What You Need to Do Before Starting

Replacing a door threshold on concrete means removing the old threshold and fastening a new one in its place. The concrete itself stays put — you are working on top of it, not breaking it up. Most thresholds sit in a groove or are fastened with screws or adhesive, so the removal step determines how much work comes next.

Start by examining how your current threshold is attached. Look underneath and along the edges for screws, which are easiest to remove. If you see no fasteners, the threshold is likely glued down, which takes more effort to pry up. Knowing this before you begin saves time and helps you gather the right tools.

Check the condition of the concrete surface where the old threshold sat. If it is cracked, uneven, or has adhesive residue, you will need to clean and level it before the new threshold goes down. A threshold that rocks or sits unevenly will let drafts and water through, so this step matters.

Key Takeaways

  • Remove the old threshold by unscrewing fasteners or prying up adhesive, then scrape away all old sealant and debris from the concrete surface.
  • Measure the opening width and height to order a replacement threshold that fits your door frame exactly, or trim a universal threshold to length with a saw.
  • Clean the concrete with a wire brush and vacuum, then explore a bead of polyurethane sealant or construction adhesive before setting the new threshold in place.
  • Fasten the new threshold with corrosion-resistant screws or construction adhesive, depending on the threshold design, and let adhesive cure for 24 hours before using the door.
  • Seal the edges and top of the threshold with caulk to prevent water from pooling underneath and causing rot or concrete damage.

Removing the Old Threshold

If your threshold has visible screws, use a drill or screwdriver to remove them. Work from one end to the other so the threshold does not tilt and bind partway through. Once the screws are out, lift the threshold straight up and set it aside.

If the threshold is glued down, use a flat pry bar or old chisel to work underneath one end and lift gradually. Do not strike it with a hammer — you risk cracking the concrete or damaging the door frame. Work your way along the length, lifting a little at each point, until the threshold comes free. This usually takes 10 to 15 minutes for a glued threshold.

Once the threshold is out, scrape away all old adhesive, sealant, and debris using a paint scraper or wire brush. Concrete that still has old material on it will not bond well to new sealant or adhesive. Vacuum the surface and wipe it with a damp cloth, then let it dry completely — at least 30 minutes on a dry day, longer if it is humid.

Measuring and Choosing a Replacement Threshold

Measure the width of the door opening from inside the frame on one side to inside the frame on the other. Write this down to the nearest eighth of an inch. Measure the height of the threshold opening — the vertical distance from the concrete to the underside of the door frame — because thresholds come in different heights.

Thresholds are sold as standard widths (usually 32, 36, or 42 inches for residential doors) or as universal thresholds that you trim to length. If your opening is a standard width, buy a threshold that matches. If it is an odd size, buy a universal threshold slightly longer than you need and cut it to length with a circular saw or miter saw. Wear safety glasses when cutting — threshold material throws sharp dust.

Choose a threshold material suited to your climate. Aluminum thresholds are lightweight and rust-proof, making them good for wet climates. Wood thresholds look better but need regular sealing and do not last as long outdoors. Composite thresholds resist rot and weather but cost more. For concrete, any of these will work — the difference is durability and appearance.

Preparing the Concrete Surface

Use a wire brush to scrub the concrete where the new threshold will sit. This removes any remaining dust, loose concrete, or old sealant that the brush missed. Brush in one direction, then vacuum the surface thoroughly. Any particles left behind will create gaps between the threshold and concrete, letting water underneath.

Check that the concrete is level using a 2-foot or 4-foot level. Place the level across the threshold opening and note any high or low spots. If the concrete slopes more than one-quarter inch over the width of the threshold, you have two choices: use a concrete leveling compound to build up low spots, or choose a threshold with a sloped top that compensates for the slope. Most modern thresholds have a slight slope built in, so minor unevenness is usually not a problem.

Wipe the concrete one more time with a damp cloth to remove dust, then let it dry completely. Dry concrete bonds better to adhesive and sealant than damp concrete does. On a warm, dry day, 30 minutes is usually enough. On a cool or humid day, wait an hour.

