Bulletin #6
Revised May 8, 2014
Efflorescence
Efflorescence is a crystalline deposit that sometimes appears on the surface of grout joints or ceramic tiles or on natural stone tiles as a whitish powder or crust. Chemically, it is most commonly soluble salts (minerals) from a Portland Cement- based material. The "efflorescence" term is often mispronounced as "effervescence" which is associated to bubbling-action of denture cleaner." Efflorescence can appear on the joints or along the edges of the tile shortly after installation is completed or periodically at later dates, depending on the job conditions. Generally, this material is harmless except for its appearance. It is normally a calcium deposit similar to those found on faucet fixtures, hard-water in dishwashers, automatic coffee makers, steam iron or kettles. The appearance of the calcium deposit does not indicate a product defect nor does it necessarily mean that an installation "tear- out" or replacement installation is required. Grout/tile sealer and cleaner manufacturers are familiar with this condition and can easily advise you from their website “help sections” about products they have for removal and minimizing efflorescence conditions. In severe efflorescence cases where there are excessive or thick layers of the precipitate build up, it can be a symptom of a moisture problem where there is a continuous source of moisture migrating to those locations.
A combination of circumstances causes efflorescence. First, there must be soluble salts (minerals) present in the stone, grout joint material, setting bed, or substrate. Second, water must be present to dissolve the salts and carry them to the surface. Third, evaporation must drive the salt solution to migrate to the surface. At the tile surface the water evaporates and the salt precipitates into a solid that crystallizes and expands resulting in efflorescence. Fourth, if there are voids under the tile and there isn't adequate drainage, water or moisture can collect in those voids, which can result in severe efflorescence conditions. Efflorescence problems can occur on exterior veneers where there are excessive voids and that is why industry standards and building codes require substantially full thin-set contact. Efflorescence problems can also occur on exterior floor applications where there are voids within the thin-set mortar and inadequate drainage/slope. If left untreated, the process the leads to efflorescence can cause the surface of a stone to degrade in a condition called spalling. As the salt recrystallizes it expands and can cause some stone surfaces to spall. Geographic areas with high temperatures are more prone to efflorescence as the evaporation cycles are more rapid and last longer due to the higher temperatures and longer warm seasons.
Efflorescence can originate from tap or irrigation water that comes into contact on the surface of the tile or grout. It can be public or well water. The current popular salt water pools can contribute to efflorescence conditions, particularly if natural stone is partially submerged in the pool water or where the salt water is allowed to migrate to adjacent stone applications. Manufactured cement grouts and adhesives do contain some minerals, so having some efflorescence in exterior applications or interior wet applications is not uncommon. With regular maintenance the efflorescence can be easily removed and controlled.
It is important that interior wet applications such as showers and exterior applications are designed and installed correctly to avoid excessive moisture issues. Vapor retarders should be installed under all concrete slabs and continued up along the edge of the slab and footings. Proper grading of the ground to slope away from the slabs and buildings is important, as well as having a proper slope on the substrate surface, prior to applying the waterproof membrane, and at the slab surface to slope to drain at the rate of 1?4” per foot. Weep holes in drains need to be protected to allow for sub-drainage at the membrane level. Trench drains should be installed around the perimeter of slabs as necessary. Drainage systems should be installed to allow the water from rain and maintenance to drain away into irrigation drains. The tile should never be in direct contact with the landscape. There should always be separation between the tile and the grass or soil to prevent moisture from migrating into the tile assembly. Interior showers should be completely waterproofed. Slope to floor drains at both the membrane level and on the tile surface should be 1?4” per foot. Drain weep holes must be protected and kept open to allow water that reaches the membrane to evacuate into the drain. The key to avoiding moisture problems is to manage the water.
It is possible through capillary or “wick” action for this saline solution to move considerable distances. The first three conditions mentioned above must exist in order for efflorescence to take place and if any one of the three is eliminated the problem will not appear. Experience has proved that as time passes the amount of efflorescence diminishes unless there is an external source of salts and water. In other words, when the original amount of salts in the grout, mortar or setting bed is gradually eliminated, the problem disappears. In the ceramic tile trade, the whitish deposit found on the surface of the grout joints or tile edges is usually calcium carbonate. This is a material formed from the calcium hydroxide (soluble salts) in the hydrated Portland cement reacting with carbon dioxide in the air. Sometimes surface discoloration or mottling can be caused by the migration of chloride salts to the surface. Tooling of joints or the addition of calcium chloride admixtures (an accelerator sometimes used in cold temperatures) or poor curing conditions can also cause discoloration.
