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Someone dropped a hard object on the porcelain tile slab floor in our new house, chipping the tile and causing a hairline crack to open that runs to the edge of the tile slab on one side of the chip and about 12" on the other side before closing up. The crack can be felt with a fingertip, implying that stresses within the slab are causing one side to lift slightly. The substrate is Schluter DUTRA-HEAT mat.

The porcelain slab in question is 47" x 110", much too large to replace in its entirety. So I am looking for suggestions on the best adhesive to use to stabilize the crack and prevent it from opening further due to footstep pressure. I asked the tile manufacturer, who suggested an epoxy grout. That is fine for the chip, but the epoxy is much too thick to wick into the hairline crack.

Any input would be much appreciated.

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  • I'm confused. Is the floor area 47x110" or is that the size of a single tile? A 4 foot x 10 foot tile sounds a touch unwieldy to install. If there are multiple tiles covering the floor, how did a single object drop cause a crack on the entire floor?
    – FreeMan
    Commented May 15 at 17:02
  • Being hairline is the problem. Most adhesives for porcelain want to be place at least on one side and then you put the two pieces together.
    – crip659
    Commented May 15 at 17:48
  • Each tile is 47" x 110". And yes they are quite unwieldy. :)
    – sumizome
    Commented May 31 at 17:43

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If you find epoxy grout too thick to wick in, but epoxy has been suggested, then a lower-viscosity epoxy would be a suitable choice. "Marine epoxy" (for building or repairing boats, particularly fiberglass, kevlar, or carbon-fiber ones) is a common low-viscosity epoxy product that's typically available worldwide.

You might want to dam around the crack using layers of masking tape or modeling clay to limit the extent to which epoxy ends up on the surface of the floor, and you'll probably want to scrape or sand the patch level after it cures (full cure may be as much as 72 hours, depending on temperature, though an initial set may be complete by 6-24 hours.) You don't really want a "quick-cure" epoxy for this type of job. It will take time for the epoxy to wick into the crack.

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Not by any means an expert in this area but my feeling is that expecting the crack to become stabilised sufficiently to resist the forces of a full person’s weight at quite some distance is simply not going to work.

I’d exploit the fact that the tile is already moving (implying the adhesive below is already broken) to remove it completely. After that’d clean up the base and then replace it using regular adhesive.

Risk is of course that it doesn’t come away cleanly. Or possibly it would do so, but is simply too heavy for you to manhandle without specialised supports. (Perhaps a window grab will help?)

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  • I agree that full replacement would be the ideal option. The problems with that are: 1) It will take months to get a new slab sent from overseas; 2) the affected piece projects into a doorway, so removing it would require taking off the door jamb, which would in turn likely damage the wallpaper wrapped onto the jamb. So I'm hoping for a material science solution, even an imperfect one.
    – sumizome
    Commented May 15 at 16:03

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