have a smooth surface, you can lightly sand the scratches using steel wool. A heat gun can help soften the appearance of light scratches on smooth boards; test an inconspicuous area before trying this method.
For composite deck boards with a wood grain texture, you’ll need a filler and an artistic touch to conceal scratches. There are a few composite deck repair kits available, but avoid those that use wax, which will melt as soon as the summer sun hits the repaired area. An epoxy putty is your best bet for filling scratches in boards with a wood grain pattern. You will need an epoxy that can be tinted in order to match your deck’s color. Loctite Epoxy Gel can be tinted with earth pigment powders, powders that are made from ground minerals. Once you have applied the epoxy to the scratch, use a toothpick or other narrow tool to contour the repair to match the wood grain.
For our Trex Transcend board that had deep scratches, we played with a scrap board and discovered that the jagged edges of the scratch could be softened and smoothed out using parchment paper and an iron set at medium high. We then used a soldering gun to re-create the subtle lines in the surface to mimic the existing wood grain.
Filling Holes In Composite Deck Boards
If you screwed in your composite deck boards or have a small hole due to damage, there are a variety of plugs you can buy to conceal the holes. Prices start at $22 for 75 plugs. If you only have a few holes to plug or a small damaged area to fill, you’re better off using the same epoxy putty method used to repair scratches that was previously mentioned above.
If you are filling several hundred screw holes and are looking for an alternative to spending a couple of hundred dollars on pre-made plugs, you can make your own using leftover composite board and a tapered plug cutter.
Removing Tree Sap From Composite Deck Boards
Traditional methods of removing tree sap from surfaces, such as heat guns, harsh chemicals, and scraping, may damage your composite deck boards. The best method for removing tree sap is to soak a cotton ball in isoprophyl alcohol (rubbing alcohol) and set over the sap until it begins to break down.