How to Install Mahogany Tongue and Groove on an Outside Porch
Mahogany’s natural disease and weather resistance makes it a long-lasting, traditional choice for porch floors. Tongue-and-groove flooring is best installed perpendicular to the floor joists, whether inside a home or on a porch or deck. Porches usually do not have a solid subfloor, such as plywood, so the joists are clearly visible. Most porches are built with joists running parallel to the front of the house, so flooring runs from the front of the house out to the front edge of the porch. Although mahogany is durable, sealing it adds another measure of protection.
Place a straightedge lengthwise on the face of a piece of flooring. Align it just behind the groove and trace its edge on the flooring with a pencil.
Set the fence or guide on a table saw to the measurement that you will trim off the grooved edge of the first piece of flooring. Cutting off the groove leaves a clean, flat edge along the flooring at the end of the porch. Turn on the saw and push the flooring board through the blade, keeping the grooved edge of the board against the fence. If you do not have a table saw, you can trim off the groove with a circular saw or jigsaw.
Set the trimmed piece of flooring board across the joists at one end of the porch. Leave a 1/8 inch gap between the short end of the flooring and the front of the house. Adjust the board to allow the trimmed, flat edge to overhang the edge of the porch by 3/4 inch.
Drill one hole through the face of the board close to the trimmed edge at each joist, including the rim joist or outermost joist. Use a power drill and a drill bit that is the same size or slightly smaller than the diameter of the 8d galvanized, spiral decking nails. Drive one decking nail through each hole and into the joist with a hammer.
Place the tip of a decking nail against the back edge of the tongue on the opposite edge of the board. Angle the nail toward the flooring, not straight down, and drive the nail through the tongue and into the joist. Repeat along the tongue at each joist.
Tap the head of each nail with a nail-set tool and a hammer to sink them below the surface of the tongue.
Place the grooved edge of the second board against the tongue of the board that you just fastened. Push the second board against the first, fitting the tongue and groove together snugly. If they resist, set a scrap block of wood against the tongue of the second board and tap them together with a mallet. The scrap of wood protects the tongue from the mallet.
Drive one nail at an angle through the tongue of the second board and into each joist, as you did with the first board. Continue across the porch but stop before installing the final board. There is no need to drill through and nail the face of the second or remaining boards, until you reach the final one at the opposite end of the porch.
Measure from the edge of the last fastened board to the end of the porch, plus 3/4 inch for the overhang. As you trimmed off the groove of the first board for a clean, straight edge, you will also trim off the tongue of the last board. Mark the last board with that measurement, then trim off the tongued edge with a table, circular or jigsaw.
Fit the final board against the last fastened board. There is no tongue to nail through, so drill through the face and nail it to the joists as you did with the first board.
Mark the top, front edge of the first and final boards on the porch 3/4 inch past the front edge of the porch. Pull a chalk line across the edge of the porch between the marks, and snap it to make a straight cutting line.
Cut across the front edge of the flooring with a circular or jigsaw, following the chalk line and leaving a straight, 3/4-inch overhang across the front edge of the porch.
- Mahogany is a dense wood. If you use a jigsaw, you will need a heavy-duty, fine-tooth blade.
- Some professional installers recommend wrapping each joist with tar paper before installing the floor to help extend its life.
- Apply water sealer to the mahogany flooring after it is installed, if you desire. Use a brand that is made for mahogany, and follow the manufacturer’s instructions.
- If your porch has complicated railings and balusters to work around, measure, mark and cut each board to fit around the obstacles. A compass can help you transfer the precise angles of the obstacles to the flooring, which allows you to cut them for a tight fit.
- Wear eye protection whenever you operate power saws.
- Do not glue the joints unless the flooring manufacturer specifically recommends it. Gluing can cause the floor to split.
- Table saws can be quite dangerous. Use a long scrap of wood to push the end of the board through the blade to keep your hands at a safe distance.
Carole Oldroyd, a writer based in East Tennessee, has authored numerous DIY home improvement, Human Resources, HR and Law articles. In addition to holding a degree in paralegal studies, she has more than 10 years of experience renovating newer homes and restoring historic property.
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