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Surface coatings

Coatings may be used as part of the repair process to provide additional protection to both the existing concrete and the repair. They have a limited life and must be maintained if they are to remain effective. They can slow down the corrosion process by reducing carbonation and ingress of chlorides and moisture, and cutting off the supply of oxygen to cathodic areas. There are many different types of coating generally grouped into three main categories.

Barrier coatings form a physical film on the concrete surface typically 300 microns to 1 mm thick.
Pore blockers penetrate the minute capillary pores to a certain degree, solidifying to produce a plug of polymer or crystal growth in each pore.
Pore liners penetrate the concrete surface without forming a surface film and react with the silica present in the paste to produce water-repelling compound.

A fourth group of products are Sealers. They penetrate and also form a thin film on the surface. Materials of this type are sometimes used to bind together and strengthen weak surface layers.

Before any coating is applied, the concrete surface must be clean, free of any loose material. The manufacturer’s requirements for temperature and moisture condition of the surface and for ambient temperature and relative humidity during application should be established and observed. Depending on the type of material, coatings can be applied by brush, roller or airless spray.

Acknowledgement: The Concrete Society

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TR50 Guide to surface treatments for protection and enhancement of concrete