Cleaning procedure for concrete walls. 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.
Cleaning procedure for concrete walls. 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.
Cleaning procedure for concrete walls. 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 procedure for concrete walls. 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.
Cleaning procedure for concrete walls. THE CLEANING PROCEDURE PLAN
Depending on the kind of contamination and the intended outcome, the cleaning solution and process should be carefully considered. In order to properly clean the wall, the least forceful cleaning technique should be used. Make sure the mortar joints have dried before cleaning to prevent harm from the cleaning process.
Cleaning techniques can change how the completed masonry looks; usually, the units’ surfaces have at least some cement paste removed. More aggregate is seen as a result, which may change the hue. Generally speaking, the more aggressive the cleaning technique, the more paste is eliminated and the more likely it is that the wall’s appearance will change. Sandblasting, for instance, is likely to change the appearance more than hand cleaning with water and soap. Additionally, keep in mind that depending on the particular steps taken, the same cleaning technique may provide varied outcomes. Results from lesser pressure sandblasting will differ from those from higher pressure sandblasting. Once more, the least harsh cleaning technique that will be satisfactory should be selected.
To evaluate the cleaning chemical and processes’ efficacy for the type of pollutant being removed, their potential impact on the final masonry’s appearance, and the agreed-upon level of cleanliness, they should first be applied to a sample panel or discrete area. To assess the outcomes after cleaning, the sample panel should be viewed in diffused lighting from a distance of 20 feet (6,096 mm).
To maintain a consistent appearance, it is crucial that all of the masonry be cleaned using the same technique, regardless of the cleaning method that is selected. This includes the dilution rate, brushing/scraping method, dwell duration, reapplication, rinse procedure, etc. In a similar vein, it’s important to avoid cleaning regions that overlap because this could also result in an uneven appearance.
Materials that could be harmed by contact with certain stain removers or by physical cleaning techniques include glass, metal, wood, architectural concrete or concrete masonry, and any landscaping that is close to the area that needs to be cleaned. The recommendations of the cleaning agent manufacturer should be followed since the cleaning procedure affects the area that needs protection and the degree of protection.
To reduce additional moisture absorption or soiling, a surface water repellent should be placed as soon as conditions permit after the wall has been cleaned.
Cleaning procedure for concrete walls. Methods of Cleaning
Concrete masonry cleaning techniques can be broadly categorized into four groups: chemical, abrasive, water, and hand cleaning (ref. 2). To determine the impact of cleaning, a sample panel or an unnoticed area of the building should be cleaned using any technique.
Cleaning Your Hands
During building, basic hand tools like a trowel, chisel, fiber brush or stiff bristle brush, abrasive block, or a shattered piece of masonry are used for cleaning. Because steel-wire brushes can leave behind metal particles that could rust and discolor the stonework, they should not be utilized.
Cleaning of Water
Scrubbing with water and detergent, soaking in water, steam cleaning, or pressure washing are all examples of water cleaning. The least amount of water necessary to thoroughly clean the wall should be utilized when employing water cleaning techniques because any water that seeps into the wall could encourage efflorescence. For further information, see Control and Removal of Efflorescence, TEK 08-03A (ref. 1).
Scrubbing unpainted walls with water and a tiny bit of detergent is typically sufficient. This cleaning technique is non-aggressive and usually doesn’t change the look of the stonework. However, because of the labor required, it might not be economical for vast regions.
First, use a dry brush to remove any clay or debris. Because any metal particles left on the stone surface could corrode and discolor it, steel-wire brushes should not be used. It is better to use nonmetal brushes like nylon or stiff fiber. Dirt deposits enlarge when soaked in water, which weakens their hold on the brickwork underneath and makes it possible for water to wash them away. Again, if efflorescence is the main issue, this approach might not be suitable.
In chilly weather or on oily surfaces, heated water is helpful. Warm water should not, however, be utilized with alkaline substances at temperatures higher than 160° F (71° C). Using hot water with acid cleansers has no discernible benefits (ref. 2).
In order to avoid the use of harsh chemicals, pressure washing equipment is frequently selected for masonry restoration projects. It can be effective for surface cleaning. Minimal water pressure is necessary to prevent water from being forced into the wall, which might result in efflorescence. Keep in mind that high pressures might change the final appearance or harm stonework. The most consistent results will be obtained by applying a constant pressure and keeping a predetermined distance from the wall. When using high pressure cleaning, it is advised that:
The pressure must be kept between 400 and 600 psi (2.76 and 4.14 MPa); the flange tip must be wide rather than pointed; the tip must be maintained at least 12 inches (305 mm) from the masonry surface; and the spray must be directed at a 45-degree angle to the wall rather than perpendicular to it. Scrubbing can also be combined with pressure washing. Brush application produces a moderate agitation that enhances overall cleaning outcomes and allows for minimal rinsing pressure.
