Preventing Efflorescence: Understanding and Mitigating Its Effects

Efflorescence is the formation of white, powdery deposits on the surface of masonry, concrete, or stucco. It is caused by water solubilizing salts inside or behind the masonry and bringing them to the surface. As the water evaporates, it leaves the salts behind on the surface, creating those whitish deposits or streaks. Efflorescence is typically not harmful, but it can be unsightly. Preventing efflorescence is important, as these salt deposits and the vapour may cause long term damage to the concrete structure and the steel structure within. Today we look into the causes and mitigating effects of efflorescence and how to protect against it.

What is Efflorescence?

Efflorescence is a phenomenon where water containing dissolved salts migrates to the surface of masonry, evaporates, and leaves behind salt deposits. It usually occurs due to water penetration and can be identified by the presence of white or greyish deposits on the surface of brick masonry. 

The salts can come from a few different sources – from the masonry materials themselves, from mortar, or from salts in the environment. Sodium, potassium, and calcium salts are some common types that contribute to efflorescence.

These deposits form when water penetrates through the masonry via capillary action. When the water reaches the surface and evaporates, it leaves the dissolved salts behind. Over time, these build up into noticeable white stains and deposits. If the conditions causing the water penetration are not addressed, the efflorescence can reoccur and get worse over time.

Causes of Efflorescence

Efflorescence is caused by soluble salts in masonry materials that are carried to the surface of the material by water or moisture. When the water evaporates, it leaves behind a white, powdery deposit of the salt on the surface. The main causes and sources of these soluble salts include:

Soluble salts in masonry materials

Bricks, concrete blocks, stucco, and other masonry building materials contain naturally occurring soluble salts. During manufacturing, soluble salts can get trapped in the materials. When the masonry gets wet, these salts dissolve and are brought to the surface.

Salts from de-icing chemicals, fertilizers, and concrete ingredients

De-icing chemicals, commonly used during winter for melting ice on sidewalks and driveways, pose hidden dangers to concrete structures. Salts in some fertilizers and ingredients in concrete or stucco mixes can also contribute to efflorescence. Not only that, but salts from de-icing agents like calcium chloride and sodium chloride can penetrate concrete and masonry materials, causing corrosion and deterioration over time. As water moves through the material, it dissolves these salts and deposits them on the surface as it evaporates.

Types of Efflorescence

Efflorescence can be categorized into two main types: primary efflorescence and secondary efflorescence. 

Primary Efflorescence

Primary efflorescence occurs when water soluble salts are inherent in the masonry materials used in construction, such as bricks, concrete blocks, mortar, or cement. As the wall dries during or after construction, moisture evaporates, carrying these soluble salts to the surface, where they form whitish deposits. The most frequent reason for efflorescence is this.

Primary efflorescence is most likely to occur in the months immediately following construction when there is excess moisture present. It may diminish over time as the soluble salts make their way completely to the surface. This type of efflorescence is generally harmless and mainly an aesthetic concern.

Secondary Efflorescence

Secondary efflorescence occurs when external moisture penetrates the masonry after construction is complete. Sources of moisture can include rain, snow, irrigation sprinklers, poor drainage, leaky gutters, or rising damp from groundwater. As this water evaporates, it deposits soluble salts from the exterior on the masonry surface.

Secondary efflorescence can happen anytime after construction when excess moisture is present. It indicates a problem with water infiltration that needs to be addressed, as continual moisture intrusion can lead to structural issues. Preventing water damage is key to avoiding secondary efflorescence.

Using Efflorescence-Resistant Materials

One of the most effective ways to prevent efflorescence is to use building materials that are resistant to the issue in the first place. Here are some key materials to consider:

Low-Alkali Cement

Ordinary Portland cement contains alkali compounds that can leach out and cause efflorescence. Using low-alkali cement reduces the amount of alkali available to react. This type of cement has a maximum alkali content of 0.6% expressed as sodium oxide equivalent. Be sure to verify the alkali level before purchasing.

Latex Admixtures  

Adding latex polymer admixtures to cement mixes can make them more impervious to moisture penetration. The latex particles bind to the cement, filling in pores and creating a denser matrix. This prevents moisture and alkalis from migrating to the surface. Latex-modified mortar and concrete have become common options.

