Jim Percival, technical director at Palace Chemicals, turns his attention to grouts, a topic which can be overlooked since it’s normally the tiles themselves that are the ‘main attraction’ in any tiling installation. However, the grouting stage is critical in a tiling project.
ALTHOUGH grouts have an important aesthetic function, they do a lot more than that. While most grouts don’t provide a fully waterproof barrier, they’ll 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.
An important first stage is to make sure the right type of grout has been specified. While a standard cementitious wall tile grout is suitable for many installations with a joint width of up to 3mm, on floors 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.
Specialist calcium aluminate cement grouts such as Colour-lock will ensure the finished colour shade is consistently achieved without being affected by efflorescence or shade variation. It’s also important to ensure the chosen grout is compatible with the tiles as some tiles don’t get on with coloured grouts. Some tiles have a very soft glaze, which could scratch when grouted, while porous or heavily texture tiles need to be pre-checked with a trial application to ensure absorption of grout into the tile face is not adversely affecting the desired finish.
Another potential problem 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 a more porous 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 the manufacturer’s recommendations, causing staining owing to the pH level of the cement. Excess water in the mix can also cause it. To achieve a good result, ensure 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. Best practice is to always grout a small inconspicuous area or a spare tile before grouting the whole area.
Problems can be caused by errors of preparation, application technique, or unsuitable curing conditions. Getting these stages wrong can affect the finished appearance and the structural integrity of the installation.
Undesirable variations in grout colour can be caused by adding too much or too little water during mixing or by using dirty water during clean-up. Grouts can also become stained if they’re exposed to moisture or dirt before they’re properly cured and sealed. It’s essential that a two-stage clean-up process is followed whereby the second wipe-off is done with a drier sponge or cloth to remove excess water in the joints before the grout has fully set.
Grout haze can also form. This is a cloudy film on the tile surface, comprising grout residue which has been allowed to dry on the surface of the tile. To avoid this, it’s important to clean away excess grout with a slightly damp sponge as soon as possible after application. Efflorescence is a potential problem with tiled surfaces which can ruin the initial aesthetic appearance of an otherwise good tiling job. No fault of the installer, this natural occurrence could happen at any time, however its effects can be mitigated by following a few careful steps, including sealing the substrate prior to tiling and ensuring the correct water level advised for the specific grout mix on the pack instructions is used, both when mixing the grout and then when controlling the surface clean-up and wash-off.
White salt deposits, indicating efflorescence, can appear on any tiled or other surface where the substrate is a recently laid cement screed or wall plaster which has not been primed or sealed prior to fixing the tiles.
In itself, efflorescence is not damaging to the grout, and the effect is a transient one as the grout is re-wet and then dries out. It’s usually encountered in new or recent constructions. Efflorescence can be minimised and controlled by ensuring the substrate is dry, sealed and the ambient temperature is preferably at least 10deg C. British Standard BS 5385-4 does not recommended tiling below 5deg C, ensuring the grout can harden, set and cure within the timescale expected in good, dry ambient conditions.
Since moisture is a key factor in the development of efflorescence, care should be taken not to include too much water in the mix of either the tile adhesive or the grout. Manufacturers’ recommendations should be adhered to ensure the mix is correct. The cleaning-off process should also be carried out without the use of excessive water, using a wet then dry wipe method of cleaning off grout residues without leaving excess water on the joints.
There are specialist cleaning products available on the market that will remove efflorescence from the grout face, but care should be taken when using these products as they’re usually made with acid that could burn and damage the grout.
Other issues that may occur are when the grout remains soft or fails to harden. This would normally be because too much water was added to the mix or if additional water was mixed in after the initial setting process had begun, or if a non-waterproof grout was used in a wet area like a shower.
Ensuring joints are clean and free of debris before application is crucial. Gaps can occur when the grout isn’t compacted properly into the joints using a grout float. This can trap air bubbles. Moving the float in the same direction as the grout lines can also pull material back out of the joints, even if they appear full. When they start to dry, the joints slump and will dip in the grout joint.
The key to avoiding most of these problems is to follow the manufacturer’s instructions and British Standards carefully regarding mixing ratios, application techniques and curing times. Applying a grout sealer after the curing period is a final important step to protect against moisture and stains, ensuring an attractive and durable tiled finish.
Palace Chemicals • www.palacechemicals.co.uk
