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Tips for controlling efflorescence in tile and stone installations

April 27, 2021. 3:55 AM

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 called efflorescence.
Efflorescence is a natural occurrence in Portland cement applications. All Portland-cement-based matrices (e.g. concrete sections, cement renders and screeds) contain calcium hydroxide (also known as hydrated lime), a soluble by-product of the cement hydration process. This is the compound that contributes to the high alkalinity of fresh concrete.
Under wet conditions, water penetrates weaknesses in the cement matrix (e.g. cracks, voids, high porosity, joints, etc.) which then dissolve and leach out the calcium hydroxide when dry conditions return. These are deposited on the surface and, on exposure to the atmosphere, they react with carbon dioxide to form calcium carbonate, a practically-insoluble, white crystalline salt. These are the unsightly efflorescence deposits we see on walls, facades and floors, mostly in exterior environments.

Conditions for Efflorescence?

We can see from the above that three conditions are necessary for the occurrence of efflorescence:
i. Substrates with “efflorescence potential” i.e. containing calcium hydroxide and soluble
salts.
ii. Exposure of the substrates to wetting and drying cycles.
iii. Weaknesses which allow the passage of water into and out of these substrates.

Controlling Efflorescence

The measures for controlling and minimising the occurrence of efflorescence lie in examining the three conditions and identifying good practices which can be adopted for eliminating one or more of these conditions. These can then be summarised as a list of good practice do’s for tile and stone installations.

List of Do’s

Repair and seal all defects in the substrate such as cracks and broken parts during surface preparation.
Allowing the substrate to cure completely and dry out before proceeding with tile installation.
Incorporating a waterproofing barrier (e.g. flexible cementitious waterproofing mortar) over the entire levelling bed before laying tiles with a thin-bed tile adhesive. (This layering sequence i.e. installing the waterproofing membrane over the levelling screed/render, stops the passage of water to the substrate where the efflorescence-causing compounds are at their highest concentrations.
For external flooring applications, it is important to ensure that tile joints are filled as soon as possible during works in progress. Otherwise, provide shelter to protect open joints from rain and water after the tiles have been laid.
Incorporate wider joint gaps between tiles which can be properly grouted to sufficient depth (check out our video guide on installing tile grout).
Use epoxy or polyurethane-based adhesives to install tile/stone. If this is not possible, an alternative is to use fast-setting cementitious adhesives. Mapei’s Granirapid and Elastorapid cement-based adhesives are formulated to minimise the production of calcium hydroxide during the hydration reaction.
After they have been drained for maintenance, water-jet the surfaces of pools and water features repeatedly until they are filled again. (Draining pools and leaving them unattended before cleaning creates the conditions for efflorescence to happen as moisture leaches out from saturated pores in the substrate.)