Technical Notes 20 Rev - Cleaning Brick Masonry
Nov. 1990 (Reissued March 2000)

Abstract: This Technical Notes addresses cleaning new buildings, removal of green (vanadium) and brown (manganese) stains, removal of stains from external sources and cleaning existing and historic buildings. Procedures included, if followed with good judgment, should result in successful applications of cleaning brick masonry.

Key Words: brick, cleaning, efflorescence, existing masonry, historic structures, new masonry, stains.

INTRODUCTION

The final appearance of a brick masonry wall depends primarily on the attention given to masonry surfaces during construction and the cleaning process. Many of the problems of brick masonry, brought to the attention of the Brick Institute of America over the past years, have resulted from improper cleaning methods. Some walls have been irreparably damaged as a result of a lack of attention to cleaning details and procedures.

Cleaning failures generally fall into one of three categories:

1. Failure to thoroughly saturate the brick masonry surface with water before and after application of chemical or detergent cleaning solutions. Dry masonry permits absorption of the cleaning solution and may result in "mortar smear", "white scum", or the development of efflorescence or "green stain". Saturation of the surface prior to cleaning reduces the absorption rate, permitting the cleaning solution to stay on the surface rather than be absorbed.

2. Failure to properly use chemical cleaning solutions. Improperly mixed or overly concentrated acid solutions can etch or wash out cementitious materials from the mortar joints. They have a tendency to discolor masonry units, particularly lighter shades, producing an appearance frequently termed "acid burn" and can also promote the development of "green" and "brown" stains.

3. Failure to protect windows, doors, and trim. Many cleaning agents, particularly acid solutions, have a corrosive effect on metal. If permitted to come in contact with metal frames, the solutions may cause pitting of the metal or staining of the masonry surface and trim materials, such as limestone and cast stone.

GENERAL

Before the actual cleaning of a project begins, all cleaning procedures and solutions should be applied to a sample test area of approximately 20 sq. ft. (1.9 m²). The effectiveness of the cleaning agent should be judged by inspection of the sample test area after a period of not less than one week after application. The size of the test area may be larger, depending upon the cleaning procedure. The indiscriminate use of muriatic acid or the wrong proprietary compound can cause unsightly, difficult-to-remove stains. Reactions of brick and cleaning solutions are not always predictable and thus it is safer to use a trial-and-error method on a small test area before committing the entire project to a set procedure. Minute quantities of certain minerals found in some fired clay masonry units and materials, such as manganese, added to color brick may react with some solutions and cause staining. Sample testing should be performed under conditions of temperature and humidity that will closely approximate the conditions under which the brickwork will be cleaned. Chemical cleaning solutions are generally more effective when the outdoor temperature is 50 ^oF (10 ^oC) or above.

It is always advisable for the mason to keep the brickwork as free from mortar smears as possible. However, in modern construction, where speed is important, even the most skilled of bricklayers may find this difficult. Some general precautions that can be taken to promote a cleaner wall are as follows:

1. Protect the base of the wall from rain-splashed mud and mortar splatter. Use straw, sand, sawdust, or plastic sheeting spread out on the ground, extending 3 to 4 ft. (0.9 to 1.2 m) from the wall surface and 2 to 3 ft. (0.6 to 0.9 m) up the wall.

2. Scaffold boards near the wall should be turned on edge at the end of the day to prevent possible rainfall from splashing mortar and dirt directly on the completed masonry.

3. Cover walls with a waterproof membrane at the end of the workday to prevent mortar joint wash out and entry of water into the completed masonry.

4. Protect site stored brick from mud. Store brick off the ground under protective covering.

5. Careful workmanship should be practiced to prevent excessive mortar droppings. Excess mortar should be cut off with the trowel as the brick are laid. Joints should be tooled when "thumbprint" hard. After tooling, excess mortar and dust should be brushed from the surface. Avoid any motion that will result in rubbing or pressing mortar particles into the brick faces. A medium soft bristle brush is preferable.

CLEANING NEW MASONRY

General

Table 1 should be referred to as a general cleaning guide for new masonry. Present cleaning methods for new masonry may be classified into three categories: 1) Bucket and Brush Hand Cleaning, 2) Pressurized Water Cleaning, and 3) Sandblasting. Some chemicals or chemical compounds used to clean brickwork and the resulting fumes may be harmful. Protective clothing and accessories, proper ventilation and safe handling procedures must be exercised. The use and disposal of some chemicals or chemical compounds are regulated by federal, state or local laws and should be researched before use. Manufacturer's material and handling requirements should be strictly observed.

