Case 1

Remedial (see also Remedial)

The use of algicides, toxic washing and repainting of walls every few years is useful in preventing such growth to stay permanently on the façade. High water pressure jet may be used [2-3].

Algae, mosses, fungi that grow on the external façade of the building can be readily killed by a number of chemicals. Some of these chemicals leave a toxic residue to deter further colonization. One of the following method can be used:

1. Apply a solution of domestic bleach and after a few days, scrub or scrape off the dead material which should come out from the surface easily;
2. Spray fungicide or algicides on the growth in accordance to manufacturer’s instructions and coat with water repellant and paint;
3. Treat it with 5% solution of magnesium silicofluoride crystals in water.

Apply coatings over surface to prevent water from retaining on the external wall.

Find the source of water ingress if any, stop further water ingress using methods such as sealing, injection, impregnation (see Remedial).

The affected areas should be washed cleaned with pressure jet and an abrasive cleaning agent. Washing should begin from the top. After the dust and dirt have been removed, the debonded tiles can be re-patched. Care must be taken in selecting the adhesive used so as to ensure effective adhesion to the concrete backing.

Removal of Efflorescence

-If efflorescence exists on an existing surface, the best method of cleaning or removing it, would be to use an acidic cleaner. These salts and minerals would readily dissolved in these acidic cleaning agents.
-Care should be taken when using these acidic agents which may be corrosive in nature.
-Occasionally, the cleaning and removal process can become more difficult if latex or chemical transmission occurs at the same time as the salts and minerals surfaced. These latex or comparable chemicals are often found in the more recent and advanced cementitious adhesives and grouts available and can form a protective layer which defends the efflorescence from direct contact with acidic cleaning products.
-To help solve this problem, select an acidic product that has cleaning agents in it (acid and cleaner in one single product). Another recommendation would be to use a high alkaline restoration cleaner to break down the latex protective coating, rinse well and then proceed with the acidic cleaning.

Repair: Application of Water Repeller

This type of solution act as a hydrophobic surface by penetrating into the pores of the bedding or screed layers and tightening the pores such that the water is not allowed to penetrate through.

It allows vapour to escape and prevent any development of hydraulic pressure caused by the retained moisture.

Repair: Application of Water Proofer (Silicate based)

This kind of solution reacts with the free lime in cementitious materials and seals the pores and cracks in the surface. In fact, as long as moisture and free alkali is present, the reaction will continue by sealing pores. This can also be referred to as “active” repair.

Repair: Application Water-based Clear Coating (with polymer particles)

In this treatment the floor is ponded with the solution and allow the super fine polymer particles to penetrate into the porous structure to form a permanent and continuous plug.

Regular mechanical or water-jet cleaning of stonework to remove growths is both costly and can, in itself, cause deterioration of the stone surface. A more appropriate method of treatment is the application of SURFACE BIOCIDES which kill the existing growths and have residual action to inhibit re-colonisation.

In general, these are applied as part of an overall cleaning strategy which comprises:

1. An initial spray application of a biocide in a water-based formulation which usually results in existing growths dying off and becoming at least partially detached from the underlying stone.
2. A mechanical cleaning procedure 3-4 weeks later using a dry brushing process with a soft hand brush to remove the loosened growths.
3. Finally, re-treatment with a biocidal formulation to prevent re-colonisation of the cleaned stone.

However, note that treatment will only last for a limited number of years and after which the chemical will wear out, and re-colonisation will occur again. The average is known to be approximately 2 years. The protection period is dependent on the degree of site exposure and the environmental condition it is in.