Contractor's Guide to Efflorescence

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Efflorescence is a fact of life with most concrete. We are hearing more about efflorescence related issues because of the popularity of stained floors. As the trend to have exposed concrete floors grows, the industry is struggling... See more » Efflorescence is a fact of life with most concrete. We are hearing more about efflorescence related issues because of the popularity of stained floors. As the trend to have exposed concrete floors grows, the industry is struggling with the problem of unsightly efflorescence, especially when it is trapped under a film forming sealer. This is not to say that exterior decorative concrete is immune from efflorescence issues, but problems with interior floors pose a greater challenge and are the focus of this discussion. This article is meant to be a common sense overview of the major efflorescence issues. We will suggest realistic preventative measures to control the conditions that encourage efflorescence and we will offer remedial suggestions. We will offer useful explanations of this complex phenomenon in practical terms without a lengthy detailed chemical analysis. Decorative contractors usually get the first phone call when efflorescence shows up on a stained floor. Many things may have contributed to a particular efflorescence plagued project, the least of which may be the work performed by the stain contractor who in most cases is unaware of the preexisting conditions that caused the efflorescence. Stain contractors, concrete finishers, builders, general contractors, the design community and owners are all affected by issues related to efflorescence. We hope this discussion clarifies some of the issues so that efflorescence is better understood and the appropriate measures are taken to prevent its occurrence. The costs associated with efflorescence prevention are minimal when compared to the cost and inconvenience of the remedies, especially when the space is occupied. Efflorescence in itself is not a health problem although it might indicate moisture levels sufficient to support mold. Efflorescence is not a structural issue. It is an aesthetic issue, an issue we would all like to avoid. Definition of Efflorescence: Efflorescence is the white powdery substance on the surfaces of unsealed concrete and the white blush seen with sealed floors. Efflorescence is caused by vapor migrating through the slab bringing soluble salts to the surface of the concrete. Efflorescence is normally worn off or washed away on unsealed concrete surfaces. In stubborn cases, a mild acid rinse or even a light sandblasting may be necessary. Efflorescence that becomes trapped under sealer is unsightly and is even more conspicuous on darker floors. In worst case scenarios where the vapor cannot pass through the top coat, a urethane and/or an epoxy for instance, hydrostatic pressure can build to create water blisters indicating delamination of the top coat from the concrete. Blistering is rarely seen with acrylics. Acrylic sealers allow the vapor to pass through, but the salt deposits remain behind creating the unsightly blush that prompts owners to call the stain contractor. Contributing Factors: Efflorescence requires the movement of moisture. Without moisture movement there would be no efflorescence on the surface to create the problem. Unfortunately, too many finishers (non-ACI Certified Finishers) routinely introduce large amounts of unnecessary "water of convenience" to the mix in order to facilitate concrete placement. Primary efflorescence is caused by the water in the concrete evaporating from the slab leaving behind the soluble salts on the concrete surface. The fact that these salts are actually more soluble in colder temperatures coupled with increased bleed water in cold weather increases the likelihood of efflorescence showing up after winter concrete placement. Contributing further to efflorescence with cold weather pours is the use of calcium chloride to accelerate the set time. High slump concrete and the addition of calcium chloride are major contributors to efflorescence. Secondary efflorescence is often described as water coming from underneath the slab or water that is introduced from the surface. Likely sources of secondary efflorescence would be a saturated base material, an improperly drained site or excessive amounts of See less »

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cleaning, concrete, concrete floor, efflorescence, floor, flooring, garage

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Contractor's Guide to Efflorescence

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