This is what I have been able to Google and find out.
One situation that can develop is if tiles are laid onto
concrete before it has had time to completely cure. The general rule of thumb
is to allow one month to cure per 25mm of thickness of the concrete slab. Even
then, the average house slab can take up to two years to completely cure (and
shrink). If this movement is not allowed for by using the correct adhesives and
including expansion joints, something has to give. This is sometimes called
TENTING. There have even been reports of tiles exploding unexpectedly. This is
due to extreme lateral pressures as the walls and floors move in different
directions. Nobody is expecting their tiles to explode!
Generally speaking, "tenting" does not happen
overnight. Usually, it rears its ugly head about six months after the slab is
poured or sometime after seven years. There's always some evidence that there
has been movement in the slab.
Regardless, it's always a good idea to put soft joints in
the installation OR EXPANSION JOINTS.
You don't want to have a soft joint everywhere, just every so often. A
good frequency is to separate the floor into 3 x 3 meters (10' x 10') areas and
do the perimeter of them. You still keep the open space between the walls – do
NOT fill those voids.
In six months, the slab has achieved most of its cure. After
7 or so years of being dry, the slab acts a little differently as far as
expansion rates go.
I'll try to add a little humor into all of this. If you took a 4" thick Christmas fruit
cake and left it in the pan for a few months, the top would likely get very
hard by June. But if you were to cut into it, you might find that there was
moist cake down below...or even in the middle.*
It would only make sense that the tiles coming up are in the
center, since we usually have a
perimeter space. That's where the most stress is without a release.
So, for Guam - - we probably have the following ingredients
that make us even more susceptible to tenting:
1. Lack of initial
building codes and regulations, inspections and overall lack of excellence in
building since a lot of this work was done probably by migrant workers.
2. More than our
share of earthquakes and tremors – at lease 2-3 dozen a year.
3. The change in
temperatures within any 24 hour period.
Most people do not leave their A/C’s on all day while they are at
work. Therefore, units get hot and moist
during the day and start cooling off when people start coming home and
throughout the night.
4. Our massive
amounts of rain and high humidity doesn’t help either.
For more information:
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