We have all seen it. That chalky white powdery residue that is evident on newer brick and block masonry projects. Unfortunately, it can also occur on newer stone installations as well. That chalky white powdery residue is called efflorescence.
Efflorescence is a natural occurrence when using cement-based products subject to exterior or wet environments. Efflorescence is crystallization of soluble slats that are carried to the surface of the stone or grout joints. There are three things that need to occur in order for efflorescence to manifest itself.
1. Presence of soluble salts in any of the following:
2. A vehicle to carry the salts to the surface (e.g. moisture flowing through the installation system). This can occur when penetrations and wall caps are not detailed correctly. If moisture can be controlled, even if the salts exist, they may never make it to the surface.
3. A mechanism that can “draw” the salts to the surface. Usually, moisture will travel from cooler environments to warmer environments. This can occur in exterior applications when the sun shines and warms the surface of the stone. The moisture will be drawn to the surface as it carries the soluble salts with it. The salts will then crystallize and be deposited on the surface of the stone or grout joints. This phenomenon can also occur in indoor applications when moisture travels from the cooler areas beneath a concrete slab to the warmer air above the slab. H.V.A.C. systems can also help to draw these salts to the surface. Normal atmospheric humidity and temperature variations can be enough to draw efflorescence to the surface.
Efflorescence is generally a temporary condition that may diminish over time as the soluble salts work their way out of the substrate and setting system. It is important to note that in some cases, this condition could persist. Until then, the efflorescence may be cleaned using a commercial cleaning solution and a stiff bristle brush.
You can contact a manufacturer of these types of products for additional information on their use. It is always a good idea to conduct a test area with the cleaner and the stone to verify results and to ensure that no damage occurs to the stone finish.
There are also many industry-related documents and papers that have been published on this topic. Some of the better ones are published by the Materials and Methods Standards Association (MMSA), the Ceramic Tile Institute of America (CTIOA), the National Tile Contractors Association (NTCA) and the Marble Institute of America (MIA). These organizations publish information on the causes, remedies and means to prevent efflorescence.
As a point of clarification, we want to point out that, at times, efflorescence is misdiagnosed as latex leaching. These are not the same conditions. They are two distinctly different situations caused by two very different sets of circumstances. You can also find information on latex leaching through the same industry organizations listed above.
There are a few things that can be done on a project to help reduce the potential for efflorescence. We mentioned previously that controlling the passage of moisture through the installation is a great way to alleviate this problem. The use of an appropriate waterproofing membrane in wet areas and exterior applications is a great place to start, especially when it comes to exterior stone facade applications. Proper detailing at parapet wall caps, flashing details at penetrations, windows and doors, and the insertion of appropriate weeps also help to reduce infiltration of water and subsequently efflorescence.
The use of good quality installation materials is another way to reduce the potential for this problem. The better the raw materials; the less chance for the presence of soluble salts and other undesirable elements in the installation materials. Factory and quality controlled pre-bagged mortars and additives will always be better than site-mixed mortars in this regard. The use of latex additives for the mortar beds also helps to encapsulate the free salts that may be present in the system.
Lastly, the type of grout used can also affect the amount of efflorescence that occurs. There are new types of grouts that can be used with stone that will not experience all of the typical inherent problems that Portland cement-based grouts do. Some of these products include a unique cross-linking technology grout and various epoxy-based grouts. One of the advantages to the cross-linking technology grout is that it contains no Portland cement, which can lead to efflorescence, mottling and other color problems associated with Portland cement-based grouts. If the cement-based components are taken out of the installation system, then the potential for efflorescence is further reduced. This also applies to the waterproofing membranes and adhesive mortars.
To summarize, the efflorescence problem may never be eliminated. However, it can be controlled and contained, and measures can be taken to drastically reduce the potential for its occurrence. Good installation practices and the use of good quality installation products go a long way to producing a problem-free installation.
Arthur Mintie, CSI