James Hailstone, ARDEX training and technical support manager for Scotland, explains some of the typical issues tilers might face with cementitious-based grouts and how to avoid them.
Cementitious-based grouts come in a wide variety of colours, making them ideal for most tiling situations. Essentially, cementitious-based grouts consist of a cement binder, fillers, polymers, pigments and other additives which when combined give the grout its colour.
Whilst the EN standard for grouts assesses the physical and mechanical characteristics and performance of the grout, the grout’s appearance and colour perception can be influenced by how the grout is mixed and applied to the tile joints, the colour and type of tile installed as well as on site conditions.
The way in which the grout is mixed and applied can have a direct influence on the degree of hydration of the cement binder and therefore influence the final grout colour shade. It is, therefore, equally important to ensure that the same amount of care and attention is taken when applying any grout as it is for the application of the tile adhesive.
The grout you select can also have an influence on colour consistency. While some other brands contain separate colour fillers in the mix, our grouts contain built-in colour fillers within the grout. This means you can mix up partial bags and still gain colour consistency, while other brands need the entire bag to be mixed for colour uniformity.
Fixers should also be wary of other common grout issues encountered on a regular basis, including colour variation between grout joints, efflorescence and cracking/debonding of grout joints.
Colour variation between grout joints can be caused by a number of issues. Firstly, variation in water content between mixes of grout. Ensure you are consistent in the amount of water used from mix to mix.
Other causes of colour variation include changes in temperature and atmospheric humidity during the grout drying phase, delayed cleaning up of the grout, overwashing during the initial clean-off process and also still wet adhesive.
Porosity of tiles may affect hydration i.e. by removing moisture from the grout. Try to use tiles with a similar absorbency on each visual plane. For example, ceramic tiles have more absorbency than porcelain tiles, meaning the grout will dry quicker in these areas and could affect colour consistency.
Lighting conditions on site can also cause colour variations. British Standards state that: “The type, direction and intensity of lighting at the time of tile fixing should not be appreciably different from the ultimate permanent lighting.”
Recessed grout, or minute differences in plane between tiles can also cause colour variation, and if the finished tiling is subsequently exposed to lighting from a different source, its appearance might be affected.
Another common issue with grouting is primary and secondary efflorescence – where excess salts rise through the grout causing white discoloration. Primary efflorescence can be caused through the use of an OPC cement in the mix, while secondary efflorescence is caused often as a result of damp rising through the sub-base or a high-water table, or other issues such as wet adhesive.
To protect against primary efflorescence, one could use non-OPC cement-based products. To ensure your grouting isn’t affected by secondary efflorescence, ensure that all direct-to-earth sub-floors have a suitable DPM before tiling.
Delay work in colder temperatures and increase site temperatures where possible. It is important not to work below 5°C and to protect any work from inclement weather when working outdoors.
Excessive water being used during the cleaning off process can also cause efflorescence, so ensure you are always using a damp, rather than wet, sponge. So can high humidity, so delay until conditions improve or dehumidify the room in very damp conditions.
Other causes of efflorescence include: mixing the grout too wet before application and grouting too early i.e. while the tile adhesive is still wet.
Perhaps one of the worst issues of grouting is cracking of the grout along the length of the tile edge. This can have numerous causes including: movement stresses, vertical deflection, drying shrinkage, thermal expansion and contraction and moisture expansion.
These issues are normally a result of poor installation and preparation – particularly the lack of adequate movement joints in the installation, deflection in the substrate, tiling onto uncured newly laid construction backgrounds and inadequate bonding of tiles into the adhesive bed (i.e not solid-bed fixing).
Grout can also crack across the grout joints – which is called ladder cracking. This is caused by shrinkage within the grout due to rapid moisture loss. To prevent ladder cracking, allow the grout to dry at temperatures not exceeding 25°C. You should also check porosity of the tiles, as this can cause ladder cracking. Other causes of ladder cracking include mixing the grout too wet before application and mixing the grout with the incorrect powder to water ratio.
Need support with your grouting? Call the ARDEX Group UK training and technical support team on 01440 714939 or visit our brand website HelpCentres.
helpCentre.ardex.co.uk
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