Fastening Wood Flooring to Concrete

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Moisture Considerations

• Prior to installing a wood floor, the building should have been completely enclosed - with all windows, doors, and sheetrock installed.  Heating should have been on for a minimum of 5 days before installation. In summer weather, the area must be well ventilated.
• Concrete must be a minimum of 30 days old.
• The surface of the concrete must be flat and free of oil, grease, and dust.
• Always use a moisture bearer, which is usually placed between the subfloor and the finished floor.

Fastening Subfloor

Most professional installers use two methods for attaching the subfloor to the concrete. The two methods have one thing in common - the head of the fastener once installed is flush with the surface of the subfloor. This is critical because it ensures that the finished floor will sit flat on the subflooring. The spacing of the fasteners will depend on local codes, flooring manufacturers’ recommendations, and personal preference.

Using Split Drive Anchors

The split drive anchor is a one piece, fast and easy-to-install concrete anchor that comes with a flat countersunk head. Split drive anchors are called pre-expanded expansion anchors. The anchor is manufactured larger than the hole in the concrete that it will be installed in, and, once installed, exerts outward pressure trying to get back to its original shape. This one-piece anchor is available in only one diameter of ¼”; the hole size to be drilled in the concrete is equal to the diameter of the anchor - ¼”.

• Length - the length of a split drive anchor to use for fastening wood to concrete is determined by adding the thickness of the wood to the minimum embedment of 1-1/8”. For example, if the sleeper is a 2x4 then the thickness of the wood would be 1-1/2”. Adding the minimum embedment of 1-1/8” would then equal 2-5/8”, making it correct to use a 2” split drive anchor. The split drive diameter is measured as an overall length that includes the head.
• Anchor Spacing – the minimum distance between split drive anchors in the expansion anchor industry is 10 anchor diameters between anchors, or 2.5” and 5 anchor diameters, or 1-1/4” from an unsupported edge. The reason is that once set the split drive anchor is installed it exerts forces against the concrete, if the anchors are installed too close together then these forces may interact and reduce holding values.
• Installation: (1) With the plywood or sleeper in place, use a hammer drill and ¼” carbide tipped masonry bit that meets ANSI standards. Drill right through the wood and into the concrete to a depth of ¼” deeper than the split drive anchor will penetrate the concrete. (2) Clean the hole out of all dust debris, using a wire brush or compressed air. (3) Insert the split drive anchor through the hole in the wood and into the hole in the concrete. (4) Strike the head of the split drive anchor with a hammer until the head is flush with the surface of the wood subfloor. A link to a video on “How to Install Split Drive anchors” is provided.
• Sizes and Packaging – the split drive anchor is packaged in a box of 100 pieces with 10 boxes in a case of 1000.

Tapcon Masonry Screws

The Tapcon screw is a self-tapping concrete screw that taps threads into a predrilled hole in the concrete. Tapcon is the original American concrete screw with advanced threadform technology that requires less torque, making them easier to install. The Blue Climaseal™ provides extended corrosion resistance.

• Head Style – tapcons come in two head styles; the flat Phillips countersunk style is the head style to use for putting subflooring down.
• Diameter – They are available in the 3/16” diameter and 1/4” diameter. The ¼” diameter provides greater holding value; most professional installers use the 1/4” diameter.
• Length – to determine the minimum length of Tapcon to use for any specific application add the minimum embedment depth of 1” to the thickness of the wood being attached. If a 2x4 is being used as a sleeper then add 1” to the 1-1/2” for a minimum length of 2-1/2”. The closest Tapcon length over the 2-1/2” is 2-3/4”. The maximum embedment for a Tapcon in the concrete is 1-3/4”, so the longest screw for this 2x application would be 1-3/4” plus 1-1/2” or 3-1/4”. Therefore, the closest Tapcon to meet this requirement would be the 3-1/4” Tapcon.
• Hole Diameter – the hole to drill in the concrete for ¼” flat-headed Tapcon screws is 3/16” and must be drilled using a hammer drill that is set in the hammer and rotation mode.
• Approvals – Miami-Dade #07-0315.03 and is ICC-ES listed report number ESR-1671.
• Installation: (1) For the ¼” Tapcon drill a hole, use a hammer drill through the wood subfloor using a 3/16” carbide tipped ANSI standard bit.  The depth of the hole should be at least 1/2” deeper than the Tapcon will penetrate the concrete. This leaves space for any dust and debris created during the installation to fall. (2) Using a vacuum, wire brush or compressed air, clean the hole of all dust. (3) Insert the screw through the wood and into the hole in the concrete, use a rotary drill and #3 insert bit to install the screw until the head of the screw is flat with the surface of the wood.
• Follow this link for an instructional video on “How to Use Tapcon Screws”.
• Packaging - All Tapcon masonry screws are sold in boxes of 100 pieces with one correctly sized carbide tipped bit included for free. Each case has 5 boxes of screws for a total of 500 Tapcons.

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