Why Tile Grout Sweats

Nature of Cement

• Cement as a building product contains a lot of moisture inherent in the mixture. Moisture is also recommended as part of the overall curing process, with concrete blankets being used in most cases to keep moisture in during the curing phase. Afterwards, concrete acts very much like a human body in that it breathes air, and consequently moisture. It not only takes it in, but also sweats or releases it.

Humidity

• If you live in an area that has a high level of humidity, you will notice sweating on your tile or grout. This is because the cement within the grout naturally draws in the moisture from the surrounding air. On concrete slabs, this is evident in the early mornings as they will have a fine layer of moisture on top of them, just like grass does from dew. Grout will do the same thing in extreme humidity, although it will usually only sweat in patches.

Surrounding Soil

• Moisture in the surrounding soil will also make grout sweat if it is contact with a concrete slab that is touching the earth. The concrete will draw in the moisture from the ground, transfer that up through the slab, sweat it out into the thinset mortar, which in turn transfers that moisture to the grout joints where it finally finds release. This is a natural part of concrete and grout installations in areas where damp dirt is a reality.

Counteracting

• The easiest way of prevent sweating grout is to use a moisture barrier when installing the tile on any surface. This moisture barrier goes behind the concrete board or on top of the concrete slab, depending on your installation. The barrier keeps the moisture from transferring up into the grout, which keeps your grout joints from soaking up too much moisture.