Bucket and Brush Hand Cleaning

This is probably the most popular but most misunderstood of all the methods used for cleaning brick masonry. Its popularity is due to the simplicity of execution and the ready availability of proprietary cleaning compounds. A recommended general procedure using proprietary compounds, detergents or acid solutions is as follows:

1. Select the proper solution.

a. For proprietary compounds, make sure that the one selected is suitable for the brick and follow the cleaning compound manufacturer's recommended dilution instructions. Many proprietary cleaning solutions perform in a satisfactory manner for their intended cleaning jobs. However, their formulae are not generally disclosed and may be subject to change. It is suggested, therefore, that each product being considered be sample tested on a panel or inconspicuous wall area and judged on a trial basis before being used.

b. Detergent or soap solutions may be used to remove mud, dirt and soil accumulated during construction. A suggested solution is 1/² cup dry measure (0.14 L) of trisodium phosphate and 1/² cup dry measure (0.14 L) of laundry detergent dissolved in one gallon (3.9 L) of clean water.

c. For acid solutions, mix a 10% solution of muriatic acid (9 parts clean water to 1 part acid) in a non-metallic container. Pour acid into water. Do not permit metal tools to contact the acid solution. There is the temptation to mix acid solutions stronger than recommended in order to clean stubborn stains. The indiscriminate use of any acid solution may tend to cause further stains.

2. Schedule cleaning at least seven days after the brick masonry is completed. Mortar must be thoroughly set and cured. Prolonged time periods between the completion of the masonry work and the actual cleaning should be avoided when possible. Mortar smears and splatters left over a long period of time (6 months to 1 year) can cure on the wall surface and become very difficult to remove.

3. Remove larger mortar particles by hand with wooden paddles and non-metallic scrape hoes or chisels.

4. Protect metal, glass, wood, limestone and cast stone surfaces. Mask or otherwise protect windows, doors, and ornamental trim from cleaning solutions.

5. Presoak or saturate the area to be cleaned. Flush with water, from the top down. Saturated brick masonry will not absorb the cleaning solution or dissolved mortar particles. Areas below should also be saturated in order to prevent absorption of the run-off from above.

6. Starting at the top, apply the cleaning solution. Use a long handled stiff fiber brush or other type as recommended by the cleaning solution manufacturer. Allow the solution to remain on the brickwork 5 to 10 minutes. For proprietary compounds follow the manufacturer's instructions for application and scrubbing. Wooden paddles or other non-metallic tools may be used to remove stubborn particles. Do not use metal scrapers or chisels. Metal marks will oxidize and cause staining.

7. Heat, direct sunlight, warm masonry and drying winds will affect the drying time and reaction rate of cleaning solutions. Ideally, the cleaning crew should be working on shaded areas to avoid rapid evaporation.

8. Rinse thoroughly!! Flush walls with large amounts of clean water from top to bottom before they can dry. Failure to completely flush the wall of cleaning solution and dissolve matter from top to bottom may result in the formation of "white scum".

9. Work on a small area. The size of the "wash down" area should be determined after a trial run. This will permit the cleaning crew to examine work for initial results.

Pressurized Water Cleaning

To cut labor costs, many cleaning contractors utilize pressurized water. Some pressure systems feature a pressure gun and nozzle equipped with a control switch. This setup permits the operator to apply solutions to a wall over 100 ft. (30.5 m) from the base unit. Other systems have two separate hoses - one with plain water and the other with a cleaning solution. Low pressure has been defined as 100 to 300 psi (700 to 2100 kPa), medium pressure as 300 to 700 psi (2100 to 4850 kPa) and high pressure as 700 psi (4850 kPa) or greater. A sand finish or a surface coating may be removed by pressurized water cleaning, resulting in a different appearance. Nozzle pressure in excess of 700 psi (4850 kPa) may damage brick units and erode mortar joints.

Equipment should be as portable as possible. Units may be on wheels, skids, trailers, or pick-up truck beds. More elaborate systems include pumps, engines, acid containers, and water storage tanks fixed on truck beds.