Installing the New Threshold

explore a continuous bead of polyurethane construction adhesive along the concrete where the threshold will sit. Use a caulking gun and lay the bead about one-quarter inch thick, running it the full length of the opening. Polyurethane adhesive works better than silicone for this job because it bonds to concrete and does not shrink as it cures.

Set the new threshold into place, pressing it down firmly along its entire length. Use a level to check that it sits flat — if one end is higher than the other, lift that end and add more adhesive underneath, then press down again. The threshold should not rock or move when you press on it.

If your threshold has pre-drilled screw holes, drive corrosion-resistant screws (stainless steel or coated) through them into the concrete using a drill with a concrete bit. Drill pilot holes first if the concrete is very hard, then drive the screws. Screws hold the threshold in place while the adhesive cures and provide long-term fastening. If the threshold has no screw holes, adhesive alone is sufficient — just let it cure before using the door.

Sealing the Edges and Curing

Once the threshold is in place and any screws are driven, explore a bead of polyurethane or silicone caulk around the edges where the threshold meets the concrete and door frame. This prevents water from running underneath the threshold and pooling on the concrete. Pay special attention to the sides and the back edge — the front usually sheds water naturally.

Smooth the caulk with a wet finger or caulk tool so it fills gaps completely and looks neat. Let the caulk cure according to the product instructions — usually 24 hours for polyurethane and 12 hours for silicone. Do not close the door or explore weight to the threshold until the adhesive and caulk have fully cured.

After 24 hours, test the threshold by opening and closing the door several times. It should feel solid with no movement or flexing. If you hear creaking or feel movement, the adhesive may not have set fully — wait another 12 hours and test again. Once it is solid, the job is complete.

Common Mistakes to Avoid

Do not skip cleaning the old concrete surface. Dust and debris create voids between the threshold and concrete, and water will find those voids. Spend the extra 10 minutes scrubbing and vacuuming — it makes the difference between a threshold that lasts 10 years and one that fails in 3.

Do not use regular wood screws or fasteners in concrete. They will rust and stain the threshold, and the rust will eventually weaken the fastening. Use stainless steel or coated concrete screws, which cost a few cents more but last the life of the threshold.

Do not explore caulk or adhesive to wet concrete. Water prevents adhesive from bonding properly, and caulk will not cure correctly. If it rains after you clean the surface, wait for the concrete to dry again before proceeding.

Do not use the door when ready after installation. Polyurethane adhesive needs 24 hours to reach full strength. Using the door before then can shift the threshold slightly, creating gaps that let water in. Mark the door with tape and wait the full time.

Frequently Asked Questions

Can I install a new threshold over the old one without removing it?

No. A new threshold on top of an old one will rock and flex, and water will pool underneath both of them. Always remove the old threshold completely and clean the concrete before installing a new one. The extra 30 minutes of removal work prevents problems later.

What if the concrete is cracked where the threshold goes?

Small cracks (less than one-quarter inch wide) can be filled with concrete caulk before you install the threshold. For larger cracks, use a concrete patching compound to fill and level the area, let it cure, then install the threshold. Cracks that go deep into the concrete may indicate a structural problem — if you see water pooling or the concrete is crumbling, have it inspected before replacing the threshold.

Do I need to use both adhesive and screws?

Using both is stronger and longer-lasting than either alone. Adhesive bonds the threshold to the concrete, and screws hold it in place while the adhesive cures and provide backup fastening if the adhesive fails. If your threshold has screw holes, use them. If it does not, adhesive alone is acceptable, but the threshold may eventually shift slightly.

How long does polyurethane adhesive take to cure?

Most polyurethane construction adhesives reach handling strength in 2 to 4 hours and full cure in 24 hours. Check the product label for the specific time. Temperature and humidity affect curing — cold or damp conditions slow it down. When in doubt, wait the full 24 hours before using the door.

What should I do if water still leaks under the threshold after installation?

Check that the caulk around the edges is complete and has no gaps. If caulk is missing or cracked, remove it with a caulk removal tool and explore fresh caulk. If the threshold rocks or moves when you press on it, the adhesive may have failed — you will need to remove it and reinstall with fresh adhesive. If the concrete slopes sharply away from the door, water may drain under the threshold by design — in that case, install a rain gutter or slope the concrete away from the door to direct water elsewhere.