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THE LAYING PROCEDURE OF IMPRINTED CONCRETE.

E F F L O R E S C E N C E

WHAT IS EFFLORESCENCE?

Efflorescence is a deposit usually white in colour that may appear on the surface of imprinted and coloured concrete. One of the preliminary reasons it occurs is due to water evaporating from the surface of the concrete leaving behind a white or grey deposit of soluble salt. Efflorescence appears just after a structure is completed and is generally harmless but these deposits can occur within the surface pores of the material causing expansion that may disrupt the surface.

The two types of efflorescence are PRIMARY and SECONDARY.

In PRIMARY Efflorescence the water used in the production of the concrete migrates to the surface and evaporates leaving behind soluble salt deposits.

SECONDARY Efflorescence is due to the ingress of water from an external source. this water picks up soluble salts present in the concrete and migrates to the surface, evaporating and depositing the salts on the surface of the concrete.

Efflorescense is mostly affected by temperature, humidity and wind. It is most obvious in winter, this is so as the rate of evaporation is slower in winter, therefore allowing salts to migrate to the surface. However Efflorescence may be observed throughout the year following heavy rains and drops in temperature. Its appearance can be light-coloured and blotchy to a white coating but as the years pass it becomes less extensive unless there is an external source of salt.

PREVENTING EFFLORESCENCE

The reduction or overall elimination of Efflorescence can be accomplished by certain methods.

To reduce or eliminate Efflorescence the following are applicable:

Never use unwashed sand.

Use low Alkali cement.

Use clean mixing water free from harmful amounts of acids, akalis, organic material, minerals and salt.

Apart from these easy to follow steps there are other methods to combat Efflorescence. These methods concentrate mainly on consistency and composition of cement.

Water soluble admixtures offer only short-lived protection. Calcium Stearate Dispersion (CSD) is the most common Efflorescence Control Agent (ECA). It is a water soluble wax based compound. Its water repellant and ECA properties offer only temporary protection.

REMOVING EFFLORESCENCE

Low absorption of moisture is the best assurance against Efflorescence. To achieve maximum watertightness, concrete must be made with properly graded aggregates an adequate cement content, a low water cement ratio and thorough curing.

When Efflorescence occurs the source of the moisture should be determined and corrective measures taken to keep water out of the structure.

Most Efflorescence can be removed by the following:

Dry-brushing

Water rinising with brushing light

Light water blasting

Sand blasting followed by flushing with clean water.

On a mild case an application of straight vinegar followed by a thorough rinsing with water can remove the deposits. The last resource if none of the mentioned remove the deposits is to apply a dilute solution of imuriatic acid ( 1 to 2%).

PROCEDURE

1. Before applying an acid solution dampen the surface with clean water to prevent acid from being absorbed deeply into the structure where damage may occur.

2. The application area should be no longer than 4sq ft with a delay of about five minutes before scouring off the salt deposit with a stiff bristle brush.

3. After this treatment the surface should be immediately and thoroughly flushed with clear water to remove all traces of acid.

Caution: Rubber gloves, glasses and other protective clothing should be worn by crew members using an acid solution.

CONCLUSION

To conclude it is best to try all other possible means before using acid solution due to the possible adverse on Coloured Concrete.