Where should Tapcons go to anchor a French Door threshold to a concrete slab and how can the screw heads be hidden effectively for durability against weight strain?
Asked by Susanne Jekel 
6 months ago
Last Updated: June 8, 2024
I’m trying to secure the threshold of a French Door to a concrete slab. I’ve heard I can use screws or adhesive. I lean towards screws like Tapcons, but I’m not sure where they should go or how to hide the heads.
There are plugs, but they seem to cover adjustment screws, not access to the plate. Using adhesive seems easy, but I’m not sure what type to use. I’ll be driving my mower over this area, and I’m worried about the strain from the weight. What do you think I should do? Thanks!
The bolt holes should align directly under the plastic caps.
Hey David, I had the same idea, but they seem to be covering the adjustment screws for the threshold.
Hey Mitch, have you checked under all of them? Some might need adjusting and some might be for anchoring
I haven’t had to deal with an aluminum threshold in a long time. I completely forgot about those door height adjusters underneath.
I could check under 2 or 3 of them, it wouldn’t take much time and wouldn’t cost me anything.
That’s a valid argument.
Perhaps I should remove the entire strip covering the adjustment screws and install some anchors in between?
I drilled a hole for the pin on the ‘fixed’ door to latch. I could insert a screw in that hole to create at least one solid anchor point. Then use adhesive for the rest?
Suggests using Tap cons. If you need to make adjustments to the strip or replace it, you can simply remove them. If you glue it in, you’re stuck with it, even if it fails or gets damaged. I’ve had to replace them before. I’ve been a contractor for many years.
I usually use an anchor there and sometimes remove one adjustment screen to pass through with an anchor
If all the plugs are meant for adjustment screws, you can purchase plugs, drill a hole in the top, insert your tapcon, and then seal it with the plug. Additionally, consider using adhesive along with screws.
Was that threshold connected to the door when it was put in? If it was, the adhesive should have been placed underneath at that point.
If it’s not connected, or if you can detach and reattach it, try flipping it over to check for screw holes. If you find them, unscrew the adjustment screws under the caps and separate the adjustment plate from the mounting plate. Then, drive screws through the holes into the floor. If no holes are present, use construction adhesive to secure it back to the frame.
If you’re unable to detach it from the frame, it should have had adhesive underneath during installation. However, there might be enough flexibility to slide the adhesive tube nozzle underneath and apply it anyway.
Regardless of Tapcons usage, applying adhesive is essential to prevent water from seeping into the house. I recall one instance where a solid bead of adhesive was applied along the inside edge and a broken line along the outside edge. This setup allowed water to escape only through the broken line to the outside.
Thanks for your help. So, the threshold, frame, and doors all came pre-hung. The installers didn’t bother to use adhesive, but I managed to add some in. Any specific type you recommend? Thanks once more.
The threshold is already attached to the frame, so you just need to focus on keeping out water, pests, and hot or cold air. You can use any construction adhesive like Loctite, OSI, Sikaflex, or something elastomeric – silicone may not be the best choice. A single bead inside should be sufficient, but if it’s already on the floor, consider putting down two beads inside. On the outside, just squeeze a few short dabs to keep it from lifting up without creating a line across the front and trapping water.
Yeah, that’s right. The ends are secured by the frame on the sides, so it can’t really move unless it bends a lot or something. I just want it to stay in place. Every time I drive my little tractor over it, it will probably shift slightly. The more it shifts, the more I worry it might come loose.
Before installation, it’s a good idea to apply a weatherproofing/adhesive. Just prop it up, apply a generous amount of sealant/adhesive underneath, close the doors, and keep them shut for a day. Adjust the threshold slightly higher to ensure it gets enough pressure when the doors are closed.
Appreciate it. Do you have a favorite adhesive brand?
OSI QUAD from Home Depot is really effective. It can be a bit tricky to work with, and once it’s on something, it’s not coming off easily. Liquid nails max fuse is also great, but it’s just glue, not a sealant.
Make sure to use 100% silicone and nothing else
Apply construction adhesive underneath the threshold, drill holes using a 3/16 masonry bit, insert concrete anchors of the same size, and countersink panhead screws of 3/16 to be flush with the frame. This will secure the threshold in place permanently. Finally, caulk the screw heads with a matching color.
The rail where the adjustment screws are located should come off as one piece, making it easier to reach the underside of the track from above😉
I’ve attempted to remove it, but it’s really stuck. I had to stop because I was starting to scratch the surrounding areas. I’ll take a break for now.
Hey, no worries. I thought that lip might detach from the inside. I’ve seen similar setups in sliding door tracks and exterior door tracks. I would recommend placing the screws and anchors more towards the outer part of the frame. How far does that lip extend over the slab? If a mower goes over it, it might bend or deform. Adding a 1×1 underneath could also help. Just throwing some ideas out there. Keep me posted on how it goes, okay?
Hey, I appreciate the suggestion. For the shed, I think using Tapcon flat head screws to secure the aluminum plate of the threshold is a great idea. The blue heads might not stand out too much, especially once they get a bit dirty and weathered. I just really want to make sure that threshold is firmly attached to the slab. If it weren’t for the doors, I’d actually prefer not having a threshold at all.
You should consider using silicone along with a screw.
If it were me, I’d grab a couple of tubes of sikaflex and apply it underneath the track in various spots. Then, adjust the doors just right, shim them, and let them sit as long as possible. Maybe do it on a Friday evening and allow it to set over the weekend. It should hold up quite well
There should be a removable plate on the underside, or you could create one. Attach the plate to the concrete first and then attach the piece to it.
Start by removing all the caps and adjustment screws. Once the top piece is off, you will be able to access the metal track. Secure the metal track with tapcons, then re-install the top piece and adjustment screws.
Oh, I see now how that thing can be disassembled. 👍
I’m pretty sure, Mitch. I’ve done it a few times with a standard door.
Make sure the sill is in the right place before lifting it up to apply silicone underneath from both sides. This will prevent any mess. Also, consider placing a kickboard under the sill on the outside to prevent movement when stepped on.
They’re adding a concrete ramp on the exterior. It will provide support for the protruding lip.
Even more amazing
I suggest removing it and adding a sweep to the bottom of the door. If you plan on driving over it, you’ll be struggling with that issue constantly. Best of luck! ✌
I’m thinking I need a method to secure the doors. 🤔
Hey, do you know how they’re pinned currently? Maybe check out Home Depot for some ideas.
The door I installed is ADA compliant, allowing me to easily move hand trucks and other items across it. The threshold is quite flat with ramps on both sides leading to the floor. Perhaps consider adding an ADA threshold and a bottom sweep for improved functionality based on your regular needs.