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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. |
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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
