Despite the best efforts of cement manufacturers to minimize water soluble salts in their mortars, many of their products contain enough to cause efflorescence. Also, additional minerals can be present within the water used during installation, which can exacerbate the situation.
These two conditions must be present for efflorescence to occur:
– A source of water soluble salts.
– Moisture (water) moving through the material to carry the salts to the surface.
As moisture is brought to the surface (through vapor transmission or hydrostatic pressure) the water evaporates and leaves the white powder behind – this is efflorescence.
Efflorescence only occurs in a small percentage of installations. You should leave your floor unsealed for as long as possible (at least 14 days) to allow the mortar and grout to fully cure. If efflorescence is going to occur, it will generally do so within this time period. If it does occur, clean the floor thoroughly and allow to fully dry, prior to sealing.
Please note that if you do use a sealer too soon after installation, you can trap moisture within the floor which could lead to efflorescence appearing below the sealer. Because of sealing prematurely, efflorescence may take much longer to appear than 14 days. In this circumstance, it would be necessary for the sealer to be stripped off the tiles first, prior to cleaning and re-sealing, adding several orders of magnitude to the project.
For more information on this subject, click here to see a technical bulletin from Custom Building Products.