Cleaning compounds used with this method should be compatible with the equipment. Some equipment manufacturers are careful to recommend that only specific cleaning compounds be pumped through their equipment. Others build pumps that will resist hydrochloric acid solutions for reasonable lengths of time.

The following procedure is suggested:

1. Select and test the cleaning solution on a sample area. Check the equipment for cleaning solution compatibility. For proprietary compounds, mix in accordance with the manufacturer's instructions.

2. - 5. Presoak wall. Same as steps 2 through 5 of Bucket and Brush Hand Cleaning method.

6. Application of cleaning solutions may be by a low pressure sprayer, 30 to 50 psi (200 to 350 kPa), or through the high pressure cleaning unit.

7. Permit the cleaning solution to remain on the wall for approximately 5 minutes.

8. Starting at the top, flush the wall down, as in the previous procedure.

Caution: It is possible for solutions to be driven into the masonry when applied under high pressure, and become the source of future staining. However, if the walls are sufficiently saturated with water before the solutions are applied, the risk of penetration is reduced. Experience has shown that this cleaning method has a high probability of changing the appearance of sand molded brick, sand- faced extruded brick, and brick with glazed coatings or slurries applied to the finished faces. The brick manufacturer should be consulted on the use of high pressure water cleaning of such brick.

Sandblasting

Dry sandblasting has been around for many years and is one method that may be used to clean brick masonry. However, there is also the possibility that, through improper execution, the face of brick units and mortar joints may be scarred. This method is sometimes preferred over conventional wet cleaning since it eliminates the problem of chemical reaction with vanadium salts and other materials used in manufacturing brick. Light and heavily sanded, coated, glazed and slurry finished brick should not be cleaned by sandblasting.

Sandblasting by a qualified operator, in conjunction with proper specifications and job inspection, can be satisfactory. Basically, it involves a portable air compressor, blasting tank, blasting hose, nozzle, and protective clothing and hood for the operator. The air compressor should be capable of producing 60 to 100 psi (400 to 700 kPa) at a minimum air flow capacity of 125 cu ft. (3.5 m³) per minute. The inside orifice or bore of the nozzle may vary from 3/16 to 5/16 in. (4.8 to 7.9 mm) in diameter. The sandblast machine (tank) should be equipped with controls to regulate the flow of abrasive materials to the nozzle at a minimum rate of 300 lb/h (0.004 kg/s).

There are various degrees of cutting or cleaning desired and consequently many types of abrasive materials. They may be of mined silica sand, crushed quartz, granite, white urn sand (round particles), crushed nut shells, and other softer abrasives. Mined silica sands and crushed quartz should have a hardness of approximately 6 on Moh's Scale and be a Type "A" or "B" gradation. See Table 2.

A suggested procedure for sandblasting is as follows:

1. Select sandblast materials that are clean, dust free and abrasive.

2. Brick masonry should be dry and well cured.

3. Remove all large mortar particles, as in previous methods.

4. Protect non-masonry surfaces adjacent to cleaning areas. Use plastic sheeting, duct tape or other covering materials.

5. Test clean several areas at varying distances from the wall and several angles that afford the best cleaning job without damaging brick and mortar joints. Workmen should be instructed to direct abrasive at the units and not on the mortar joints.

TABLE 2
Typical Screen Analysis for Sandblasting Sand Abrasives^a

^aThe screen analysis listed above is suggested primarily for mined silica sands and crushed quartz. Reference source: "Good Practice for Cleaning New Brickwork", produced by the Brick Association of North Carolina, 822 N. Elm St., Greensboro, NC 27415.

^bType "A" gradation is suggested for very lightly soiled brick masonry or where very light, fine texturing of the masonry surface is permitted.

^cType "B" gradation is suggested for heavy mortar stains, or where a medium texturing of the masonry surface is permitted.

REMOVING EFFLORESCENCE

The removal of efflorescent salts is relatively easy compared to some other stains. Efflorescent salts are water soluble and generally will disappear of their own accord with normal weathering. This is particularly true of "new-building bloom". White efflorescent salts can be removed by dry brushing or with clear water and a stiff brush. Heavy accumulation or stubborn deposits of white efflorescent salts may be removed with a proprietary cleaner. It is imperative that the wall be saturated before and after the solution is applied. Refer to Technical Notes 23 Series for more information on the cause and prevention of efflorescence.

