Stains and Discolorations

Visualisation

Numerous defects are included in this group, which affect the appearance of the joint pattern, materialising in a lack of colour uniformity, perceived at a medium distance. However, at a short distance the following may be observed:

• Remains of grout on the tile edges
• Areas of contrasting colour stains
• Point discolorations, in some cases accompanied by corrosion
• Blackened joints in certain parts of a wall tiling or floor tiling

Defect assignment

Standard EN 13888 envisages the water absorption of grouts once they have matured, which is in addition one of the classification parameters in CG 1 and CG 2. Although water absorption is associated with the impermeability of the grout, it may be extrapolated to surface porosity, which allows dirt to lodge and makes later cleaning difficult. The parameter of water absorption and surface texture will provide an indication of a greater or lesser difficulty in cleaning the tile-to-tile joints. In order to achieve characteristics and performance approaching those of ceramic tiles, a test method should perhaps be considered in the future that would allow evaluation of tile-to-tile joint cleanability.

On the basis of water absorption, the joints that are easiest to clean will be those filled with reactive resin grouts, because they should have a water absorption below 0.1 g and are the only ones that can really be classified as waterproof. Owing to their chemical resistance they also withstand more aggressive cleaning products without deterioration.

In addition to stains it is also necessary to consider a very important parameter related to health, and to humid or permanently wet environments. That parameter is related to the facility of mould growth and the settling of live matter at the joint surface, and it features, for instance, in the British standard test method for the measurement of resistance to mould growth. Owing to their alkalinity, cementitious materials are more resistant than those based on reaction resins. However, once the cultures have formed, the cementitious materials will undergo deterioration by chemical attack more quickly in vigorous cleaning operations.

Prevention

It has already been remarked that tile-to-tile joints should have identical resistance to the impairment of appearance as the ceramic tiles. However, grout characteristics differ from those of a ceramic tile, particularly if the tile is glazed. Based on the type of grout (CG cementitious or RG reaction resin grout), we should:

• Select waterproof grouts in wet applications or where there is a greater risk of stains; i.e. CG 1W, CG 2 or RG materials according to EN 13888
• Select RG materials, even with specific chemical resistance, where there is risk of chemical attack

In addition, in areas with a permanent presence of water, the resistance of the materials to mould growth should be envisaged (characteristic not included in EN 13888).

A quality tile installation demands the preparation of the materials in clean receptacles, the use of potable water and clean tools; however, it also requires careful final cleaning, with appropriate tools and, if it needed, protection of the tiling against operations performed by other trades (plasterers, fitters, painters…). It is highly advisable to use a different sponge for each colour.