Effloresence and Tile Installation Systems

Both a lightening of the grout surface and an excessive salt build up 

is shown, when compared to the grouts original colour shown in

 cross section. Primarily the result of excess mixing water.

Secondary efflorescence emanating from the tiling bed of
the stairs as a result of water infiltration at a higher level.

Article written by: Fred Gray, LATICRETE Technical Service Manager

Efflorescence is a process resulting in an undesirable, whitish discolouration (staining) or white salt deposit on a tiled surface from the crystallisation process of soluble salts. 

Crypto (hidden) florescence is a process resulting in the crystallisation of soluble salts in or on the bedding layer of a tile installation.

The occurrence of salt deposits, generally referred to as efflorescence, is a potential problem whenever, amongst other reasons, Portland cement products are used in tiling systems. It is important to note that efflorescence is not considered a defect of the installation materials, but rather a naturally occurring characteristic of Portland cement-based tile installation products. The best way to prevent efflorescence is to better understand what it is and how it happens. Three things have to happen for efflorescence to become a problem:

1. There must be soluble salts (solute) present. These salts are mainly present in Portland cement products from the manufacturing or hydration process. There are however other sources of salts (contaminated sea salt, contaminated mixing water, cement accelerators, acid residues, lime etc…) though.

2. Water (solvent) must be present in the bedding mortar bed and/or grout that will eventually evaporate during the setting process.

3. Some type of force (evaporation, gravity, capillary movement, hydrostatic pressure etc...) has to bring the dissolved salts (solutions) to the surface of the installation.

If all 3 things occur and the water evaporates, salt crystals form and generally remain on the surface where they react with carbon dioxide in the atmosphere. The reaction with carbon dioxide can turn the salts into more difficult to remove solids over time. These salts can be calcium carbonate, sodium carbonate, potassium carbonate, or calcium hydroxide depending on the source of the Portland cement raw materials and any additives that may have been added to the concrete, mortar or adhesive.

Eliminating any of the 3 needed circumstances will help eliminate the occurrence of efflorescence. 

 Efflorescence is categorised as Primary or Secondary;

1. Primary efflorescence generally refers to the efflorescence emanating from the drying of tile installation products containing Portland cement and the mixing water required for the installation process. The formation of efflorescence may also be exacerbated by wet site conditions and temporary background moisture. An example would be the lightening in colour or staining of the surface of cement grout joints after the initial drying period. The drying process brings soluble salts to the surface, mainly light-coloured calcium hydroxide, that may dilute the richness of the intended grout colour or leave heavier salt deposits. Under the right conditions, efflorescence may manifest as a furry, white crystalline surface growth that can be easily removed immediately after its occurrence. Primary efflorescence is considered an aesthetic defect however persistent water infiltration into setting/background/adjacent materials containing soluble salts may result in a functional defect.

2. Secondary efflorescence refers to the efflorescence emanating from the tile installation materials, background materials and/or other sources of solutes adjacent tile installation, where persistent infiltrations of water are present and resulting salt deposits occur on or under tile surfaces after the tile installation has cured. Afflictions range from minor grout staining to glacial, calcareous growths that can require mechanical processes to remove. Crypto florescence is normally associated with secondary efflorescence and has the potential to cause bond failure due to; depletion of calcium in bedding materials; or expansive build ups under the tile system. The severity of these more chronic afflictions is generally related to design and incompatible work practices.

 Ways to help “minimise” the occurrence of efflorescence include:

1. Follow good design principles that target the elimination of any of the 3 factors that are required for efflorescence to occur.

2. Use installation materials that have minimal minerals or salts that can be dissolved and transported within the tiling installation. The use of epoxy fixing materials are a good example.

3. Use the specified amount of mixing water with tile installation materials.

4. Ensure substrates are dry and not subject to constant or intermittent damp before commencing the work. Protect the works from environmental or site water during the works.

5. Use waterproof membranes, to falls, as high as possible in the tiling system to isolate bedding that may be the source of minerals or salts. Don’t allow porous bedding materials to sponge up and hold water in substrate depressions or sump like conditions.

6. Target 100% adhesive coverage and bedding of finish to eliminate voids and tracks that allow water to collect and travel in.

7. Use under bed drainage systems to eliminate water where possible.

8. Limiting the exposure of tile perimeters to infiltrating water. Make use of perimeter barriers and flashings.

9. Slope the area to drain water from the surface to outlets. Water allowed to sit on tiled surfaces are prone to be absorbed into bedding layers through the grout joints.

10. The use of latex and consolidating additives in mortar beds may help minimize the effects of efflorescence by restricting water absorption and the rate of transpiration of moisture through bedding materials.

Unfortunately, at this point, there is no clear-cut answer for the total elimination of efflorescence.

Contact LATICRETE for technical support - call 1800 331 012 or email sales@laticrete.com.au