Efflorescence on tile grouts

Efflorescence is a white deposit, which develops on the surface of grout and/or tiles as drying out proceeds. It occurs as a result of soluble salts contained in Portland cement or materials used in conjunction with it.

These salts can come from the background, render, screed, as well as from the tile adhesive or grout. It is aggravated by excessive damp and humid conditions, which may occur after completion of an installation or where there is a prolonged delay in drying out. The white crystalline deposit often disappears after washing with clean water, but may reappear after drying. Persistent efflorescence can also arise from inadequate damp-proofing in the wall or floor structure. The white deposit formed is usually calcium carbonate, which is harmless, but detrimental to the appearance.

Efflorescence can be caused by: 

  • Soluble salts being present in the jointing material, adhesive-bed, or substrate on which the tiles were fixed.
  • Moisture must be contained in the setting bed, or joint material to dissolve the salts, allowing them to migrate to the surface

Evaporation or hydrostatic pressure must occur for the salts to migrate to the surface. With time, efflorescence diminishes, unless there is an external source of salts and water. Salts may be contained within the setting bed or grouting material, but salts can also migrate from the render, screed, or concrete background on which the tiles were fixed. Efflorescence is more noticeable on dark coloured grouts.

Occasionally, efflorescence can occur as a result of the methods used in finishing grouted joints between tiles, i.e. use of excessive water and methods adopted in wiping off surplus grout from the tiles, resulting in fine particles being brought to the surface along with the soluble salts. Efflorescence can be avoided by eliminating soluble salts from the bedding and jointing materials. In cement/sand bedding mortars or grouts, the use of sea or channel sand should be avoided and only washed sand should be used. In general, use of proprietary adhesives and grouts eliminates many of the sources of these salts. The presence of moisture from beneath the tile should be prevented and due attention should be paid to damp proof courses. In the mixing of setting materials, only clean water should be used and excess should be avoided. The use of accelerators in the setting material should also be avoided, as should the use of lime in any cement/sand mortar. In areas of high humidity, grouting should be avoided when temperatures fall.

In order to avoid efflorescence occurring, it is essential to eliminate the presence of water or damp which may be prevalent in the installation. It can sometimes be removed simply by washing the tile surface with water and perhaps cleaning the joints with a stiff bristle brush. Occasionally the deposit will disappear with time through normal service conditions. However, more often than not it is necessary for chemicals to be used in order to dissolve the white crystalline deposit from the tile or grout surface. For this, it is necessary to use acid based materials, and only “safe” proprietary products** should be used, in accordance with the manufacturer’s instructions. It is necessary to leave it in contact with the surface for a few minutes before thoroughly washing off with clean water.

When tackling large areas, it is important that correct techniques are employed before treatment of the whole floor, and therefore a small test area should be treated first. It is recommended that the installation should be allowed to thoroughly dry out, before any treatment with acid cleaners is carried out, as efflorescence could reoccur, if more soluble salts are brought to the surface.

In general, sealing of floor tiles is not recommended. However, if used, e.g. terracotta tiles, then the installation should be allowed to dry out completely and the grout have dried to the required colour, otherwise, once sealed, there will be no means of removal of the salt deposit.

** Products such as HG Limex or Lithofin Cement away are suitable, but should not be used on marble or limestone floors, as they will attack the tiles.

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