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Unread 04-07-2017, 10:00 AM   #1
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Tile floor sank overnight?

OK, I know this is crazy, but I could swear I had an area of existing tile floor sink literally overnight. I find this hard to believe without some kind of cracking of the tile/grout, but here's the story:

I have a kitchen island on which there was old laminate countertop, and I had it replaced with granite (my quick calc is about 320lbs for the new top spread over about a 7' x 2.8' area- maybe the equivalent of two people standing on the cabinets).

Literally the next morning I noticed the floor sloped a bit toward the island on one side. It COULD always have been like this as the island was preexisting, and the kitchen already had some less than level areas, but I tend to notice these things. The slope is about 1/4" over 3 ft in the worst spot. I can verify it from the unfinished basement underneath as well, where the joists directly under the island are sitting on top of an interior wall, and the joists off to the left of where the island is are almost 1/4" off the top of the interior wall. Again, it may have always been like this but I never noticed it before. The island and the tile floor have been there for years, but now its 300lb. heavier.

However, there's absolutely no cracking of the tile or grout on the floor and it still feels solid when walked on. I'd expect that kind of deflection over such a short time to crack something on the floor or at least make it "loose". Also, I thought that kind of deflection happened over months or years, not hours.

Anyone ever seen this before without damage to tile/grout? Or am I just imagining that this dip in the floor is something new?

Last edited by GVMan; 04-07-2017 at 10:07 AM.
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Unread 04-07-2017, 11:10 AM   #2
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hi GaRman

for something like this to happen the whole area would of had to shift. 1/4 over 3 feet is tilable by tiling standards. anything over 1/16 of an inch in any one foot so 1/4 in that span is easily done.

you said the joist is 1/4 off of the interior wall so im guessing it was always like that. if it aint broke dont worry about it
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Unread 04-07-2017, 11:55 AM   #3
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Yeah, if we ever retile that floor (which is quite large) I assumed I could level that one area easily. I'm just baffled I never noticed it before, and have a hard time believing it just happened when laying down the heavy countertop.
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Unread 04-07-2017, 12:02 PM   #4
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Welcome, GarMan.

Colby, the tile industry standard for flatness calls for no deviation from intended plane of more than 1/4" in ten feet nor 1/16th" in any one foot. A drop of 1/4" in three feet would not meet that standard.

GarMan, I agree that it's more than likely that the situation was pre-existing if you observe no cracking of grout or tile on your floor. It's possible it was just tiled over a less than optimal subfloor to begin with.

An additional 300 pounds on the island should not do what you're suggesting. Even the weight of the granite materials plus the weight of the people who were installing it plus the people who were watching might damage a marginal tile installation over a marginal subfloor, but I think the damage would be visible if that were the case.

If Mrs. GarMan can live with what you've got I'd suggest you do so.

My opinion; worth price charged.

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Unread 04-07-2017, 12:56 PM   #5
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I'm pretty sure the tile is installed over multiple layers of old flooring so yeah, it's less than optimal. The tile doesn't even continue under the cabinets, it butts up against them and is covered by shoe molding. So if the subfloor deflected under the extra weight I'd expect either the grout to crack or the tile to lift up from the subfloor and crack when stepped on, so I guess the floor sag was already there, maybe even there when originally tiled. Odd that I suddenly notice it now as I've stood in front of that island with a cold plenty of times without noticing. My own weirdness I guess.
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Unread 04-07-2017, 03:01 PM   #6
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Large weights can do strange things to structures over time. At one time, I had a waterbed...over several years, I noticed when I was doing some remodeling, that the supposedly, non-loadbearing wall had 'sunk' into the subflooring about 3/4". The wall was parallel to the studs, but near one, and it literally bent the ply subflooring almost into an L-shape from the extended period of trying to hold up that weight from the bed above. This is one reason why you need to consider the overall weight of additions that can easily exceed the original load calculations used for design of the structure...wood does creep under load. Just look at a bookcase that doesn't have mid-span support. After a number of years, it's not at all uncommon for the shelf to take on a significant bow from the load and it doesn't spring back when the load is removed, either. If the shelf can be flipped, you can start to bend it back the other way, but can't do that with the floor!
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