REMOVING "GREEN STAIN" (VANADIUM SALTS)

Brick units can develop yellow or green stains resulting from vanadium salts. These stains can be found on red, buff or white brick. The vanadium salts responsible for these stains originate in the raw material used to manufacture certain brick units.

As water travels through the brick, it dissolves the vanadium oxide and sulfates. Chloride salts of vanadium require highly acidic leaching solutions and are usually the result of washing brick masonry with acid solutions. Thus, the problem incurred with "green staining" often does not exist until the brickwork is washed down with an acid solution. For further information on "green stain" refer to Technical Notes 23 Series.

To minimize the occurrence of green stain:

1. Store brick off the ground under protective covering.

2. Do not use acid solutions to clean light colored brick.

3. Follow the recommendations of the brick manufacturer for the proper cleaning compounds and procedures.

Should the brickwork have been cleaned with an acid solution and "green staining" appears, the following procedure may be followed to neutralize the acid:

1. Immediately following the acid wash, flush brickwork with water.

2. Wash or spray the brickwork with a solution of potassium or sodium hydroxide, consisting of 1/2 lb (0.23 kg) hydroxide to 1 qt (0.95 L) water or 2 lb (0.91 kg) per gal (3.79 L). Allow this to remain for two or three days.

3. Use a hose to wash off the white salt remaining on the brickwork from the hydroxide.

Various proprietary cleaning compounds have been developed to remove "green stain". Their effectiveness on a particular wall can only be determined by test.

REMOVING "BROWN STAIN" (MANGANESE STAIN)

Under certain special conditions this stain may occur on mortar joints of brickwork containing manganese colored units. It appears as a tan, brown, nearly black, or sometimes gray colored stain. The "brown stain" has an oily appearance and may streak down over the face of the brick. It appears to be running down from the brick-mortar interface and is the result of manganese used in some brick as a coloring agent. When the solution reaches the mortar joints, the salts are deposited upon neutralization by the cement or lime. See Technical Notes 23 Series.

During firing in the manufacturing process of some brick, manganese coloring agents experience several chemical changes. This results in compounds that are not soluble in water, but are soluble in weak acid solutions. Since brick can take up acid by absorption, such weak acid solutions can prevail in brick washed with hydrochloric acid. Rainwater may also be acidic in some industrialized areas.

To minimize this problem, do not use any acidic solutions on tan, brown, black or gray brick. There are special proprietary cleaning compounds available for cleaning brick containing manganese. These may be tested for effectiveness. The advice of the brick manufacturer should be requested and followed.

The permanent removal of manganese stain may be difficult. After initial removal it often returns. The following method has been effective in removing "brown stain" and preventing its return.

1. Carefully mix a solution of acetic acid (80% or stronger), hydrogen peroxide (30-35%) and water in the following proportions by volume: 1 part acetic acid, 1 part hydrogen peroxide, and 6 parts water. Caution: Although this solution is very effective, it is a dangerous solution to mix and use. Acetic acid-hydrogen peroxide may also be available in a premixed form known as peracetic acid. This acid, a textile chemical, is also dangerous and may be difficult to purchase.

2. After wetting the brickwork, brush or spray on the solution. Do not scrub. The reaction is usually very rapid and the stain quickly disappears. After the reaction is complete, rinse the wall thoroughly with water.

An alternate solution suggested for new and light colored "brown stains" is oxalic acid crystals and water. Mix 1 lb of crystals (0.45 kg) to 1 gal (3.79 L) of water. There are also proprietary compounds formulated to remove "brown stains". Their effectiveness should be judged only after testing.

Proprietary compounds have been used and sometimes found to be effective in keeping the stain from re-appearing. Consult the recommendations and directions of the cleaning solution or brick manufacturer when applying proprietary solutions to remove manganese stains.

REMOVAL OF EXTERNALLY CAUSED STAINS

General

These are stains caused by external materials being spilled, splattered on, and absorbed by the brick. Each is an individual case and must be treated accordingly.

A large number of external stains can be removed by scrubbing with kitchen cleanser. Others can frequently be removed by bleaching with a household bleach. A combination, such as is found in some kitchen cleansers, may prove most effective. Table 3 lists sources of some materials suggested for this use.

