Managing the risks of efflorescence

July 6, 2019

By Michael Micalizzi, CTC

All photos courtesy Custom Building Products[1]
All photos courtesy Custom Building Products

The costs of cleaning efflorescence from grout joints and tile surfaces can range from a lost day on a callback to a fortune, depending on the size and type of project on which it occurs. For example, to acid-wash tile on one large project, remediation costs exceeded $100,000 for labour and scaffolding. Additionally, the owners were highly concerned with acid-wash residues over window trims and plantings because the cleaners used to remove efflorescence are acidic and could damage plantings and leave residue. Further, the metals on the exterior were a primary concern due to the acids. The owners also expressed fears regarding risk to occupants entering and leaving the building.

Figure 1: Placement of a drainage mat in a tile/stone assembly aids in water evacuation.[2]
Figure 1: Placement of a drainage mat in a tile/stone assembly aids in water evacuation.

Often, these issues with efflorescence lead to hiring consultants and attorneys. In these disputes, the general contractor (GC) and tile contractor will not accept responsibility for efflorescence as the design team approved the installation products and configured the building components, such as drip edges, that may have led to the problems. Manufacturers disclaim the occurrences unless materials that will not contribute to it are used. In this actual event, the contractor substituted a lower-grade grout when the specified one was not readily available. He denied, it of course, but laboratory analysis was able to reveal the substitution.

Efflorescence occurs when mineral salt deposits that have leached or migrated from cement and masonry materials are carried to the building’s surface in moisture vapour. These minerals occur naturally in Portland cement and, when dried, appear as a white film, powder, or crystal. Many kinds of mineral salts have been detected in multiple samples of efflorescence, including sodium sulphate, potassium sulphate, sodium carbonate, calcium sulphate, sodium bicarbonate, and calcium carbonate.

Efflorescence from minerals in natural stone.[3]
Efflorescence from minerals in natural stone.

The tile industry has experienced efflorescence for a very long time. Unfortunately, building owners and GCs often believe it is solely the tile contractor or installation material supplier’s responsibility to prevent it from happening, and remove it when it occurs. Although poor installation methods can cause it and certain products are more susceptible to it, in many cases, building design and product selection causes or contributes to the problem in both interior and exterior applications.

New concrete and mortar beds provide a source for efflorescence in a wide variety of projects. For example, when porcelain tiles are installed in exterior applications, the mortars used are polymer-modified, so when standard-setting, Portland cement-based mortars are used instead of rapid-curing, calcium aluminate-based types, they retain moisture for an extended time, adding to the possibility of salt migration. Note, standard-setting and rapid-setting mortars are both polymer modified, however, the cements used in the two are different. Calcium aluminates are preferred as they set faster, and contain very little sources of minerals that effloresce, like lime.

To prevent the issue of salt migration, it is important to address the main causes resulting in or contributing to efflorescence, namely:

Design/construction professionals will likely be familiar with many of these issues, but unfamiliar problems may catch a team by surprise.

Tile installation practices

Efflorescence caused by poor mortar coverage.[4]
Efflorescence caused by poor mortar coverage.

A contractor’s proper, moderate, and controlled use of water during an installation is critical to lessen the risk of efflorescence. Over-watering grout (i.e. using too much water to finish grout), and leaving excess water on the tile or grout surface can result in a light residue or substantial blooms of efflorescence.

Efflorescence forms due to soluble salts within a concrete substrate, a mortar bed, installation materials, and/or grouts. When water acts as a carrier of the salts through grout, they dry and crystallize on the tile surface as they are exposed to air. Even some tiles and natural stone varieties (typically cement and sedimentary stones such as limestone) can effloresce when exposed to water. Excessive use of water can easily start the reaction, especially when site conditions are cold or humid, or when heat draws moisture from a damp substrate or tile assembly.

Mortar manufacturers recommend an acceptable water range for mixing and recommend waiting until grout gels or firms before finishing. Otherwise, the unreacted grout will be damaged. Washing should always be done with a damp sponge, not a wet or soaked one that may flood the joint and leave puddles.

Figure 2: The effects of reducing slope in a tile assembly with allowable installation variables are explained in this chart.[5]
Figure 2: The effects of reducing slope in a tile assembly with allowable installation variables are explained in this chart.

