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Cracked Subfloor


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  • Cracked Subfloor

    Hi everyone,

    I have a serious problem with my home that has become noticeable within the last couple of years. I have a breakfast nook area connected to the kitchen, and the floor underneath the tile has cracked near the edge of the floor a few inches from where it meets the wall. It is cracked like this along all three walls of the breakfast nook area. This crack creates quite a bit of vertical separation between the two sides of the crack (between 1/4" and 1/2" in places). This vertical separation has popped up the tiles around the edges of the room (which is how I first noticed the problem). I don't seem to have this problem in any other room in the house.

    If anyone could provide some insight into the following questions I have, I would truly appreciate it:
    1. Is this something I could probably fix myself by removing all the tile in the room, paving over the cracked subfloor, and retiling? I don't really have experience with flooring, but I am pretty handy around the house.
    2. Any clues what could be causing this? My only theory is that there is a hose spigot outside on one of the three affected walls, and I've noticed lately that it might be leaking a bit (on the outside - I plan on replacing the spigot this weekend). Could water from the outside be responsible?

    I've attached two pictures: one showing the tile popped up around the edges of the room, and another with a couple of tiles removed, showing the crack.

    Some additional information:
    • The home was built in 1987 and is located in a dry climate (Las Vegas)
    • There is no basement
    • I've owned the home for 3 years
    • I had a home inspection performed when I purchased the home, and they did not see any signs of structural damage
    • I placed some caulk between one section of the crack about 4 months back to see if it ripped (to indicate if the problem is getting worse). It appears unchanged, so my guess is that the crack isn't getting worse.

    Thanks in advance for any help.


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  • #2
    Can you see cracks in the actual concrete slab ? If there are do they travel just inside the wall all the way around ?

    Yes a dripping faucet can most certainly cause foundation and slab issues (usually it's more defined to foundation and appears by way of cracking walls or stucco.
    Little about a lot and a lot about a little.
    Every day is a learning day.


    • #3
      If by "concrete slab" you mean the concrete directly beneath the tile (as shown in the picture), then yes, I see the crack there (as shown) and the crack travels just inside the wall all the way around the three walls of the breakfast nook area. I presume that the concrete I see beneath the tile is the bottom slab, but I don't really know if that's what you're referring to (I don't know much about house foundations).


      • #4
        It looks like from your picture and description that the slab (concrete floor) has dropped is the room side of the crack lower than the wall side of the crack ?
        This can be caused by water issues like a leaking faucet especially in Vegas area soils. Have you looked on the exterior for any obvious cracks ? If you have a level it would be handy to see if the floor slopes towards the exterior walls.

        Obviously the leak needs to be repaired before any other work is performed.

        Once the settling of the concrete slab has been stabilized the cleanup and repair is messy but can be completed by an experienced homeowner. It will mean the removal of tiles and all old glue (mortar), thorough cleaning of the slab surface, installation of a crack isolation membrane that covers the crack, floor leveler (could be a little or a lot depending on the amount of settling) then re tiling the area.

        The crack isolation membrane is the key here, a primer is painted to the concrete surface on both sides of the crack, it is allowed to tack dry then after removing tape off the back of the membrane you press it onto the primed area and over the crack. Floor leveler (if needed), tile glue and tiles are installed over the membrane, the membrane allows movement in the crack without cracking tiles.
        Little about a lot and a lot about a little.
        Every day is a learning day.


        • #5
          That is correct, the room side (the center of the room) has dropped lower than the section around the edge of the room (against the wall). I've looked at the inside and outside wall surfaces for cracks but haven't noticed anything. There are a few patchy sections in the outside stucco where some has rubbed/chipped away, but to me it just looks like normal wear and tear.

          The vertical distance between the two edges of the crack are pretty significant in some places. Do you think I would be better off using a crack sealant like DAP concrete crack sealant, as opposed to a membrane sheet?


          • #6
            If the gap is large 1/8" or more then seal it with a concrete crack sealant just inside the crack, not on the concrete surface. You will have to still use the membrane as what it does is allow future movement (which it will now do as it's cracked) but will isolate that movement and not crack your tiles/grout.
            Joint filler/sealant does not bond the two cracked pieces together, it simply seals the area, so if you add a tile over the crack and it moves again, the tile will break and essentially you will be back to where you are now.

            After the membrane is installed you will have to use floor leveler to bring the slab back to a level area before tiling.
            Little about a lot and a lot about a little.
            Every day is a learning day.


            • #7
              OK, I think I understand. And yes, the gap is larger than 1/8", I believe. Thank you so much for your help!