How to prevent efflorescence:
Eliminating (1) soluble salts in the basic materials, (2) moisture, or (3) passage of moisture through the setting bed or joint (preventing evaporation) will prevent efflorescence. Unwashed sand should never be used in the setting bed or grout joint. Use the recommended amount of clean water (a stiff mix) free from harmful amounts of acids, alkalis, organic material, minerals and salts. Potable drinking water may contain sufficient quantities of minerals and salts to cause the problem. In the winter, deicing equipment with salt or antifreeze material can be a source of the problem. Any lime used in the setting bed should be hydrated, free from calcium sulfate. USING good quality grouts can minimize efflorescence. To eliminate moisture or moisture passage through the setting bed and grout, job conditions such as temperature and humidity should be observed and regulated in order to get adequate hydration of the Portland cement. Waterproof membranes can be applied over the mortar bed to prevent water from migrating up through the tile and grout. Grouting of quarry tiles in high humidity, moist or wet conditions at temperatures with high to low variation in ambient temperature during the initial 72 hours of cure invites trouble. Favorable grout conditions to avoid efflorescence should be above 50?F degrees with a consistent environment temperature of ± 5?F (10?F max. change) for the first 72 hours of new grout installation.
As general rule of practice, allowing 24-48 hours cure time of the tile setting bed (dry-set mortar) before grouting will significantly reduce the occurrence. If colder environmental, lower than normal ambient conditions are encountered, particularly if you are installing a low absorption tile, is 13" x 13" or larger and/or you are using waterproofing/crack isolation membrane(s). In those cases extend cure times to 48+ hours. When grouting takes place too quickly the trapped moisture helps to drive the calcium salt to the surface. Many manufacturers have liquid grout additives to speed the cure in cases were time to cure is at a minimum.
How to correct efflorescence:
Since water is necessary to produce efflorescence, controlling external sources of water can be important to the success of the installation. Normally the only water involved is the water that was added to the mortar setting bed or the grout joint material. However, irrigation water, which could be well water or from other sources that contain high mineral content, when used for sprinklers that overspray on the tile surface or used to wash down tile surfaces, it can be problematic. Particularly if there is not an adequate drainage system in place to control and evacuate the water. Measures to eliminate or reduce this type of unwelcome water will help cure the problem. Some efflorescence can be removed merely by using a stiff bristle brush, either dry or with clean water, followed by clean water flushing or rinsing. On some jobs the white deposit has disappeared in time merely through normal use. An ANSI approved acid like Sulfamic acid properly diluted can remove efflorescence, but it can be misused and create other problems. Manufacturers of cleaners and sealers produce special acid cleaners that are safe to remove efflorescence. Follow the cleaner manufacturer instructions. Proper cleaning techniques are most important in that the tile and grout surface should be well soaked with clean water prior to the application of the cleaner. Clean water soaking or saturating the grout prior to applying the cleaner is the most common and overlooked step that should be followed. Soaking grout is imperative to have successfully removal and quick results. Flushing the tile and grout surface with clean water is essential. It is recommended that a small area be tested first to determine if the selected cleaning method and products will be acceptable. According to ANSI A108.1 — acid cleaning of ceramic tile, if deemed necessary, shall not be done until ten days after the installation has been completed. There are at least two reasons why acid cleaning might be necessary: either to remove efflorescence or else to remove a scum of Portland cement or staining of the tile by grouts and adhesives.
To help prevent the occurrence of efflorescence in grout, prepare the cementitious grout in a stiff mix. Using a minimum amount of water in the grout material is essential, especially for wide joints, and controlling the temperature of the jobsite is important too. The use of Kraft paper spread over a newly grouted floor for final cleanup works well. The Kraft paper is left on the floor for 72 hours to help damp cure the joints. Kraft paper allows slow and even dissipation of moisture while preventing uneven air and heat to effect sporadic areas. “Damp curing” with breathable kraft paper in lieu of polyethylene paper will result in less efflorescence on the cured surface. Plastic sheeting, rosin paper and new paper cause grout discoloration and these materials should not be used for covering the installation.
A slow transmission of the water is desirable to minimize efflorescence in grout. The use of latex additives in lieu of water to mix with the grout will help reduce efflorescence by slowing the transmission of water. Consult your tile latex manufacturer regarding details. Sealing the tile and grout after it has properly cured will also help minimize efflorescence as it impedes the evaporation and moisture migration process, but it needs to be reapplied regularly to be effective.
There are other occurrences on tile and grout installations that are incorrectly identified as "efflorescence" and are not cleanable by using acid cleaning products. These situations include: paint over spray, drywall-gypsum debris, sanding dust/debris, and latex leaching. Dirty foot traffic on grout, protrusion of white tile- setting mortar from beneath the grout, grout residue from contaminated bucket/sponge, premature cleaning, over watered grout and over washed grout surface during the installation procedure can also cause discoloration. Consult your grout and cleaner manufacturers for their recommendations.