TABLE 3

Sources of Cleaning and Masking Agents^a

^aWarning: Some chemicals and resulting fumes may be harmful. Protective clothing and accessories, proper ventilation and safe handling procedures must be exercised. The use and disposal of some chemicals are regulated by federal, state or local laws and should be researched before use.

Poultice

The use of a poultice is included in some of the recommendations that follow. A poultice is a paste, made with a solvent or reagent and an inert material. It works by dissolving the stain and leaching or pulling the solution into the poultice. The powdery substance is simply brushed off when dry. Repeated applications may be necessary. Poultices tend to prevent the stain from spreading during treatment and to pull the stain out of the pores of the brick. Poultices are normally used only for small stain spots.

The inert material may be talc, whiting, fuller's earth, diatomaceous earth, bentonite or other clay. The solution or solvent used will depend upon the nature of the stain to be removed. Enough of the solution or solvent is added to a small quantity of the inert material to make a smooth paste. The paste is smeared onto the stained area with a trowel or spatula and allowed to dry. When dried, the remaining powder is scraped, brushed or washed off.

If the solvent used in preparing a poultice is an acid, do not use whiting as the inert material. Whiting is a carbonate which reacts with acids to give off carbon dioxide. While this is not dangerous, it will make a foamy mess and destroy the power of the acid.

Paint Stains

For fresh paint, apply a commercial paint remover, or a solution of trisodium phosphate in water at the rate of 2 lb. (0.91 kg) of trisodium phosphate in 1 gal (3.79 L) of water. Allow to remain and soften the paint. Remove with a scraper and a stiff bristle brush. Wash with clear water. There are also commercial paint removers in the form of a gel solvent. These should be applied on a small test area on a trial basis. For very old dried paint, organic solvents similar to the above may not be effective, in which case the paint must be removed by sandblasting or scrubbing with steel wool.

Iron Stains

Iron stains are quite common and, in some cases, cover large areas. These stains are easily removed by spraying or brushing with a strong solution 1 lb (0.45 kg) of oxalic acid crystals per gal (3.79 L) of water. Ammonium biflouride added to the solution 1/2 lb (0.23 kg) per gal (3.79 L) will speed up the reaction. The ammonium biflouride generates hydroflouric acid, a very dangerous material, which can etch the brick and glass. Etching will be evident on very smooth brick. Therefore, use this solution only with caution.

Alternate method. Mix 7 parts lime-free glycerine with a solution of 1 part sodium citrate in 6 parts lukewarm water, and mix with whiting or diatomaceous earth to make a poultice. Apply a thick paste on stain with trowel. Scrape off when dry. Repeat until stain has disappeared and wash thoroughly with clear water. A poultice made from a solution of sodium thiosulfate and an inert powder (talc) has also been used for the removal of iron rust stain.

Copper or Bronze Stains

Mix together in dry form 1 part ammonium chloride (sal ammoniac) and 4 parts powdered talc. Add ammonia water and stir until a thick paste is obtained. Place this over the stain and leave until dry. When working on glazed brick use a wooden paddle to remove the paste. An old stain of this kind may require several applications. Aluminum chloride is sometimes used in the above procedure instead of the sal ammoniac.

Welding Splatter

A problem related to iron staining is welding splatter. When metal is welded too close to a pile of brick or completed brickwork, some of the molten metal may splash onto the brick and melt into the surface. The oxalic acid-ammonium biflouride mixture, recommended for iron stains, is particularly effective in removing welding splatters.

Scrape as much of the metal as possible from the brick. Apply the solution in a poultice. Remove the poultice when it is dried. If the stain has not disappeared, use sandpaper to remove as much as possible and apply a fresh poultice. For stubborn stains, several applications may be necessary.

Smoke

Smoke is a difficult stain to remove. Scrub with scouring powder (particularly one containing bleach) and a stiff bristle brush. Some alkali detergents and commercial emulsifying agents, brush or spray applied, given sufficient time to work, also perform well. They should be tested on a small area, before use on a large area. They have the added advantage that they can be used in steam cleaners. For small, stubborn stains, a poultice using trichloroethylene will pull the stain from the pores. Exercise caution when using trichloroethylene in confined spaces. Ventilate the fumes.

Oil and Tar Stains

Oil and tar stains may be effectively removed by commercial emulsifying agents. For heavy tar stains, mix the agents with kerosene to remove the tar, and then water to remove the kerosene. After application, they can be hosed off. When used in a steam cleaning apparatus, they have been known to remove tar without the use of kerosene.