Pressure washing has essentially replaced steam cleaning. However, the effect of softening and loosening oil and dirt particles is enhanced by adding heat to the water, making it easier to rinse them away. Depending on the apparatus, steam is typically produced in a flash boiler and directed against the wall with a wand at pressures ranging from 10 to 80 psi (69 to 552 kPa). Steam cleaning is slower than pressure washing, but it is less forceful.
Cleaning using Chemicals
There are numerous proprietary cleaning solutions for concrete masonry; for suggested appropriate products, contact the maker of the concrete masonry. Many possible issues, including those related to combining reactive compounds, are avoided when using premixed chemicals. Additionally, they are combined in the right amounts for safe application on brickwork. To safeguard the user and the brickwork, as well as to prevent any potentially hazardous discharge, strict attention to the manufacturer’s instructions is necessary.
Chemical surfactants aid in the dissolution of impurities so they can be removed during the last rinse when used with water washing methods. The surfaces to be cleaned must be thoroughly prewetted with low water pressure (maximum 30 to 50 psi, 207 to 345 kPa) before using chemical cleaning agents. The cleaning agents must be diluted according to the manufacturer’s instructions, and the application pressures should be maintained to a minimum.
After the cleaning chemical has been applied, the wall should be thoroughly rinsed with fresh water, preferably at moderate pressure but if necessary at high pressure, using the precautions outlined in the Water Cleaning section.
Although chemical cleaning is frequently more successful and economical than pressure washing, it might be a more forceful technique. Although this process can alter the final appearance of the wall, when done correctly, the effects are consistent throughout the wall. Use soft-fibered brushes or a low pressure spray (less than 50 psi, 345 kPa) to apply chemical cleaning solutions.
Concrete masonry can be cleaned with chemical cleaning solutions without causing surface damage; do not use undiluted or uncooked acids. Because acids erode the cement matrix at the masonry surface and can harm any inherent water repellant at the surface, even diluted acids should be used carefully and only after the wall has been completely prewetted. This alters the masonry’s color and texture by making the face more porous and exposing more aggregate. Acids can also lessen the water repellency at the surface of masonry that has an integrated water repellent. Applying acids under pressure is never advisable. Generally speaking, a cleanser should be regarded as acidic if its pH is less than 4 or 5. Furthermore, extremely alkaline products need to be thoroughly rinsed and neutralized with an acidic afterwash; efflorescence may be an undesirable consequence if alkali is still present.
Cleaning with BETOFF-B liquid
This innovative preparation will easily clean any concrete wall or concrete surface. Just apply it, spread it with a soft-bristled brush, and then wash off all the dirt with water. It’s so simple and so effective!
Cleaning with Abrasive
The most extreme cleaning technique is abrasive cleaning, which aims to remove the outer layer of the masonry where the stain is placed rather than washing away surface impurities. Because of this, ground-faced units, whose surfaces are polished and smooth, shouldn’t utilize it. The term “abrasive cleaning” usually refers to grit blasting, sometimes known as “sandblasting,” even though it encompasses techniques including grinding wheels, sanding discs, and sanding belts. Because silica sand is considered an irritant, its usage is limited in some places; nevertheless, there are numerous alternative blasting media that can be used.
Sandblasting can be done in cold weather because it is a dry procedure that won’t encourage efflorescence. With the right approach, the cleaning procedure yields a consistent outcome throughout the wall, just as pressure chemical cleaning.
When using abrasive cleaning methods, caution is necessary because excessive use can significantly alter the masonry’s durability, look, and watertightness. By exposing aggregate or roughening the surface, sandblasting can change the masonry’s look. With split-faced units, this is less of an issue. Because sandblasting increases surface porosity, it can sometimes hasten degradation. When considering sandblasting, pretesting with a sample panel is essential.
Softer abrasives
Softer abrasives like crushed corn husks, walnut shells, or glass or plastic beads can be used to reduce possible harm. This method, commonly referred to as micro-peening, is slower, more expensive, and typically not suitable for extensive cleaning projects.
Wearing protective clothes and gear, such as an authorized respirator under a hood, is required. Water is added to the air-grit stream at the nozzle to remove the majority of the dust that comes with a dry sandblasting operation. The same safety gear and clothes are required as for the dry process since the smaller particles still pose a health risk. Rinsing down the cleaned surface after blasting is an additional step required by the wet method.
Any water-resistant surface coatings that have been previously applied must be redone following abrasive cleaning since sandblasting eliminates them.
FINAL RESULTS
Concrete masonry modules come in a range of finishes, such as glazed, split-faced, and ground-faced. The usually appealing appearance of concrete masonry buildings can be tarnished by contaminants from the atmosphere after years of exposure and from the construction process, such as mortar streaks. Cleaning techniques that have proven successful include abrasive blasting, water, chemical treatments, and manual cleaning. Certain CMU manufacturers offer cleaning advice; in other situations, a qualified expert may be able to offer guidance on the most effective cleaning techniques. Cleaning supplies and methods are tested in the field to help guarantee the intended outcomes.
