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Efflorescence 101: Causes, Remedies, & Prevention

Concrete coping and efflorescence.

The Basics of Efflorescence

The term efflorescence refers to the unsightly whitish deposit found on the surface of concrete, brickwork, pavers, or other masonry. It develops as mineral salts from inside the substrate are transported to the outside by moisture. It’s not uncommon for efflorescence to grow or bloom, forming fluffy hair-like fibers. The word “efflorescence” actually means “to flower out”, in French.

Efflorescence often becomes trapped below topical sealers (acrylic and urethane topical sealers) and appears as a whitish blush or haze. It’s not uncommon for efflorescence blooms to delaminate sealers and tiles, or cause paints to bubble, crack, and peel. Colored or stained concrete can develop blotchy patches as efflorescence purges color pigments. it is typically white, but can also be yellow or brown, depending on the type(s) of salt present.

In order for efflorescence to form, the following conditions must exist:

  • Soluble salts must be present.
  • Salts must be dissolved by a liquid.
  • The liquid must have a path to migrate to the surface and evaporate.

Cement-based substrates, like concrete, stucco, and mortar contain the highest amount of soluble salts, and therefore produce efflorescence most often. Clay brick, pavers, and low cement CMU’s present a lower risk for efflorescence, as the soluble salt content is lower. Although efflorescence stains on red brick can be quite common, the source of the efflorescence is usually cementitious mortar. Salt-laden water moves from the mortar into the porous brick and evaporates through the brick face, leaving efflorescence on its surface.

Paint peeling  from concrete efflorescence.

Efflorescence releasing the bond of paint off a garage stem wall.

Efflorescence Concrete Floor Basement

Efflorescence bloom on basement concrete floor.

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How To Clean Efflorescence

You’ve got it, now how do you get rid of it? Removing efflorescence from your concrete and masonry typically requires very little besides the right cleaner and some elbow grease.

Traditional efflorescence cleaners promise results, but at what cost. Choking fumes? chemical burns? Damage to your masonry and other materials in the vicinity of your project? Muriatic, hydrochloric, and other “old-school” cleaners are very hard to work with and not suitable for indoor use.

There is a safer alternative. RadonSeal Efflorescence Cleaner packs the power of acid, without the health hazards and logistical inconveniences.

For details on cleaning efflorescence, visit our Efflorescence Cleaner Product Page.

Types of Efflorescence

There are two basic types of efflorescence: Primary and Secondary.

PRIMARY EFFLORESCENCE

Efflorescence is considered “primary” if forms during the initial cure or manufacture of concrete and masonry products. In the case of primary efflorescence, the source of the soluble mineral salt and the water to dissolve and transport the salt originates in the substrate itself. Take for example, a new poured concrete slab. Soluble salts from Portland cement are dissolved and carried to the surface as bleed-water settles upward and eventually evaporates – primary efflorescence is left behind.

Some concrete installers will add excessive amounts of water to concrete for a more pliable product or add calcium chloride to expedite the initial cure. As a result, the risk for efflorescence is significantly increased in these situations, as more salt and more water = more efflorescence.

Primary efflorescence typically corrects itself after a few years. Unfortunately, the whitish deposits are ugly and can cause a significant dust problem. The existence of primary efflorescence can interfere with adhesives and overlays, so it must be removed before painting, installing flooring, or otherwise finishing.

 

SECONDARY EFFLORESCENCE

Secondary Efflorescence refers to efflorescence that develops after the concrete or masonry is cured or formed. Generally caused by water originating from an external source leaching salts to the surface.

Secondary efflorescence is common where hydrostatic pressure is high. When basements, storm cellars, or retaining walls show efflorescence, it is likely due to hydrostatic pressure. As groundwater gathers around your foundation, it exerts pressure against your foundation walls and concrete slab. When the water migrates inward, it carries salts from the soil, as well as salt dissolved from your concrete.

