Jim Percival, technical director at Palace Chemicals, looks at some of the technical considerations involved in the successful selection and use of grouts
The grouting stage is critical in any tiling job. We tend to think of grouts as serving primarily an aesthetic function – and that is of course important – but they do a lot more than that. Although not waterproof, in most cases, they will nonetheless help to inhibit the passage of moisture into the substrate behind the tiles. By filling the gaps between tiles, the grout line also adds structural rigidity to the whole installation, preventing the tiles from moving over time.
With regard to the aesthetic aspects, there is a wide variety of options. These basically fall into one of two camps – complementing or contrasting. An example of a complementing grout colour would be the use of white grout with a white tiled installation, and this is probably still the most common solution. However by going for a contrasting approach and choosing a grout colour that really stands out, or picks out a colour from the pattern on the tile, a striking effect can be achieved.
There are a number of considerations that should be borne in mind when choosing and installing a grout.
Firstly, make sure that the right type of grout is being specified. Whereas a standard cementitious grout is suitable for many installations with a joint width of up to 3mm, where joints are wider – up to 20mm – a polymer-modified, flexible wide joint grout should be used. For jobs where hygiene is important or where moisture levels are high, an anti-bacterial or epoxy based grout will be desirable. These will inhibit the formation of black spot mould and discolouration. Colour-lock versions will ensure the finished colour shade is consistently achieved without being affected by efflorescence or shade variation.
When using grouts, there can be a risk of staining the tiles. Some tiles have surface porosity or micro-porosity, meaning that the grout colour can be aborbed by the tiles, resulting in staining.
This risk is higher when a pigmented grout is applied. For this reason, it is essential to test the potential risk of staining on a few unused tiles before grouting commences. If discolouration occurs then the tiles should be sealed with a proprietary tile sealer and then the test should be repeated. A number of coats of sealer may be required depending upon the degree of porosity of the tile. It is recommended that advice is sought from the manufacturer of the sealer.
The most commonly affected tiles are certain ceramic and natural stone types. However, this can also occur on some porcelain tiles as the high firing temperature can create micropores in the tile surface.
Another issue is “picture framing” or “tram lining”. This is when a cement film has dried around the surface edge of a tile and is caused by water or fines in the grout being drawn by capillary action into the tile body through the grout joints. This can occur with very porous tiles or tiles with a translucent glaze finish. In these instances an impervious grout should be used instead of a cement-based grout.
Picture framing can also be caused if excess grout is left on the tile for longer than manufacturer’s recommendations, causing a mark due to the pH level of the cement. Excess water in the mix can also cause it. To achieve a good result, ensure that the grout manufacturer’s recommendations are followed regarding the powder:water ratio and also mix the grout thoroughly to ensure a smooth lump-free mix of uniform colour.
Ensure that a damp sponge is used to wash off, do not over-water as this can result in a streaky finish as well as causing efflorescence – the trail of white salt deposits which can appear on a tiled surface or any other surface where cement is involved, either in the covering material or in the substrate. Efflorescence is usually encountered in new or recent constructions and is more likely to appear at certain times of the year in the UK, especially during colder temperatures.
www.palacechemicals.co.uk