Efflorescence on Grout
The grout is effloresced [Photo 1]. A white, powdery substance has accumulated on the grout of the tile joints and tiles.
Technical reasons for efflorescence on grout
Morgan advises that there may be multiple causes for the appearance of efflorescence.
In very light cases of efflorescence the installer has likely used too much water when mixing the grout and during the cleaning process. This has resulted in the puddling of water onto grout that has shrunk back due to a lack of body. The puddled water then draws & concentrates calcium salts at the surface as the water evaporates.
In extreme cases, water soluble minerals have been transported up through the grout with water. As the water evaporates at the surface, salts and other contaminants are deposited onto the installation. Usually this represents a situation where water from any nearby taps or other sources of water are moving upwards from under the installation and evaporating through the grout joints.
Recommended procedure for removing efflorescence on grout
It is important to determine the cause of the efflorescence first.
Grouts that have been mixed with too much water will usually shrink back into the grout joint and support a white efflorescence layer at the surface. Grouts that have been mixed with too much water therefore need to be removed completely and the entire tile installation needs to be re-grouted.
Grouts installations that suffer due to an external water source can usually be remediated by locating and isolating the installation from the water source. Sometimes waterproof membranes, falls & drains may have to be correctly placed and installed. In some cases, time will result in less and less salt being deposited at the surface of the installation.
Speciality organic acids can be used to soften & remove most calcium salt-based deposits. DO NOT use inorganic acids such as hydrochloric acid to treat efflorescence. Minor cases of efflorescence can also be treated with speciality oil products to bring out the grouts original colour without removing the efflorescence.