Joints with a Soft or Powdery Surface

Visualisation

The surface of the grout joint disaggregates either at a simple touch or when scratched with a steel point, while exerting hardly pressure, and leaves stains on the fingers. In other cases, it displays disaggregated contaminations on the surface or efflorescences of whitish salts.

Defect assignment

Always under the assumption that we are using an industrial product supplied in closed bags, the appearance of powdery surfaces or with low scratch resistance will suggest there has been excessive evaporation of the water needed for hydration or also high suction of that water by the walls or bottom of the joint. In certain compositions and under particular weather conditions, migration may occur of resins or other components towards the surface, leading to the same result as a deficient hydration of the cement. This also happens with grouts past their use-by date.

The presence of efflorescences in permeable joints may also be a precursor to the break-up of the joint material, with a more or less powdery appearance.

Cement-based grouts have limited chemical resistance. When they are subjected to aggressive cleaning or disinfection operations, or are attacked by highly concentrated chemicals or especially aggressive products, the result will be corrosion of the joint surface with an ensuing loss of material, loss of abrasion and scratch resistance, and a more or less powdery state or rough texture.

Exceptionally, this defect may also develop when contaminations occur during the grouting operation, with the presence of foreign materials that make it difficult or impossible for the joint to mature.

Even reaction resin grouts (RG) have a limited chemical resistance, which depends on the attacking product and the grout exposure time. In the case of inappropriateness for use it will be necessary to examine whether the defect appears in a uniform way in the tiling or in a selective way as a function of the area. It should be borne in mind that RG materials have low resistance to the cleaning with pressurised hot water.

Efflorescences appear in joints filled with cement mortars that display high porosity and that, consequently, allow soluble salts to migrate from underlying layers of the ceramic tiling. When the water evaporates, the salts it contains will be deposited on the joint surface in the form of whitish stains, with a powdery feel. The appearance of efflorescences in the joints, independently of whether they appear on the ceramic tile or not, signals the presence of moisture and soluble salts in the ceramic tiling system.

It will depend on the type of grout involved whether more or less acid cleaning operations can be performed to remove the salts present (calcium, magnesium, or barium sulphates). The problem of these efflorescences will only cease, if salt migration through the joints stops.

Prevention

• Select grouts of type CG 2
• Select waterproof grouts [types CG 1W, CG 2 ]
• Select RG reactive resin grouts with chemical resistance in accordance with the expected chemical aggression in the tiling
• Use clean mixing receptacles and potable water
• Protect the tiling after the grouting, also against operations by other trades
• Verify that the grout is not past its use-by date