Coatings and Sealers

Applying specialty coatings and sealers to finished cement surfaces creates a protective barrier that prevents moisture infiltration. Silane, siloxane, silicone, and acrylic coatings are often used. Sealers need to be reapplied periodically as they wear over time. Proper surface preparation is also key to ensuring good adhesion and performance.

Choosing the right materials is one of the best ways to proactively prevent efflorescence from occurring in cement and masonry projects. The extra cost of upgraded materials is modest compared to the expense of trying to remove efflorescence after it happens. Being thoughtful about materials can help projects look their best for decades.

Proper Drainage and Moisture Management

Proper drainage and moisture management are critical for preventing efflorescence. Here are some key strategies:

Install Weep Holes, Flashing, and Dampproofing

Weep holes allow moisture that has entered the wall to drain out. Install weep holes at the bottom of exterior walls, spaced every 16-24 inches. Flashing over openings like windows prevents water entry. Apply dampproofing or waterproof membrane to the exterior side of foundation walls. 

Create Proper Slope and Drainage

Grade soil with a slope of at least 6 inches over the first 10 feet to direct water away from the foundation. Install gutters, downspouts, and splash blocks to prevent roof runoff from pooling near the foundation. Extend downspouts at least 5 feet from the home.

Use Vapor Barriers

Install vapour barriers on the warm side of insulation (towards the interior) to prevent moisture migration into walls and attics. Use vapour barrier paints or membranes. Seal seams and penetrations.

Cleaning and Removing Efflorescence

Efflorescence can often be removed through simple cleaning methods. Here are some of the most common and effective ways to clean and remove efflorescence:

Water Washing

One of the easiest methods is to wash the affected area with water. Using a garden hose or pressure washer, spray the area to rinse away the powdery deposits. This may need to be done several times to fully remove the efflorescence. Make sure to thoroughly rinse and dry the area afterwards.

Acidic Cleaners 

Specialized efflorescence removers and acidic cleaners are available that help dissolve and wash away the mineral deposits. Products containing acids like phosphoric, hydrochloric, sulfamic, or glycolic acids work well. Follow the product instructions closely.

After application, the area will need to be pressure washed or scrubbed with a stiff brush to remove the dissolved efflorescence. Wear proper protective equipment when using acidic cleaners. Rinse the area thoroughly afterwards.

Pressure Washing

For more stubborn deposits, pressure washing is an effective technique. Pressure washers generate high water pressure to blast away the efflorescence. Use the appropriate pressure setting to avoid damaging the masonry. Move the nozzle in close, overlapping circles.

Make sure any nearby plants, landscaping, and other surfaces are protected before pressure washing. Rinse the area thoroughly after completion and allow it to fully dry. Repeat as needed until the deposits are gone.

Long-Term Efflorescence Prevention

Preventing efflorescence from reoccurring is crucial for maintaining the aesthetic appeal and structural integrity of masonry surfaces over time. Implementing preventative measures requires an initial investment, but it pays off exponentially in the long run by avoiding costly repairs down the road.

• Using sealants and water-repellants on exterior walls. Applying silane or siloxane sealants creates a waterproof barrier that keeps moisture from penetrating into the masonry. Though sealants require reapplication every 5-10 years, the upfront cost is minor compared to letting efflorescence accumulate.
• Directing water away from foundations with proper landscaping. Installing drainage, downspouts, and sloped surfaces prevents pooling near structures. Well-designed landscaping is a permanent solution for diverting ground moisture. 
• Maintaining sealants and paints on concrete. Checking for cracks in coatings and reapplying as needed prevents water intrusion and efflorescence. An ounce of prevention saves a pound of repairs later.
• Cleaning efflorescence annually. Gentle removal using appropriate cleaners stops buildup before it becomes severe. Annual maintenance is more cost-effective than sporadic, heavy-duty cleaning.

With diligent prevention methods, efflorescence can be stopped in its tracks. The minimal regular investments pay dividends over time by keeping structures aesthetically pleasing and free of damage. Preventing efflorescence requires foresight and commitment, but the long-term benefits make it well worth the effort. Hiring a concrete contractor in Edmonton for preventative maintenance of your concrete surfaces is most viable and feasible in the long run.