Masonry Magazine October 1994 Page. 21
TROWEL TIPS
an aid to the masonry industry
Cleaning Masonry
Introduction
Cleaning is usually the last operation performed on newly constructed masonry. Unfortunately, it is sometimes performed as an afterthought, without proper planning or selection of cleaning procedures and techniques. Improper cleaning can virtually destroy the appearance and serviceability of new masonry. Usually, problems associated with the cleaning of masonry relate to: using the wrong kind of cleaning procedure for the specific masonry materials being cleaned, overcleaning in an attempt to compensate for poor workmanship during construction, or improper execution of recommended cleaning procedures. With careful planning, preparation, and application, these kinds of mistakes can be avoided and satisfactory cleaning accomplished.
Throughout the process, cleaning should be guided by the principle that "less is better"-meaning that it is better to underclean than overclean. Minor mortar smears and efflorescence associated with new masonry construction will often weather away as the building ages. In contrast, damage to the masonry from overcleaning can be virtually irreparable.
Planning
Attention to cleaning requirements should begin with preparation of the contract documents. Evaluate proposed cleaning procedures and techniques giving consideration to: the masonry materials used in the construction, the effect on adjacent materials (such as metal, wood, or glass), the logistics of the construction project, and any other site-specific factors that may affect the cleaning process. Next, perform the selected cleaning procedure(s) on a mock-up panel to verify suitability. The mock-up should be of the same materials intended for use in the construction and built with the level of workmanship expected on the project.
Acceptability of procedures selected based on evaluation of a mock-up should finally be confirmed on a trial section of the completed masonry before cleaning the whole project. The same individuals who will clean the entire masonry should first employ the proposed cleaning procedure on an inconspicuous area of the masonry. Not only will this step allow modification of the procedure to accommodate actual job conditions, but it will assure that all involved understand what is expected.
Materials
Mortar is usually the primary substance being cleaned from the face of masonry units in new construction. High-strength mortars (Type S and Type M mortars) are generally more difficult to remove than lower-strength mortars. Unfortunately most methods that will remove mortar from the face of masonry units will also remove mortar from the surface of mortar joints. This fact can result in significant deterioration of mortar joints during the cleaning operation, particularly when less labor-intensive procedures such as acid cleaning, high pressure spray cleaning, or abrasive cleaning are employed. Measures need to be taken to minimize the effect of the cleaning operation on the surface of mortar joints. Focus scrubbing efforts on unit surfaces, not mortar joint surfaces. If acid solutions are used, the mortar should be allowed to cure at moderate temperatures for about seven days prior to cleaning. Pressure water sprays should only be used with extreme caution. Keep pressure sprays moving over the masonry surface. Angle sprays to avoid hitting the surface of mortar joints with a perpendicular stream of water.
Note 1: The use of cleaning solutions (particularly acidic solutions), high pressure spray cleaning, and abrasive cleaning techniques require special safety precautions for workers (such as eye protection, protective gloves, and protective clothing) that are not discussed in this publication. Consult appropriate product labels, product information literature, and material safety data sheets for safety information on products and equipment used to clean masonry.
The principles involved in cleaning of masonry constructed using white or colored mortars are fundamentally the same as those for masonry using natural gray mortars. However, effects of cleaning on the appearance of mortar joints that are not noticeable in gray mortar joints may be strikingly obvious on a white or colored mortar joint. As noted above, cleaning procedures can remove the surface layer of a mortar joint. Often the cement paste is dissolved, leaving exposed sand particles at the surface of the mortar joint. In addition to creating a more porous joint surface, this can result in a significant change in the appearance - particularly if the sand color is significantly different from that of the cement paste. Overcleaning of masonry should always be avoided, but this is especially critical when