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iLiConsult (Civil/Environmental) (OP)
16 Jan 09 22:51
Has anybody seen ceramic floor tiles lifting off suddenly and got a good explaination for it?
The tiles are (were) directly mortared to a reinforced concrete slab. The lifting of tiles occured suddenly and created quite some noise. Apparently, the tile floor was under lateral stress and the tiles had no other way to go than up. There are no signs of structural failure, or settlement of any part of the building.
msquared48 (Structural)
16 Jan 09 23:42
Shrinkage of the concrete slab?

Mike McCann
MMC Engineering

iLiConsult (Civil/Environmental) (OP)
17 Jan 09 0:38
Yes. I suspect shrinkage of the concrete slab. However, the building(s) are several years old.
We are talking about Cambodia which enjoys tropical climate with temperatures around 30 deg. Celsius year around. Night time temperatures drop sometimes below 20 deg. in January. There is a considerable change in humidity between dry and rainy season.
The type of ceramic floor tile failure seems to be a common problem in Cambodia. We have heard and seen it in several buildings over the last couple of years. All incidences had thinks in common.
- All buildings are reinforced concrete structures with floor tiles mortared directly to the concrete slab.
- Most buildings were 2 two 8 years old and had the floor tiles since they were completed. One building was 30 years old and had the floor tiles replaced a few years before the lift-off occured.
- All lift-offs occured suddenly in the dry and slightly colder season.
- In none of the cases signs of structural failure were found.

My current theory is that the concrete slab shrinks because of seasonal variation in temperature and humidity. The ceramic tiles have a different coefficient of expansion and shrink less.

At the same time I wonder why I haven't seen or heard about such sudden floor lift-offs in other parts of the world where temperatures vary more than in the tropic.  
Helpful Member!  hokie66 (Structural)
17 Jan 09 2:25
I would guess that the popping of the tiles is because of the type adhesive and grout that was used.  If, as you said, the tiles were placed using mortar, there would be little flexibility.  Tiles should be bonded to concrete substates with tile adhesive, placed with toothed trowels designed for the purpose.  There have to be flexible joints in the grout at intervals.  I don't know why the failure took so long, but think it is related to work practices in your country.
iLiConsult (Civil/Environmental) (OP)
17 Jan 09 4:35
Right. So one can say ceramic tile floors behave different from the concrete slab underneath. If the connection between tiles and concrete slab is rigid stress builds up that leads to the popping up.
What is it that causes the stress (contraction of concrete slab)? Is it temperature or/and moisture content? Could it be that the floor failure happens so late and that builders get away with the wrong work partice most of the time because we have so little variation in temperature here in Cambodia?

I forgot to mention another similarity in all cases we have seen so fare. None of the pop-ups happend on ground floor but on floors above ground floor. The ground floor slab of all buildings was resting on soil fill (no basement).
hokie66 (Structural)
17 Jan 09 7:13
Concrete changes volume due to change in moisture content:  it swells when wet and shrinks when dry.  And suspended floor slabs tend to have greater total length change than slabs on ground because they are not as restrained.  The concrete in slabs on ground also changes volume, but because it is restrained by the ground, it tends to relieve the stress by cracking in a lot of places or moving at joints, so the total movement is a sum of many parts.

Temperature variation also causes the concrete to change volume, so in your case the cool and dry conditions are additive for shrinkage, and the hot and wet conditions are additive for swelling.

Another possibility for your tiling problem is deflection of the suspended slabs.  I would expect tiles near centre span to be more likely to delaminate, as they would be placed in compression by the slab bending.

There is also the possibility the tiles themselves are not dimensionally stable.  Some inferior tiles exhibit growth similar to brick growth and gradually become highly stressed in compression due to this growth.
iLiConsult (Civil/Environmental) (OP)
17 Jan 09 7:28
Many thanks you for your posts.   
DaveAtkins (Structural)
17 Jan 09 9:23
Yes, I dealt with "exploding" ceramic floor tile at a hospital in the United States many years ago.  It turns out the ceramic tile had been installed with no soft control joints.  Clay materials, like ceramic tile, need the ability to expand, because the underlying concrete substrate contracts.

We instructed the hospital to fix the damaged areas, and sawcut control joints throughout.  I haven't heard of the problem occurring again.

DaveAtkins

Ron (Structural)
17 Jan 09 12:52
This is due, as Mike said, primarily to concrete shrinkage.  Assuming these were set on thinset adhesive, the adhesive is not likely the culprit, because of the weaker shear transfer capability.  If a thickset mortar was used, you can get a lot of shrinkage in that to contribute to the problem.

If you geometrically plot the buckling of the tile, you should see that it corresponds, roughly, to the center of a slab area.

Just because the floor is a few years old doesn't prevent this problem from occurring.  The slab shrinks slowly after the initial drying shrinkage.  If the tile is well bonded to the substrate, then compression strain in the tile will take a long time to mobilize and reach a failure point.  The failure will typically happen instantaneously with a lot of noise, since this is a compression failure of a ceramic/cementitious material.  I have seen this same phenomenon many times in tile covered concrete slabs.
jike (Structural)
17 Jan 09 17:33
I have seen this problem with both precast plank floors and conventional reinforced concrete floors in the US. Precasters will often warn you about this problem as they have seen it happen numerous times.

The Ceramic Tile Institute (may not be the exact name)recommends that a slipsheet be installed between the tile and the structural floor. Check the architectural spec to see if this requirement was included in the installation.

It has to do with the long term deflection of the structural system creating compressive load in the tile until it lifts and explodes.  

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