Trying to figure out what might have cracked our tiled floor

cdnNick

We moved into our current house (17 years old) about 2.5 years ago and when we bought the house the tiled floor in the foyer and powder room was already cracked, it's about 6 feet long so it goes across multiple tiles in the middle of the room and then again near the toilet, it's a small hairline crack. Our home inspector said the floor looked structurally sound but he wasn't sure why the tiles cracked. This part of the house is above the unfinished part of the basement so I have access to everything from underneath the floor, the joists are 24" OC, I can see the OSB subfloor and I don't see any sagging.

About a month ago the bathroom door started hitting the floor as a few tiles seem to be raised up, if I stand near the bump my weight pushes the tiles down enough that the door doesn't hit them. Since we have these two issues and the connected laundry room has a vinyl floor my wife decided she wants to re-tile the whole area, at this point I want to start to figure out a game plan to correct the issue and hopefully determine what the problem is and if it's something I feel comfortable doing myself.

At this point I am thinking the subfloor isn't thick enough to support the weight of the floor, as it appears the joists are still level. Is there anything I can look for without removing the tiles to maybe help determine the cause of the problem? This is the original builders floor.

Thanks in advance for any help.

hammerlane

Appears that something is flexing enough to break the tiles. Possibly the subfloor or joists.

Do you know if the tile was laid on cement board which was laid into a bed of mortar or just on the plywood subfloor?

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GBrackins

what size are the floor joists, and what is their span?

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Gary

"You get what you pay for, and sometimes free costs more!"

wkearney99

Does the cracking roughly follow the direction of the joists? Or does it run across the direction of the joists? I'm guessing it runs along in the same direction?

You wouldn't see sagging, as it doesn't take more than a few millimeters of movement to cause tile to crack. If you saw actual sagging you'd have seen a LOT more cracking.

The fact that you can change the height of the tiles by standing in the area tells me there's not enough support under there. You should not be able to do that.

It might be as simple as putting new joists alongside the existing ones. They call this 'sistering' the joists. The idea thing is to get the ends of them resting on something secure, either the same ledge as the existing joists or new supports appropriate for the structure. You attach the sistered joists right onto the existing ones, with construction adhesive and proper screws. It would probably be smart to contract with a civil engineer to have them tell you exactly what's necessary to handle the loads you want carried.

24" OC is a pretty wide gap. I don't know canadian code requirements but here in the US we generally use 16" OC. The wider you space the joists, the more movement you risk. Couple that with the dimensions of the joists themselves and you get the problems you see now.

GBrackins

floors typically require a deflection limit of L/360 (where L = length of joists in inches). I was taught that when you have floor joists at 24" o.c. you needed to install another layer of subfloor to provide the L/360 in-between the joists. depending on the type of tile to be installed may require less deflection limits according to industry standards.

this is an informative article http://www.structural101.com/Wood-Fr...-Flooring.html

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Gary

"You get what you pay for, and sometimes free costs more!"

cdnNick

Sadly, I can't tell unless I rip up some of the flooring. I doubt there is cement board since this was done by the builder.

I will measure all this when I get home and post it.

They run the same direction as the joists. The joists run from the foundation wall to a steel beam in the middle of the house which runs the length of the house.

The bump roughly falls between two joists. I'd have to do some measuring to figure out if the crack is on top of a joist or in between them.

GBrackins

if the cracking is running parallel to the floor joists then I would speculate the cracks are in between the floor joists. Probably culprit is excessive deflection of the subfloor. When you get a chance read the article I linked above.

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Gary

"You get what you pay for, and sometimes free costs more!"

cdnNick

The joists are 9.5" wood I beam and the span to the steel I beam is about 11', the joists run the full width of the house. The shorter span in on the side with the tiles. The OSB I can see from the bottom is 3/4" T&G.

Thanks for the link, I read the article.

firehawkmph

Nick,
in addition to what the others said, you may be able to see if there is anything between your subfloor and tile if you have a heat register in the floor or up against the base. Take it off and you see the cut edge of the subfloor, tile and if anything is in between.
Mike Hawkins

cleveman

Wow, you are really screwed if you can move the floor when you step on it. You are either severely overweight, or you have a sheit floor.

Are you able to hold the builder responsible?

Floor joists 24" oc? Obviously it is done, but I guess you can see the results.

Fairview

Tile floors are often cracked by moving appliances with dolly trucks that don't have appropriate pneumatic tires for the load. Even on concrete floors where a poor concrete job in conjunction with an equally poor tile set it can happen. Don't even consider letting anyone move appliances with hard solid rubber dolly tires on tile or even vinyl for that matter.

cdnNick

I don't know why I didn't think of removing the heat register, there is 3/4" plywood on top of the OSB then mortar and tiles. There is nothing in between the sheets of wood and judging by some of the nails that have gone through the subfloor I would say they are nailed together and not screwed down. House was built in 1996 so the builder is out.

cleveman

You will have to do some research to see what is necessary to tile that floor.

1. The type of floor joist and spacing.
2. 3/4" osb
3. 3/4" plywood
4. How is the osb fastened to the floor joists?
5. How is the plywood fastened to the osb?

I have installed a lot of tile on 16 oc dimensional lumber joists with 3/4 osb and then 1/2 tilebacker.

My gut feeling is that your floor could be fine if the osb is fastened to the joists with adhesive and ring shank nails, and the plywood is fastened likewise. But you are still missing the tilebacker with the layer of mortar.

It is acceptable to tile directly on plywood also, and you can look into the requirements for that.

But something is still wrong if you are able to walk on the floor and it flexes. That can never be right. You can't make that right by putting some tilebacker on top of it.

cdnNick

That's the part that worries me, I can't feel it flexing nor can I see it move, the only way to tell is that the door doesn't scrap the top of the tile so it's not moving much. Surprisingly, the tile in that location isn't cracked.

wkearney99

You still haven't said if the cracking is following a particular direction, one that goes with or against the joist direction.

As for not cracking at a given spot, that's not a surprise especially if it means there's a whole panel that's moving. Then you'd only be seeing cracks at that panel's edge, or close to it. Not over at an outside edge where the whole panel is lifting.

I'm still inclined to think there's just not enough support under the area to handle the deflection being caused.

Here's a thought, find out if there's bowing or sagging by checking the underside for level. One way to do this is find or make a level surface under a length of the joists. Then measure down from the joists to that level surface. I say find/make a level surface because the floor itself might not be level. You can lay a level across it to check, but if it's sloped for drainage then you'll have to make a level surface. Just be sure to be using a level that's at least 3' long, not just a small torpedo level from a toolbox. Once you have a known flat surface you can measure from that up to the joists. If you've got, or know someone that's got, a laser level that would make it easier too. The point here is that can help you determine just how much the structure is out of level. That may also help shed light on how the structure has settled and point out where the problems lie.