On-grade concrete slabs, walkways, patios, etc. pull moisture from below by capillary action. Wind-driven rain, sprinklers, and frequent wetting and drying cycles are often the cause of efflorescence on walls. Cold and damp areas, like garages, and shady patios and walkways, are more prone to efflorescence – water evaporates more slowly allowing more salts to reach the surface.

While secondary efflorescence can be as aesthetically displeasing as primary efflorescence, it is often considered a symptom of a larger moisture problem, requiring corrective measures.

When Its No Longer Efflorescence

Efflorescence is water-soluble. After all, the salts migrated to the surface by being dissolved by water. One way to identify efflorescence is to put water on it and see if disappears. Although the efflorescence stain is no longer visible, once the water evaporates the salts will once again appear on the surface.

However, over time, efflorescence reacts with carbon dioxide in the air and builds up as a rock-like layer of calcium carbonate (limestone). This is not efflorescence, in the traditional sense. This deposit is very difficult, if not impossible to remove completely. It may require several applications of cleaner, or in severe cases, a grinder, chisel, blasting, or other mechanical means.

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Preventing Efflorescence

Cleaning efflorescence is only the first step. Unless something else is done, the efflorescence will be back soon.

In order to prevent effloresce, you’ll need to:

  • Eliminate soluble salts for your concrete or masonry, and/or
  • Prevent water from transporting soluble mineral salts to the surface

Soluble Salts

Fact: Eliminating soluble salts from your concrete and masonry will prevent efflorescence. Although simple in theory, soluble salts are present in all cement-based substrates, and in the vast majority of masonry, both decorative and structural. Soluble salts can be found in Portland cement, concrete aggregate, sand, and even in the water used in mortar and grout.

Measures to minimize soluble salts should begin when the concrete or masonry is cast or formed. Stabilizers are now commonly used in bricks and paver castings to immobile salts. Using low alkali Portland cement can help reduce efflorescence. A well-graded aggregate, using a low water-to-concrete ratio, and preventing premature evaporation of water during curing are all good ways to reduce mineral salts. And finally, water sources used in construction should be clean, potable, and salt-free.

Managing salt content is important, but when dealing with an existing structure the salt content is already established, the opportunity to reduce salt is long gone. However, there is an opportunity to prevent that salt from contributing to efflorescence. RadonSeal Deep-Penetrating Concrete Sealer can immobilize soluble salts. RadonSeal penetrates deep inside the concrete, stucco, and other cementitious substrates, to react chemically and bind the salts in place – effectively removing them from the efflorescence equation.

Water

Moisture management should be a major focus of your efflorescence prevention efforts. Efflorescence is far less likely to appear on dry surfaces. Remember, without water to dissolve and transport salts, efflorescence cannot exist.

In some cases, water sources are easy to identify and eliminate. Adjusting sprinklers, gutters, downspouts, and flashing, will prevent unnecessary wetting. Ensure grading and drainage around your foundation and slab properly moves water away. In other cases, the source of moisture can be a mystery.

Managing water movement in and out of your concrete and masonry is generally recognized as the easiest and most cost-effective means to control efflorescence. However, choosing the wrong type of sealer can exacerbate the problem.

If your source of water is from the negative side of your structure, (for example groundwater seeping through a foundation wall, or up through a below a concrete slab), then topical sealers, like epoxy, waterproofing paint, or acrylic, are NOT the solution. Topical sealers will only trap moisture and efflorescence below them, and eventually delaminate, crack, and peel. Situations like this require a deep-penetrating sealer that will prevent water from migrating to the surface. The best choice, in this situation, would be a deep-penetrating concrete sealer.

Above-grade concrete and masonry surfaces need to be protected from rain, sprinklers, and other above-grade water sources. In these cases, water repellency is most important – if water cannot get into the concrete, then it cannot dissolve salts and bring them to the surface.

Summary

Efflorescence is a very common and controllable condition. Breaking the chain of conditions necessary for efflorescence can be done with proper understanding and the correct products.