| Concrete
Curing
How long does concrete
need to cure before tile can be installed?
While this seems like a simple question, in fact many
issues must be considered.
We understand from the PCA (Portland Cement Association)
and the ACI (American Concrete Institute) that many
variables affect the length of time a slab needs to
cure and the length of time during which curling can
be expected. Some of the more common variables are:
1) Cement - water mix ratio
2) Cement - sand ratio
3) Particle size distribution
4) Presence of accelerators
5) Curing compounds
6) Environmental conditions
7) Location of vapor membrane
8) Exposure to water during curing
You can see that it is not possible to definitively
state how long the concrete should cure before tiling.
Although it may not
be possible to say for sure, what is a typical period
for the concrete to cure?
Many people suggest a minimum cure of 28 days under
normal conditions - although, most thinset manufacturers
say you may get away with 14 days using a premium latex
modified thinset. There are risks though to tiling too
soon - as the slab continues to cure, it will continue
to shrink as it hydrates and the excess moisture evaporates.
This places the tile and thinset under compressive stress.
A premium thinset can better accommodate this stress
and compressive force.
What are the benefits
to allowing a sufficient cure time for the concrete?
Clearly, the longer you can wait before tiling, the
less stress that will be applied to the tile by the
concrete. Also, should the concrete crack, the crack
can be treated (with an anti-fracture membrane) before
it is tiled. If curling occurs (and it often does),
the concrete can be ground before it is tiled. Tiling
before the curling occurs can cause undesirable debonding
of the tile and lippage between adjoining tiles.
What if I can't wait 14
to 28 days for the concrete to cure?
If you really can't wait 14 to 28 days, you may want
to consider a vapor equalization membrane. Reportedly,
this membrane isolates the tile layer from the concrete
layer but still allows for the vapor to leave the system.
This is different from a crack isolation layer that
may not allow the "green" concrete to breathe.
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