The Basics of Efflorescence
The term efflorescence refers to the unsightly, chalky, deposit that can be found on the surface of concrete, brickwork, pavers, or other masonry. It develops as naturally occurring mineral salts are transported from inside the substrate to the outside by moisture. It’s not uncommon for efflorescence to “grow” or “bloom”, forming fluffy hair-like fibers. In fact, the word “efflorescence” actually means “to flower out”, in French. Efflorescence is typically white, but can also be yellow or brown, depending on the type(s) of salt present. Efflorescence on your concrete, bricks, or pavers is mostly a cosmetic problem, but can also be a sign of a moisture issue that could lead to much bigger problems.
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 concentration of soluble salts, and therefore produce efflorescence most often. Clay brick, pavers, and low cement CMU’s present a lower risk, as the soluble salt content is lower. Although efflorescence stains on red brick can be quite common, the source of the salt is usually the cementitious mortar in between the bricks. Salt-laden water moves from the mortar into the porous brick and evaporates through the brick face, leaving efflorescence on its surface.
Efflorescence pushing paint off a garage wall.
Efflorescence bloom on basement concrete floor.
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Removing Efflorescence On Concrete, Brick, & Pavers
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 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 product details 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. It is generally caused by water originating from an external source leaching salts to the surface.
Secondary efflorescence is very common where hydrostatic pressure is high. When basements, storm cellars, or retaining walls show efflorescence, it is likely due to hydrostatic pressure. For example, as groundwater gathers around your foundation, it exerts pressure against your foundation walls and concrete slab. As pressure increases, the water eventually migrates inward through the capillaries and pores, making its way inside your home. As the water moves, it dissolves and carries salts from the soil, as well as salt dissolved from your concrete, with it. When the water dries, the salts are left behind.
Wind-driven rain, sprinklers, and frequent wetting and drying cycles are often the cause of efflorescence on above-grade walls and slabs. Cold and damp areas, like garages floors and shady patios and walkways, are more prone to this issue. Water evaporates more slowly in these areas allowing more salts to reach the surface.
While secondary efflorescence can be as aesthetically displeasing as primary, it is often considered a symptom of a larger moisture problem, requiring corrective measures.
When It’s 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 stain is no longer visible, when 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 in Concrete, Brick, & Pavers
Cleaning the visible stain is only the first step. Unless something else is done, the efflorescence will be back soon.
In order to prevent it, you’ll need to:
- Eliminate soluble salts for your concrete or masonry, and/or
- Prevent water from transporting soluble mineral salts to the surface
Managing Soluble Salts
Fact: Eliminating soluble salts from your concrete and masonry will prevent efflorescence. Simple enough, right? While simple in theory, soluble salts are present in all cement-based substrates, and in most other masonry materials, 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 and the opportunity to reduce salt is long gone. However, there is still an opportunity to prevent that salt from contributing to the problem. RadonSeal Deep-Penetrating Concrete Sealer can immobilize soluble salts and prevent concrete efflorescence from developing. RadonSeal penetrates deep inside the concrete, stucco, and other cementitious substrates, to react chemically and bind the salts in place forever – effectively removing them from the equation.
Managing Water
Water and moisture management should be the major focus of your prevention efforts. Efflorescence is far less likely to appear on dry surfaces. Remember, without water to dissolve and transport salts, efflorescence cannot exist. If possible, eliminating water exposure should be your objective. If this is not possible, focus on preventing water from getting inside, concrete, brick, or pavers. This process starts with identifying the source(s).
In some cases, water sources are easy to identify and eliminate. For example, adjusting sprinkler heads, gutters & downspouts, and flashing, can go a long way towards preventing unnecessary wetting. Ensure grading and drainage around your foundation and slab properly moves water away. Unfortunately, the source of moisture can sometimes be a mystery, or too costly and labor intensive to eliminate.
If the source of the water cannot be identified and/or eliminated, then the focus of your efforts should be keeping the water out of your concrete, brick, and masonry. Managing water movement in and out of your concrete and masonry is generally the easiest and most cost-effective means to control efflorescence. This can be accomplished by sealing your concrete, bricks, and masonry to prevent water from being absorbed. Be careful! Choosing the wrong type of sealer can exacerbate the problem.
How to Choose the Best Sealer
Choosing the right sealer to prevent efflorescence depends greatly on knowing where the water is coming from. As mentioned earlier, the wrong type of sealer can make the efflorescence problem worse. For example, when moisture orientates from below the concrete slab, or outside your foundation wall, a topical sealer or coating (acrylic, epoxy, & urethane) would be a poor choice. As hydrostatic pressure pushes salt-laden water through the concrete, efflorescence gets trapped below or behind the surface sealer and appears as a whitish blush or haze. In severe cases, efflorescence blooms can damage and delaminate coatings, flooring, or tiles, or cause paints to bubble, crack, and peel.
If the source of water is from the negative side of your structure, then the best choice would be a deep-penetrating concrete sealer that is resistant to hydrostatic pressure. Look no further than RadonSeal Deep-Penetrating Concrete Sealer for water-proofing your below-grade poured concrete and concrete block. Nothing seals deep or tighter. RadonSeal is permanent and leaves surfaces ready for paint, adhesives, or tiles. This is the great way to protect your flooring from damage cause by moisture and efflorescence. If you are dealing with a brick or non-cementitious foundation or retaining wall, use Ion-Bond Armor Surface Elastomeric Sealer. Ion-Bond is the only other sealer that can tolerate hydrostatic pressure and is approved for below-grade waterproofing.
Above-grade concrete and masonry surfaces, like building facades, chimneys, & hardscaping, are not subjected to negative-side hydrostatic pressure. These surfaces need to be protected from positive-side water (rain, sprinklers water, etc.). In these cases, water repellency is critically important. In these situations, use LastiSeal Brick & Concrete Sealer for an unbeatable 15-years of protection, or go for DryWay Water-Repellent Sealer, which is a DOT approved silane/siloxane water-repellent.
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.