A threshold is a raised base within a doorway that provides a transition between the interior and exterior spaces, as well as typically integrates with a weatherseal for the bottom of the door. Whether you are installing a new threshold as part of a new door frame or replacing a worn or damaged threshold to restore the doorway, when you are attaching a threshold to a concrete floor, following a standard procedure will ensure a lasting connection to the floor surface.
Remove the rubber weatherstripping from the threshold, if applicable, to expose the screw holes in the threshold.
Measure the width of the door opening between the vertical jambs and cut the threshold to length, as needed, to fit between the jambs and align the door channel with the door. Use a hacksaw for metal thresholds and a handsaw for wood thresholds.
Preset the threshold into place in the doorway opening and mark each of the screw hole locations on the concrete's surface using an awl or center punch. Gently tap the awl or center punch with a hammer to dimple the concrete surface to easily identify the locations for drilling.
Drill a hole in the concrete at each of the screw locations marked in Step 3 using an electric drill mounted with a 5/16-inch masonry bit. Bore the holes to a depth that allows the top of the screw shields to fit flush with the floor surface. When each hole has been drilled, blow out any residual concrete dust and insert a screw shield.
Apply a continuous 1/4-inch bead of silicone caulking on the bottom of each long edge of the threshold. Some aluminum thresholds have a prefitted rubber gasket at each edge and, in this case, the caulking can be omitted.
Hold the threshold slightly above the concrete floor surface and move it into place in the doorway, then lower it onto the floor to spread the the caulking.
Insert a flathead screw into each of the screw holes and thread the screws into the screw shields using a screwdriver until tight.
Trim the rubber insert to the necessary length using scissors or a utility knife and press it into the threshold channel, if applicable for the threshold. Close the door to insure proper clearance and seal at the weatherstripping.