Cracked Tile Floor

[Greatone76]

I recently was called to a situation where cracks were forming in a tile floor. I inspected and found 2x8's at 16" o.c. spanning 11.5'. I"m getting typical TL/240 and LL/360 deflections, so they are coming in at a reasonable place. I was exception to get borderline to over the typical deflection limits, but I'm not. I'm seeing (2) lines of cracking each about 1.5 feet from the center of the span. They are perpendicular to the span of joists. They look very much like excessive deflection minor small cracks. I have done a bit of research and LL/360 is the tile industry standard. I see that other placed like natural stone tile request more. In this case is there anything to report back for a future remediation if the floor is replaced? Am I missing a temperature or other affect that might be causing this. The one thing of note is that I observed that there was no bridging or blocking between joists, so my only recommendation at the moment would be add bridging and blocking at supports. Do you think that would be enough to fix the issue in the future or is the recommendation additional support or joists if they want to use tile in the future and not want it to crack? Any advice is greatly appreciated.

 

[TehMightyEngineer]

Did the tile have any expansion room at the edges? Did the tile appear to be properly installed? Pictures?

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com

 

[msquared48]

Bridging may help, but I would recommend doubling the joists that are there, and going to L/600 for the live load in the future.

Mike McCann, PE, SE (WA)

 

[dhengr]

Greatone76:
Did someone use a two wheel or four wheeled dolly of some sort, with wheels about 3' (2 x 1.5') apart, to move something heavy across that floor? It seem unlikely that normal uniform loading would cause two fairly parallel crack lines across a floor system. Remember, TL/240 and LL/360 are just deflection numbers, shown over the years to provide good results for most tile or stone type flooring materials. They are not magic numbers of perfect protection for all materials or loading conditions. Smaller sized tiles might help. Reducing the joist defection might help, as might increasing the stiffness of the underlayment layers/materials spanning btwn. the joists. Blocking or bridging certainly wouldn’t hurt in improving the deflection characteristics of the floor system. You might ask a tile setting craftsman, would some sort of reinforcement mesh in the thin set layer, or a thicker setting bed help in some way?

 

[KootK]

so my only recommendation at the moment would be add bridging and blocking at supports.

I'd like to see bridging at mid-span so that you'd encourage load sharing between the joists.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[XR250]

I agree with the others - bridging and doubling of the joists should help. 2x8's spanning 11.5' is a pretty crappy floor system in general - worse for tile.
There may also be some sort of installation anomaly that will only be determined after demo

 

[dik]

This may be useful...

http://www.custombuildingproducts.com/media/736045/whitepaper_uncouplingmembrane_wp105.pdf

Dik

 

[Canuck65]

We specify a minimum l/480 for LL deflection for tile floors. In my opinion, l/360 is inadequate based on experience. I think you also need to question whether the floor has ever been loaded to anything near it's full capacity, thus deflected to it's maximum l/360. My point is, that if this was residential, it would not be unheard of that the floor has never been loaded to its full design load capacity. Thus, the tile may have cracked at a much lower load than perhaps assumed.

Adding blocking is a good idea, as is sistering the existing joists. Sometimes I have justified sistering every 2nd joist, plus adding blocking.

 

[MikeHalloran]

Sister the middle half of every joist, then block at midspan and at supports.


Mike Halloran
Pembroke Pines, FL, USA

 

[Greatone76]

Thanks all for your input. There isn't much to see the cracks are hairline and extend 10 in length along the floor. They also show up roughly in the same (2) locations in the tile in the bathroom next to the kitchen. So, I don't believe it is an overloaded with a dolly situation since it is in both rooms at a location not convenient for a dolly. The edges were covered by the usual trim, so not sure about expansion room. I would guess I would have seen more sporadic locations if it expansion rather then perpendicular to the joists at (2) distinct locations. The tile was on 1/4" wish thin set mortar bed and appears to be reasonable from what I could tell. No hollow sounds when tapping. I'm just having a hard time making a statement about the overall condition because the numbers show reasonable acceptability, but the performs lacks. I was expecting to fin LL/240 deflections and have a more cut and dry recommendation to produce.

 

[TehMightyEngineer]

Sometimes saying that it meets the minimum design standards but still failed isn't wrong. They're only minimum standards and you can recommend higher standards if needed; perhaps those two joists have a really low modulus of elasticity? Who knows.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com