We have just had an extension built but there is now a large gap between where the concrete step from the external door used to be and the wood floor that has been built next to it. We are just about to have vinyl flooring laid down and I’m looking for the best solution to fill the gap.

I’m thinking a thin sheet of 1.00mm metal laid over it is my best bet. Struggling a little and any help would be much appreciated!

enter image description here

  • What's supporting the subfloor?
    – Huesmann
    Sep 22 at 13:46

3 Answers 3


You don't bridge something like this, especially with thin metal. That would leave you with an ever-sagging trough as traffic stretches it out.

You also don't use caulk, foam, or any other soft material as sheet vinyl flooring requires a hard, flat, stable substrate or you'll see the depression telegraph through over time.

I would probably use a vinyl concrete patch, though it's important that it be a product designed for gaps that wide. Some materials shrink too much.

You could also use masonry mortar and then skim with a finish coat of leveler designed for vinyl floors.

  • 2
    That looks like it's a really deep crack you're trying to fill. I'd suggest putting some backer rod (basically round foam strips) into the crack a couple inches down to seal the bottom of the crack so you're not needing a huge quantity of fill material.
    – Milwrdfan
    Sep 21 at 21:31
  • 1
    Mortar shouldn't be so loose that it flows into the crack. Once it's a few inches deep it'll hang just fine.
    – isherwood
    Sep 21 at 21:32
  • Yeah the gap is extremely deep, ok so some kind of backer rod to keep the vinyl concrete patch in place sounds like the best option. Massively appreciate everyone’s help with this. Will give this a try tomorrow and if no good, I’ll potentially have to think about a tile floor or Laminate floor instead to cover the gap!
    – David
    Sep 21 at 21:48

If I understand the picture right, all you need is to fill this up with either foam and/or caulk, since you will presumably have a threshold installed under the door. Whatever you decide to use (foam or caulk), insert a backer rod first, so that the material does not fall down.

  • The threshold won’t actually cover the gap due to the placement of the gap, so I would need to fill the hole.
    – David
    Sep 22 at 10:47
  • 1
    I don't understand the picture then. If the two floors are at the same level, you can add a backer rod and then some caulk/foam and just add flooring over it. If the floors are at different levels you'll have to have a transition, ie a threshold wide enough to cover it.
    – Cheery
    Sep 22 at 10:50
  • Caulk or foam will not properly support sheet vinyl flooring, which needs a hard, flat substrate.
    – isherwood
    Sep 22 at 12:43
  • 1
    Yeah, "cover it with the door threshold" was exactly what I was thinking until I looked again. The door is already installed and the frame is completely on the concrete and doesn't bridge to the wood. If it did, that would have been the ideal solution. :(
    – FreeMan
    Sep 22 at 13:12
  • There will be no threshold. This is an interior door.
    – isherwood
    Sep 22 at 13:32

I would suggest using a construction sealant, specifically Sika brand. It’s super stick yet will remain flexible forever. I would not suggest any of the concrete patch products because their self leveling makes them run away on anything vertical. Don’t substitute. You can foam back it if you need to

  • 1
    Flexible is a bad property under sheet vinyl flooring. Most concrete patch materials are not self-leveling unless you overwater the mix.
    – isherwood
    Sep 22 at 12:43
  • Im talking about filling a smallish gap with construction sealant that bridges between two different foundations that were built like that for some reason. Has nothing to do with concrete patch work. Flexible adherence between the two seems important and i don’t what flooring likes it or not, if you’re laying anything down you should have the proper underlayment that would keep anything from touching my caulk. Sep 24 at 19:55

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