The experts at Quikrete provide tips and tricks on how to deal with concrete efflorescence.
It can be quite frustrating when this white, chalky substance known as efflorescence or “new bloom” shows up on your freshly poured surface. Fortunately, efflorescence can be treated and removed and prevented in the future.
The experts at Quikrete shared with us the causes, treatments and prevention methods for the build-up of efflorescence.
What is efflorescence and what causes it?
Efflorescence is defined as the appearance of an undesirable powdery substance on the surface of concrete or mortar. Typically, this white or cream discoloration of concrete and masonry forms when soluble salts and other water-dispersible materials surface through capillary voids in the mix due to temperature changes, wet migration, condensation, rain, dew, and / or too much water. It can happen quickly or over time, but either way, blooming can turn an otherwise attractive concrete or masonry surface into an unsightly eye pain on a building, house, or other structure.
Any material that contains Portland cement is prone to efflorescence. It generally occurs when calcium hydroxide (lime), formed in the cement hydration reaction, is carried to the surface by water through capillaries in the concrete. There it combines with carbon dioxide from the air to form calcium carbonate and water. However, efflorescence can also be caused by hydroxides and sulfates of sodium or potassium, which are much more soluble in water than calcium. And they bloom faster than calcium hydroxide.
These salts can come from cement, aggregates, water or additives. In both cases, the result is a white discoloration that contrasts with the color of the concrete or masonry surface.
How can efflorescence be avoided / prevented?
It may be difficult to avoid blooming completely, but there are effective ways to prevent or minimize blooming by controlling the three factors:
- Soluble salts
- Migrate channels
Concrete and mortar manufacturers can use high quality and clean ingredients, add pozzolans and other lime-consuming materials, incorporate water-repellent and other blooming additives.
Contractors should use the correct amount of mixed water and the correct curing techniques to reduce the matrix porosity and water absorption of concrete. Quikrete Acrylic Cure and Seal is an anti-efflorescence agent because not only can it cure concrete and mortar more effectively, but it also forms a topical sealant coating to prevent outside moisture from penetrating concrete.
How can efflorescence be removed?
Despite all efforts to prevent blooming, it can still occur. While sandblasting is a traditional option for removing efflorescence, this process can etch damage and weaken the concrete masonry surface. Specially formulated water-based chemical treatments like QUIKRETE Efflorescence and Rust Remover offer a simple, safe, and effective alternative to sandblasting.
QUIKRETE Efflorescence and Rust Remover, a solvent-free, low VOC product, can improve concrete and masonry surfaces by removing efflorescence in just four steps.
Note: Always wear rubber gloves, eye protection and rubber boots when working with detergents for concrete and masonry.
- Sweep and remove all dirt and debris from the surface
- Dilute the product to a 1: 4 dilution in a plastic container. Gently brush or spray diluted material onto surfaces. If necessary, a more concentrated dilution is appropriate. However, be careful to avoid etching the surface
- Let the material work for a minute
- If there is a lot of efflorescence, scrubbing with a medium to stiff nylon brush will improve removal. Rinse thoroughly with water
QUIKRETE Efflorescence & Rust Remover should be tested on an inconspicuous area before treating the entire area in order to optimize the application technique and evaluate the effect.
If my project is blooming, is it a structural problem or a cosmetic problem?
Most of the efflorescence on concrete and mortar is cosmetic only.
Proper cleaning and prevention can usually produce satisfactory results for owners.
In some very rare cases, excessive efflorescence is associated with flaking, deterioration, and structural failure. This can indicate other durability issues, and it can take engineers some time to figure these out and fix them.
Will it go away in time?
Usually the efflorescence does not go away completely over time. However, slight efflorescence may fade or mix with the surrounding area due to aging or weathering, and there may not be a need to treat or clean it.
Published courtesy of Quikrete.