Response to Mr. Thompson’s letter
Mr. Thompson has raised some interesting points concerning grouts and BAL is happy to offer some general comments in response.
First, a brief word about grout chemistry. When Portland cement, the basic binder within most cement based grouts, is mixed with water it reacts to form complex crystalline hydrates, as well as hundreds of additional minor products which are more complex and unpredictable. The grouts also contain cement, pigments, differing fillers, polymer additives and other minor additives which combine to give the product its resulting colour.
Manufacturers such as Building Adhesives Limited can do their part in producing quality grouts by using the best raw materials available. Building Adhesives Ltd ensures that these are tested both by the raw material producer and tested internally before use. Then Building Adhesives Ltd test each batch of manufactured grout is tested for Quality Assurance and consistency, including colour, before it leaves the factory. A manufacturer can make good or bad batches of grout but, in the case of bad batches, these will be picked up by Building Adhesives Ltd at the QA testing stages and fail. Through this process grouts can not be produced which vary in colour shades from the same bag, or from bags within the same batch. In other words, if manufacturers follow stringent testing standards and use only the highest quality raw materials it is almost impossible to manufacture patchy grout.
A patchy effect can be created by the result of something other than the product itself. The most important thing to consider when working with any form of cementitious-based grout (pigmented or unpigmented), is to be as consistent as possible throughout the product use, particularly at the key statges of mixing, applying and cleaning-off these products.
In terms of mixing, by using different powder to water mix ratios in differing applications and areas the same bag of grout will obviously dry at slightly different colour shades.
In terms of application, even variations in the depth of grout can influence its colour. A fixer should make sure that any excess adhesive is scraped out of the joints before drying. Any excessive high spots, creating shallower grout joints, can result in a lighter colour.
Applying to differing tile types can also cause problems. Coloured grout placed between porous tiles, such as limestone or porous-bodied tiles with varying levels of excess glaze over the tile edges, can look darker because moisture can be drawn from the grout. If grout from the same bag were used between impervious porcelain tiles, it would appear lighter in colour. Polymer-modified grouts though will generally help to overcome this problem
Using a polymer admixture can also darken the grout colour. Again, consistency is the watchword. A fixer using a polymer admixture with a cement-based grout should ensure that they keep the mix ratio the same for every batch.
Overwashing during the grout cleaning-off process, or effecting a much drier clean-up, can result in the grout becoming either lighter or darker respectively. In the case of overwashing, any pooling or ponding of water on the tile and freshly applied grout will greatly increase the risk of efflorescence occurring. The likelihood of efflorescence is also influenced by temperature. When grouting in autumn or winter, the site temperatures should be, ideally, above 12° C. Below this figure, down to a minimum of 5° C, the drying process slows and the risk of efflorescence rises greatly.
In conclusion, whether a grout becomes patchy or not is, unfortunately, largely beyond the control of the grout manufacturer. Ultimately, it depends upon, for example, the speed and degree of hydration the cement undergoes in situ. As with efflorescence, this is very much driven by good working practices on site and, just as importantly, the environmental conditions and any wide variations in temperature and humidity during the grout’s drying out period. However, grouts such as those within the BAL Microcolour range are specifically formulated to significantly reduce the risk of efflorescence.
With so many considerations involved, correct working practices are vital for professional fixers and BAL supports these practices wholeheartedly. We ensure that the correct and consistent mixing application of our grouting products is a key part of our Fixer Training programmes, as well as advising fixers wherever possible on best practices through our packaging, literature, telephone, video and web communications. Fixers with questions on any aspect of grouting or tiling are encouraged to call our free Technical Assistance hotline, on 0845 600 1222, during normal working hours.
We appreciate Mr. Thomson’s comments as an experienced fixer and hope that we have given some clarification.
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For further advice and precise information, visit the BAL website at
or call 0845 600 1222