Efflorescence (Lime/Grout Bloom) on Grouted Tile Joints

By the Ardex UK Technical Department

Efflorescence is a well-known construction phenomena that can affect the exposed surface of all products based on Portland Cement. It is a not a product performance issue, rather a chemical reaction deposit that can be mitigated or removed. An example of efflorescence from masonry mortar on brickwork is shown below.

The Tile Association describes Efflorescence as “a variety of chemical salts, i.e. carbonates, which can precipitate out into the surface of bricks, tiles, mortars and grouts”. It usually results in a lightening of the colour of a tile grout and, in severe cases, a white deposit on the surface.
For efflorescence to occur, the chemical reaction requires three elements; (1) a source of calcium salts, (2) exposure to air and (3) movement/accumulation of moisture. Factor (3) is the one that installers need to understand.

Where efflorescence forms on the surface of the ceramic tile joints, this effect is normally a result of slow drying conditions and is usually more evident on darker coloured grouts. It can occur on the grout surface where the surface of the grout mortar remains wet during the setting and hardening period, resulting in soluble lime in the mortar accumulating on the wet grout surface. The same effect can occur where water from the wet cementitious bedding beneath the tiles can rise to the surface of the joints and evaporate, leaving a deposit on the surface of the joints. Efflorescence is described in clause 11.3 of BS 5385-3:2014 Code of Practice for the design and installation of ceramic floor tiles and mosaics and “The Cleaning and Maintenance of Wall and Floor Tiles” and is a well-documented issue.

The following factors are important to minimise the risk of efflorescence (lime bloom) occurring on tile grouts;
• Mix water in the grout – do not overwater. Follow the grout manufacturers water dosage guidance.
• Washing off – do not over wash. Over washing can increase the amount of water in a grout, and can also increase the risk of standing water being left in the grout line.
• Moisture from the under the tiles – allow time to dry. Moisture from the substrates (concrete, screeds etc.) and the tile adhesive can come through the grout lines. The drying times of the substrate and adhesive are extended by larger format tiles, thicker adhesive beds, narrower joints, cooler temperatures and poor drying conditions.
• Site conditions – must facilitate drying: low temperatures, high humidity and poor ventilation will slow the rate of drying.

Efflorescence (lime bloom) is only an aesthetic deposit and does not affect the performance of a grout. It can be removed by a proprietary grout cleaner as shown below, but it may take repeated treatments to resolve. Do not use acids or masonry efflorescence removers on grouts as they may damage the grout and tile surface.

In hard water areas, the water itself can leave a white deposit. The photo below shows a 150mm x 150mm black glazed tile which has had water applied to the surface and left to evaporate overnight. This resulted in a white mark remaining due to the lime content in the water, with no grout having been used.

In external locations, where the tiling is exposed to weather, the conditions of exposure will have a marked effect on the potential for efflorescence and lime bloom. Efflorescence of this nature can continue for many years and is difficult to prevent or control, so it is always important to ensure that parapet detailing, flashings and similar are effective, adequate falls and drainage are provided, any movement joints are tightly sealed, as well as ensuring that the external tiling is solidly bedded with the joints solidly filled with grout mortar.

Contacts as below for expert advice on how to deal with efflorescence and the appropriate proprietary cleaning products to use.