Where the area to be cleaned is small, or where a mess cannot be tolerated, a poultice using naphtha or trichloroethylene is most effective in removing oil stains.

Also, dry ice or compressed CO2 may be applied to make tar brittle. Light tapping with a small hammer and prying with a putty knife generally will be enough to remove thick tar splatters.

Dirt

Dirt is sometimes difficult to remove, particularly from a textured brick. Scouring powder and a stiff bristle brush are effective if the texture is not too rough. Scrubbing with an oxalic acid-ammonium biflouride solution, recommended for iron stains, has proven effective on some moderately rough textures. For very rough textures, pressurized water cleaning appears to be a most effective method.

Straw and Paper Stains

Straw and paper stains sometimes result from wet packing materials. Not all packing materials stain brick, but those that do can produce very stubborn stains. Such stains can be removed by applying household bleach. Allow time to dry. Several applications may be required before the stains disappear. The solution of oxalic acid-ammonium biflouride, recommended for iron stain, cleans the stain much more rapidly.

Plant Growth

Occasionally an exterior masonry surface, not exposed to sunlight, remains in a constantly damp condition, thus exhibiting signs of plant growth, i.e., moss. Application of ammonium sulfamate or weed killer, in accordance with directions furnished with the compound, has been used successfully for the removal of such growths.

Ivy

Avoid pulling the vines away from the masonry since this may damage the brick or mortar. Carefully cut away a few square feet of vine in an inconspicuous area and examine how much they have rooted into the brickwork. Inspect the exposed area for condition and appearance. There will be some deposits left on the masonry. These are the "suckers" that attached and held the vines. Do not use acids or chemicals to remove the suckers. Leave in place until they dry and turn dark. Remove with a stiff bristle brush and detergent.

Egg Splatter

Brick walls vandalized with raw eggs have been successfully cleaned with a saturated solution of oxalic acid crystals dissolved in water. Mix in a non-metallic container and apply with a brush after saturating the surface with water.

White Scum

White scum is a grayish-white haze on the face of brick. It is sometimes mistaken for efflorescence, but technically is silicic acid scum. This condition results from the failure to saturate the wall before application or thoroughly rinsing acid solutions after cleaning. Generally, it is a film of material that is insoluble in acid solutions except for hydroflouric acid, which is very dangerous and not generally recommended for this use. Proprietary compounds formulated to remove this condition may be tested and their effectiveness judged.

If removal is too difficult, masking of the haze may be considered. In time, weathering will remove both the masking solution and white scum.

Masking solutions may consist of paraffin oil and Varsol, or linseed oil and Varsol, applied by brush to the affected brick units. Linseed oil and Varsol (10-25% linseed oil) or paraffin oil and Varsol (2 to 50% paraffin oil) will darken light colored brick. Several batches of solutions with various concentrations should be mixed and tested. Generally, solutions of 2 to 25% paraffin oil will be satisfactory. Allow 4 to 5 days of warm drying weather to pass, preferably at 70°F (21°C) minimum, before a judgment is made on the effectiveness of the solutions.

Stains of Unknown Origin

Stains of unknown origin can be a real challenge. Laboratory tests of unknown stains maybe necessary to determine their composition. Then the appropriate method may be implemented to clean the brickwork. The indiscriminate use of any cleaning agent may aggravate the initial stain and cause further staining. The application of a cleaning agent without identifying the initial stain may result in other stains which are difficult to remove. However, appearance of the stain may be the first clue.

Rust-colored stains may actually be rust. Such stains are quite common and have been known to come from mortar ingredients, wall ties or joint reinforcement with inadequate cover, welding splatter on the brick, or something placed on the pile of brick prior to being laid in the wall.

"Green stains" may be grass, moss or vanadium efflorescence. "Brown stains" may also be vanadium efflorescence, or possibly manganese staining.

One test useful in narrowing down the list of possible causes of a stain involves a substance ordinarily not placed on brick masonry. Concentrated sulfuric acid in contact with an organic material, will turn it black. This is a quick and easy way to identify stains originating from such a material. Organic stains can usually be removed with household bleach or oxalic acid.

