Install a floating subfloor over concrete slab
Before you begin
- Check your local building code, and pay special attention to rules concerning vapor barriers, span ratings (subfloor thickness) and floor drains.
- Use a digital moisture detector to measure the moisture content (MC) of the concrete slab.
- Read the flooring manufacturer's guidelines for the product you plan to install, and pay particular attention to requirements as regards the structure and moisture content of the concrete slab.
- Manufacturers may require sub-floor and flooring materials to be acclimated prior to installation (generally 24-72 hours).
Calculate the materials required
- 1.1 - Measure the length and width of the room
- 1.2 - Multiply the length of the room by the width to determine the surface area (square footage) to be covered.
- 1.3 - Divide the total surface area by the surface of one panel. Most floating subfloor panels measure 2' x 2' but check the precise measurements with the manufacturer. The result of your calculation will provide you with the exact number of panels needed.
- 1.4 - Add 10% to the total in case of error or defective pieces.
Prepare walls and doors
- 2.1 - Remove existing baseboards, mouldings and doorway thresholds.
- 2.2 - Measure the combined thickness of the subfloor and finished floorcovering.
- 2.3 - With a saw or oscillating tool, cut door casings and jambs to 1/16" above the level of where the finished floor will be.
- 2.4 - If necessary, remove the doors and use a circular saw to cut 1/8" above the level of where the finished floor will be. (The bottom of a hollow-core door can only be cut to a limited extent. Never cut the top of the door.)
Level and clean the slab
- 3.1 - With a metal straightedge, identify dips or high spots that exceed recommended tolerances for the floor you are installing (usually within a variance of 3/16" every 10 feet or 1/8" every 6 feet).
- 3.2 - Use a concrete grinder to level high spots.
- 3.3 - Fill low spots with self-levelling compound or Portland cement. Follow the compound manufacturer's recommendations regarding surface preparation, mixing and drying time.
- 3.4 - Clean up construction debris: loose concrete, paint, adhesives, and dust.
- 3.5 - Fill cracks with concrete filler and smooth out the surface with the flat edge of a trowel.
- 3.6 - Allow the filler to cure, then seal with water-based polyurethane.
Determine the layout
- 4.1 - Choose the longest straight wall as your starting wall.
- 4.2 - Check your starting corner for square. If the angle is greater than 90º, trim the edge of the panel to maintain a ¼" gap along the wall.
- 4.3 - Ensure that the last panel will be at least 3" wide. If necessary, cut the first panel.
Install the first row of panels
- 5.1 - Beginning in the 'start' corner, place ¼" spacers along the walls.
- 5.2 - Install the first panel with the tongue-side flat against the spacers.
- 5.3 - Insert the tongue of the following panel into the groove of the first.
- 5.4 - Place a block of wood (tapping block) against the edge of the second panel and tap with a rubber mallet to ensure a tight seam.
- 5.5 - Continue with the other panels in the first row.
- 5.6 - Ensure the panels are level as you proceed and use levelling shims when necessary.
- 5.7 - Measure the space for the last panel and cut. Maintain the ¼" space.
- 5.8 - Use a pull bar to install the panel.
- 5.9 - Check the first row for level and adjust with shims if necessary.
Install the remaining rows
- 6.1 - Stagger the seams for subsequent rows. Cut the first panel, maintaining a minimum 3" width.
- 6.2 - Maintain the ¼" space along the wall.
- 6.3 - Cover the entire surface area, staggering the seams in each row.
- 6.4 - Always check for square and adjust with shims when necessary.
- 6.5 - Measure and cut to fit the panels for the last row. Maintain the ¼" space against the wall.
- 6.6 - Use a pull bar to insert panels.
- 6.7 - Remove the spacers along the walls. The space allows for expansion and contraction and will be concealed by baseboards.