Mortar coverage of less than 95 per cent under a tile or stone in wet areas, in either a vertical or horizontal application, allows water to flow or set on cement adhesives and substrates. As the water evaporates, it allows formation of efflorescence under the tiles (also known as subflorescence or cryptoflorescence), which later finds its way through grout and sealant joints. This cycling effect of efflorescence formation can also contribute to bond failure, as these minerals expand below and around the tile, creating compression at the bond interface and between tiles.

Additional installation errors in flatness and pitch of components in the tile assembly can easily lead to efflorescence. The requirement for proper drainage on horizontal surfaces in wet areas is 6 mm (¼ in.) in 300 mm (12 in.) per linear foot. This requires preparation work to the substrate (pre-slope), the mortar bed, and the waterproofing or crack isolation membrane. The tile or stone must also be in plane with the pitch. Slight birdbaths in the substrate, mortar bed, or tile lippage will slow or prevent water from draining, resulting in concentrations of salts and efflorescence. Often overlooked is the need for grout to be consistent in depth and smoothness and as close to the tile surface as possible.

Other related components of a tile assembly, such as a floor drain, must have effective weep holes and proper tile edge heights around them for water drainage. When sealant or grout is very low around the drain flange, water evacuation is slower than the time it takes to dry, and efflorescence forms in these areas. Sealant in other movement joints can also be problematic if not properly detailed with sufficient product forced into the joint to adhere to the tile edges or placed over backer rod per Adhesive and Sealant Council (ASC) recommendations. Since these joints begin either below the concrete or at the substrate level, they are typically a faster pathway to the surface for efflorescence.

Installation materials

Figure 3: Proper flashing using a drip edge.[6]
Figure 3: Proper flashing using a drip edge.

Portland cement products naturally contain lime, which is a source of the salts that migrate to the tile surface. Practically every installation material manufacturer disclaims liability for efflorescence formation with Portland cement products for this reason. Concrete, plasters, mortar beds, dry-set mortars (thin-sets), grouts, and some tiles are manufactured with Portland cements. So, efflorescence is difficult to avoid, but it can be controlled. There are alternative products available that greatly lower the possibility and eliminate some of the sources of these salts. When such products are used as a system, the risk of efflorescence is very low.

Efflorescence from concrete substrate.[7]
Efflorescence from concrete substrate.

The first step is to include a flat membrane (such as a liquid- or sheet-applied type) able to restrict water from entering the substrate. Concrete and other cement substrates are the most likely culprits to provide a source for efflorescence in an assembly, so use of flat drainage membranes can significantly reduce the risk of this problem. Due to their geometric cavities, uncoupling mats may also trap or slow water from draining and result in efflorescence. Drainage mats are perforated to allow water to pass through them, but typical uncoupling mats are not. A drainage mat creates space under a mortar bed with its egg carton configuration. However, a cleavage membrane is in 100 per cent contact with the mortar bed and substrate so water slowly drains from the assembly. In this time, freeze/thaw effects are more likely to occur and cause heaving and efflorescence. Adding a drainage mat under a mortar bed in exterior applications instead of using a cleavage membrane will be a great help to move water to a membrane and out of the assembly (Figure 1).

Second, mortars and grouts made with calcium aluminate (CA) cements or blends of primarily CA are much less likely to contribute to efflorescence, as these cements contain little or no lime. These product formulations are exothermic and cure quickly, using up water at a faster rate. Many manufacturers advertise CA cements will not contribute to efflorescence or effloresce at all. This is especially important in cold and damp conditions. Premixed or single-component grouts and epoxy grouts are another option, as they are noncementitious, typically free of efflorescence-contributing materials, and warranted to be so.

To help prevent minerals from migrating out from cement-based tiles or natural stone, penetrating sealers might be a solution. To adequately accomplish this, a ‘six-sided’ sealing process is employed, in which the cement-based tile or stone is immersed in penetrating sealers, and, after removal, are allowed to dry until the next day. Some penetrating sealers will allow adhesion with cement mortar. It is important to note, not all sealers, even penetrating types, are acceptable.

Project design options and flaws

Standing water results in efflorescence.[8]
Standing water results in efflorescence.