CLEANING EXISTING MASONRY

The paper, "Cleaning Masonry - A Review of the Literature", by Clayford T. Grimm, lists various methods of cleaning exterior masonry walls. They are: high-pressure steam, sandblasting, hand washing, pressurized water and chemicals with steam.

High-Pressure Steam

This method lends itself readily and satisfactorily to various types of masonry and is generally not injurious to most masonry surfaces. Buildings with smooth hard brick or brick with glazed surfaces should always be cleaned with steam. The more impervious a brick unit, the easier it should clean. Steam cleaning without chemical additives is usually at pressures less than 60 psi (400 kPa).

In most cases, buildings may be cleaned satisfactorily with plain high-pressure steam. For stains it is sometimes necessary to use a chemical or detergent solution.

Sandblasting

The dry method of sandblasting should be employed only when brick will not be damaged and when certain types of brick cannot be successfully cleaned with high-pressure steam. See the section on Sandblasting under Cleaning New Masonry.

Wet Sand Cleaning

The wet sand cleaning method is used on hard brick and depends on a water-cushioned abrasive action for its effectiveness. It is suggested for removal of paint or other surface coatings, where abrasion of the surface is permissible. Wet sand cleaning employs water in the cleaning action to eliminate dust.

Wet Aggregate Cleaning

The wet aggregate cleaning method is a special process for use on soft brick and soft stone materials, and is particularly effective on surfaces with flutings, carvings and other ornamentation. It is a gentle but thorough process, employing a mixture of water and a friable aggregate free from silica, delivered at low pressure through a special nozzle with a "scouring" action which cleans effectively without damage to the surface.

Hand Washing

Many buildings of smaller size have been cleaned successfully by hand washing. It is a bit slower method and does not give the added advantage of heat as in high-pressure steam. Usually this work is done by using soap or detergent with cold water. The method is generally more costly because it is slower, does not lend itself to a job of any size, and may need to be repeated more often. See the section on Bucket and Brush Hand Cleaning.

High-Pressure Cold Water

This method usually results in a satisfactory job. An ample water supply is necessary. However, disposing of large volumes of water used is sometimes a problem.

On hard burned brickwork, water at very high pressure can be effective but requires careful application by experienced operators. Pressure should not exceed that which would damage the brickwork being cleaned. Nozzle pressure in excess of 700 psi (4850 kPa) can damage brick and mortar joints.

Chemicals and Steam

Mr. Grimm points out that chemicals and high-pressure steam are used primarily to remove applied coatings to masonry, such as paint. This is a highly specialized field and frequently the proper cleaning agent can be determined only after an analysis of the various factors involved in a particular project.

CLEANING HISTORIC STRUCTURES

This type of cleaning endeavor should be referred to a restoration specialist. There are comprehensive papers and publications available on the subject of restoration. Before an old structure is to be cleaned, several questions should be asked before making a final decision, such as: (1) Why clean?, (2) What is the dirt? and (3) What is the construction of the building?

The query "Why Clean?" is posed in the publication "The Cleaning and Waterproof Coating of Masonry Buildings" - Preservation Briefs No. 1, by Robert C. Mack, AIA.

SUMMARY

Cleaning brick masonry still remains, for the most part, a trial-and-error procedure. Therefore, it is strongly suggested that any cleaning procedure and chemical cleaning solution be tested as suggested in this Technical Notes. Such testing should be performed under conditions of temperature and humidity that will closely approximate those conditions under which the brick masonry will be cleaned. Cleaning compounds recommended by the brick or cleaning agent manufacturer should also be trial tested before being committed to the entire project.

If general suggestions and recommendations contained in this Technical Notes are followed with good judgment and common sense, successful cleaning of brick masonry should be possible and practical. Due to the diverse nature of cleaning solutions, procedures and problems, the Brick Institute of America cannot accept responsibility for the final success or effectiveness of these procedures.

In conclusion, nothing is quite as effective as careful attention exercised during construction to keep brick walls relatively clean. If this is successful, it will eliminate the need for costly cleaning procedures.

REFERENCES

More detailed information on subjects discussed here can be found in the following publications:

1. Grimm, C.T., "Cleaning Masonry - A Review of the Literature", Construction Research Center, University of Texas at Arlington, 1988.

2. Mack, R.C., "The Cleaning and Waterproof Coatings of Masonry Buildings", Preservation Briefs No. 1, National Park Service, Washington, D.C., 1975.