Along with qualities like structural strength, longevity, fire resistance, acoustic performance, and low maintenance, concrete masonry buildings are incredibly beautiful. The beauty of concrete masonry can be maintained with proper cleaning both during construction and over the building’s lifetime.
A well-designed and built masonry wall requires very little upkeep, although impurities can take away from an otherwise appealing structure. It is typically necessary to clean up mortar stains, construction dirt, and potentially efflorescence from the building period. Throughout the building’s life, additional cleaning can be necessary to remove atmospheric grime and soot or discoloration from certain sources. Contaminants can be eliminated and a more consistent appearance can be achieved with proper cleaning.
Several general cleaning techniques that are relevant to whole-wall cleaning are covered in this TEK. See Removal of Stains From Concrete Masonry, TEK 08-02A (ref. 7) for details on how to get rid of stains or localized impurities.
SUBSTRATES
The concrete masonry units and mortar used in a masonry wall might have an impact on how easy it is to clean. Cleaning supplies and methods that work for one brick wall might not work for another. Additionally, walls that combine multiple materials—like a concrete masonry wall with clay masonry banding—should be given extra thought.
Units of Concrete Masonry
A thin layer of cement paste created by the usual concrete masonry manufacturing process gives conventional, or nonarchitectural, concrete masonry units (CMUs) a comparatively smooth surface. This layer may be removed by aggressive cleaning techniques, exposing aggregate and changing the finished look. For a consistent appearance after cleaning, any vigorous cleaning should be carried out consistently over the whole wall surface. Sometimes smooth-faced units are requested for pressure chemical or abrasive cleaning in order to create a somewhat mottled “stone washed” look.
After being manufactured, ground-faced units—also known as honed or burnished units—are polished to produce a smooth surface that resembles polished natural stone. Frequently applied to enhance color, coatings can aid in cleaning by keeping dirt and other impurities from soaking into the surface. During construction, every attempt should be taken to keep the ground-faced units clean and clear of mortar stains and droppings. After a thorough cleaning, these units can be resealed if necessary.
The texture of other architectural CMUs, like split faced, split fluted, and tumbled units, is created during manufacturing and resembles genuine stone. These units are more tolerant of mild efflorescence or other discolorations because of their rough texture, which tends to conceal small soiling. Additionally, if abrasive cleaning is necessary, this texture is better suited for it.
A permanent colored face, usually made of polyester resins, silica sand, and other chemicals, is bonded to a concrete masonry unit to create glazed concrete masonry units. A smooth, impermeable surface that is extremely stain-resistant and cleanable is the end product. Smears and droppings from mortar and grout should be removed during construction while they are still easily removable to prevent them from fully solidifying to the surface.
Because mortar tends to blend in, choosing a color that is similar to the concrete masonry unit makes it easier to remove mortar smears off the wall. Because smooth or ground-faced units can be challenging to clean without changing their appearance, mortar color should be chosen to match the color of the unit. More vigorous cleaning may be necessary to get rid of visible mortar on walls with contrasting mortar and masonry unit colors.
Generally speaking, it is best to specify the lowest-strength mortar that will satisfy project requirements. It is not always the case that mortars with higher compressive strengths and higher cement contents function better in the field; in fact, the contrary is more frequently true. Compared to stronger mortars, mortars with lower compressive strengths are typically easier to remove off the wall’s face. Additionally, lower strength mortars are more workable, which tends to improve construction quality. Keep in mind that certain mortars may not be allowed for use in specific situations due to building codes. TEK 09-01A, Mortars for Concrete Masonry (ref. 4) contains more thorough information about masonry mortars.
Cleaning while building
By using appropriate design, building, and maintenance techniques, many stains can be avoided or reduced. The amount of cleaning needed for a freshly built wall can be significantly impacted by construction methods. For instance, using the right grouting techniques can help avoid grout blowouts and the cleanup that goes along with them. When building is finished, less forceful cleaning techniques may be possible if the masonry is kept as dry and clean as possible.
Controlling efflorescence, mortar and grout stains, and efflorescence are all part of cleaning exposed concrete masonry during construction. Control and Removal of Efflorescence, TEK 08-03A (ref. 1), provides comprehensive details on construction methods that reduce efflorescence. Recommendations for reducing mortar and grout stains during construction include the following (refs. 3, 6):
- The trowel’s edge should be used to chop off mortar that has been forced out of mortar joints during unit placement. Take care not to let the mortar fall onto the wall surface or smear it as it does.
- After the mortar has first set, it should be removed if it does land on or smear the concrete masonry unit. It is best to trim and clean walls before erecting scaffolding.
- Especially on split-faced units, wait until the mortar is thumbprint hard before cutting off the mortar tags. Joints should also not be tooled until the fingerprint is hard.
- Once allowed to dry, mortar droppings that stick to the units’ exposed faces can be scraped off using a trowel or chisel. A firm fiber or bristle brush can next be used to remove any leftover mortar.
- Scaffolding should occasionally have excess mortar removed.
- Spills of grout should be cleaned up right away by brushing and washing.
- Spreading plastic sheets 3 to 4 feet (914 to 1,219 mm) on the ground next to the wall and 2 to 3 feet (609 to 914 mm) up the wall face will shield the base of the wall from mud splashing and mortar and grout droppings.
- In addition to these suggestions, freshly built brickwork should be shielded from any splatters or other stains caused by nearby building activities. For instance, when concrete is poured close by and a curing chemical is sprayed, plastic should be placed over the brickwork.
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