Numerous design choices can lead to the formation of efflorescence. One of the most common is reducing the substrate and assembly pitch from 6 mm in 300 mm per foot to 3 mm (1/8 in.) in 300 mm per foot. This is often proposed with accessible showers and exterior decks/balconies where the elevations have not been properly accounted for or the design team feels the pitch is too severe. As shown in Figure 2, this reduction severely impacts the margin of error for even the best tile contractor due to acceptable variances in the installation and the tile itself. The actual pitch could be reduced to 0.7 mm (1/32 in.). Figure 2 also shows allowable variances in the tile manufacturing, lippage tolerance during installation, grout (no standard for depths), etc. What makes things worse is the tile and natural stone recommended for these areas are purposely profiled, rough, or clefted to provide adequate slip resistance. That also means they will slightly slow down water flow or prevent water from draining, resulting in ponding and formation of salt deposits.

It is crucial to take steps to prevent efflorescence.[9]
It is crucial to take steps to prevent efflorescence.

Construction schedules and budgets all too often push the limits on risks with regard to surface preparation, curing timeframes, or costs to add products that would manage efflorescence and avoid potential failures. Not correcting variations in substrate pitch to effectively evacuate water, not providing protection from the elements until the installation products are cured, and filling pools and water features too soon are just a few examples of real life conditions. Additionally, rapid-setting mortars and cement grouts or noncementitious grouts and waterproofing membranes used in a system may be more expensive, but can limit risk of efflorescence. In the author’s experience, waterproofing or moisture mitigation is often ‘value engineered’ out of the specification, proper sloping is eliminated, or tile is direct bonded over fresh concrete. Most tile contractors have been told at one time or another,
“I need it installed now! Just put it in or I will have to get someone else.” In such situations, the possibility of efflorescence is not considered.

Efflorescence from minerals in natural stone.[10]
Efflorescence from minerals in natural stone.

Exterior tile roofing and façades require a design able to effectively evacuate or shed water. Another common flaw is poor detailing of drip edges or the elimination of them altogether at a rooftop or around windows. When water is allowed to seep behind a tile, it will eventually find a way out, bringing with it minerals and salts. An extended drip edge and gutter will help keep water off the sides of the building (Figure 3). Also, at times, a stone façade is chosen that does not allow for grout in the joints. It can be expected efflorescence can occur in this design, as water is freely allowed into the bonding mortar and substrate, allowing easier salt migration.

Proper design of movement joints in every assembly relieves the stresses of normal building movement from deflection, loads, and thermal changes. When expansion joints are inadequate, tile expansion and the resulting compression of joints cracks grout or loosens tile, creating fissures for water and moisture to pass through and draw out minerals from below. It should also be noted, dark-coloured tiles absorb and retain much more heat, a factor leading to increased expansion and fractured grout without adequate movement space.

Rising moisture brings minerals to the tile and grout surface.[11]
Rising moisture brings minerals to the tile and grout surface.

Irrigation systems have also been known to create cycles where the assembly is saturated and dries repeatedly. Typically, sprinklers supply water in the early morning, and as the sun rises, heat draws out moisture from grout lines along with minerals and salts. Improper grading also impacts water flow. Worse, some water used for irrigation could have greater potential to cause efflorescence if it is reclaimed and rich in minerals.

Since anyone’s actions on a project could cause the appearance of efflorescence, it should be an important consideration for every installation. Each person involved should reflect on what steps can be taken to manage risks. Important strategies include performing a mockup to evaluate the details related to the potential for future efflorescence, such as pitch or the reaction of a standard grout over a fresh mortar bed, along with incorporating industry best practices, such as creating adequate substrate and waterproofing pitch, edge detailing, and acceptable adhesive mortar coverage. Not to be overlooked is heating or tenting the installation in extreme temperatures and providing protection from weather during curing. The material supplier will also have suggestions and warranty requirements for the product and assembly installation conditions and protection.

When working on a fast-track project or noticing anything that could cause a problem, one should notify the whole team of the possible risks and determine who is responsible for the remediation.

In the words of former U.S. general Colin Powell, “There are no secrets to success. It is the result of preparation, hard work, and learning from failure.”

[12]Michael Micalizzi, CTC, is the senior director of technical services for Custom Building Products, with more than 33 years of industry experience. In his role, Micalizzi assists industry professionals with recommendations on commercial projects for various installation challenges. Prior to becoming involved in product technology, Micalizzi owned a tile and stone installation company in New Haven, Conn. He currently serves on technical committees for the Tile Council of North America (TCNA), American National Standards Institute (ANSI), ASTM International Materials & Methods Standards Association (MMSA), National Tile Contractors Association (NTCA), and Natural Stone Institute (NSI). Micalizzi can be reached easily via e-mail at[13].

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