How do I remove efflorescence?

Efflorescence is a natural phenomenon that occurs in any material that contains cement (lime) and comes in contact with water. The process involves natural salts which migrate out of the concrete (or mortar, block or brick), triggered by exposure to water, which react with Carbon Dioxide (CO2) in the air to form Calcium Carbonate (CaCO3) on the surface. These salts will take the path of least resistance up through the concrete to reach the surface. The concrete’s surface profile, color, water-cement ratio and porosity all play a part in the formation of efflorescence.

When the cause of the efflorescence is excessive water forcing the migration of (salts) up through the concrete, than the 1st step is to eliminate the source of the water.

Once the water source is eliminated, most efflorescence (also called Calcium Carbonate or limestone) can be removed with abrasive techniques. Dry brushing, light water blasting or light sandblasting followed by flushing with clean water. In large areas, rotary scrubbers with scrubbing pads may also be used. It is best to use the least amount of water possible for removal or rinsing of the efflorescence. The more water applied, the greater the risk of starting the efflorescence reaction all over again. NOTE: If a curing and sealing compound has been previously applied, it will be necessary to remove this product thoroughly, prior to removal of the efflorescence.

If the efflorescence appears to be insoluble in water, it may also be necessary to wash the surface with a commercially available weak acid solution cleaner or specialty efflorescence remover. NOTE: For integrally colored concrete, use only a 1-2% acid solution to prevent surface etching which may change the color and the texture of the concrete.

Precautions:

-Follow ALL safety, handling and application instructions of the cleaner prior to use.

-Before any acid treatment or efflorescence removal, a small, inconspicuous area should be treated prior to treatment of the entire slab, to ensure there are no adverse effects.

-Acid treatments may change the appearance of the concrete; the entire surface (as opposed to “spot” applications) should be treated to avoid discolored or mottled areas.

-Before applying any acid solution, always dampen the concrete surface with clean water to prevent the acid from being absorbed deeply into the surface.

-After treatment with any type of acid solution the concrete will need to be neutralized thoroughly. A solution of baking soda (sodium bicarbonate) and water (Approx. 1 lb. Of baking soda per 5-gallons of water) can be used to neutralize the stain. The solution should be applied until it stops fizzing. After neutralization is complete, the surface should be rinsed thoroughly with clean water several times to remove all remaining residue. NOTE: Runoff may stain adjacent areas or harm plants. Runoff should be collected by wet vacuuming or absorbed with an inert material. All stain residue, runoff liquid, rinse water, and absorbent materials used during application must be collected and disposed of in accordance with local, state, and federal regulations.

After rinsing is complete, a pH test should be performed on the surface to verify that no residual acid is present. If the color indicates a pH of 7 or higher, no residual acid is present and surface is ready for sealer application. If color indicates a pH lower than 7, further neutralization is required.

FAILURE TO COMPLETELY REMOVE ALL ACID RESIDUE PRIOR TO SEALING THE SURFACE WILL CAUSE APPEARANCE DEFECTS, ADHESION LOSS, PEELING, REDUCED DURABILITY, DELAMINATION AND POSSIBLE BOND FAILURE OF THE SEALER.

-Allow the surface to dry thoroughly if it is to receive a subsequent coating or adhesive.

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