I. What is Efflorescence?

Have you ever noticed white deposits on the wall and floor surfaces of your tile or stone installations?  This white residue is the result of efflorescence.  Efflorescence is a natural occurrence in Portland cement applications.  All Portland-cement based products, which are present in render and screed mortars and most cementitious adhesives, will have this presence of calcium hydroxide crystals after the hydration process.  Efflorescence usually arises from the percolation of water through the cement-based backing that leaches out soluble salts, which are then deposited on the surface through the joints.  The leached lime, when exposed to the atmosphere, will react with carbon dioxide to form calcium hydroxide crystals.
To put it simply, the presence of water, travelled through a water path in contact with the calcium salts present in cement-based products, is drawn out to the surface through the capillary pores of the cementitious tile grout. Once the water evaporates, it leaves behind a white residue.  Efflorescence is harmless, but unsightly, and can occur on both vertical and horizontal surfaces. 

II. What causes Efflorescence?

A combination of three factors cause efflorescence:

• Soluble salts present in cementitious mortars, i.e., leveling mortars, adhesive bed and tile grouts.
• Water.
• Water path (passage for water to travel)

Typical site conditions that can trigger efflorescence:

• Excessive damp and humid environments (water feature, swimming pool).
• Use of excessive water and methods in wiping off surplus grout when cleaning tile joints.
• Outdoor areas that are exposed to rain and potential water elements and are not protected.
• Prolonged delay in drying out after complete tile installation.
• Joints are too narrow and difficult to properly fill it with grout mortar.

III. Preventive measures:

To totally eliminate efflorescence in the tiling system, tile/stone installations should be free of cementitious mortars.  However, it is not always possible as cement-based products are normally needed for levelling beds (i.e. renders and screeds). 

Hence, it would be better to eliminate any one of the above three conditions to prevent efflorescence.  Let’s take a look at the preventive measures:

• For external flooring applications, it is important to ensure that the tile joints are filled as soon as possible during works in progress. Otherwise, provide “shelter” to protect the “open” joints from rain and water after the tiles have been laid

• Incorporate a waterproofing barrier (e.g. flexible cementitious waterproofing mortar) over the entire levelling beds before laying tile with tile adhesive.
• Use epoxy or polyurethane-based adhesives to install tile/stone. If it is not possible, an alternative is to use fast-setting cementitious adhesives. Mapei’s Granirapid and Elastorapid cement-based adhesives contain lower content of Portland-cement in its formulation.
• Allowing the substrate to cure completely and dry out before proceeding with tile installation.
• Incorporate a wider joint gap between tiles so that joints can be properly grouted to sufficient depth (check out our video guide on installing tile grout).

When efflorescence has already occurred, it would require repeated washing until the calcium salt is depleted.