How to fasten wood to a concrete block

Attaching wood to CMU (concrete masonry unit) is possible using several procedures. Determine how much stress the fastener needs to resist for the connection between the concrete block and the wood. Additionally, determine if you must make the connection removable or permanent. All of the fastening methods for this application are easy for the do-it-yourself handyman.

Clean the CMU block with a stiff scrub brush. The adhesive will not stick to the CMU block if layer of dust or debris is on the surface.

Squeeze the caulk gun to apply construction adhesive to the back of the wood. You do not need a lot of adhesive to secure the wood in position. Place dabs of adhesive about 12 inches apart on the back side of the wood.

Press the wood into position, then secure it with painter's tape until the adhesive sets. Painter's tape will come off easily and will not leave any sticky residue behind. For large pieces of lumber, brace them in position until the adhesive dries. The glue method is a permanent means of fastening. It will also withstand a lot of stress before the bond breaks.

Mark the locations for the placement of the concrete screws into the CMU block. The screws must be within the CMU block and not at a joint between blocks. The screws will not hold in the joints' concrete mortar.

Pre-drill holes into the wood for the concrete screws. Use a countersink drill bit for this step. Countersink the wood enough for the top of the concrete screw to be below the surface of the wood.

Hold the wood in position against the CMU block. Use a marker to mark the exact location for all the screws onto the CMU block.

Install a concrete drill bit, the size of the screw, into a hammer drill. Place a piece of painter's tape on the drill bit to indicate the depth needed to drill. This will be the length of the screw minus the depth of the wood plus 1/4 inch.

Blow the holes out with a can of compressed air. Use a power screw driver to secure the wood to the CMU block with the wood screws. This method of fastener is removable. However, it is not as strong a connection as the glue method.

Place a PAT (powder-actuated tool) charge into the chamber of the PAT gun. Load a PAT nail into the tip of the PAT gun. Refer to the labels on the box of nails and charges to determine the correct ones for your application. The strength of charge is determined by the thickness of material attached to the concrete and its hardness.

Hold the wood in position against the concrete block.

Place the tip of the PAT gun against the wood where you want the fastner installed. Pull the trigger and the PAT gun will fire the nail through the wood and into the CMU block. The nail stops where it hits the built-in washer. This method of fastener is permanent and is a strong method of attaching wood to CMU block. However, the fastener is visible and left above the surface of the wood.

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