Home / Technical Resources / stain removal

Resources

Control and Removal of Efflorescence

August 2018

INTRODUCTION

Efflorescence is a deposit of soluble salts and bases, usually white in color, that sometimes appear on the surfaces of masonry or concrete construction. Although it may be an aesthetic concern, efflorescence will not affect structural performance.

Often efflorescence is apparent just after the structure is completed. If the efflorescence is essentially uniform throughout the exterior facade, it indicates normal water loss from the materials and the building. Some identify this occurrence as “early age” efflorescence or “new building bloom”. If unattended, the salts will eventually be removed by rain water.

If the deposit is heavy and essentially shows as white streaks immediately below mortar joints or covering localized areas of the masonry, it indicates that water has entered or is entering the wall at a higher elevation. These salts are called leachates, referred to “lime spots”, “lime runs” and “lime deposits”; and are sometimes identified as “late age” or recurrent efflorescence. Late age or recurrent efflorescence usually consists of more permanent surface accumulations and indicates a need for corrective measures.

This TEK discusses the various mechanisms which cause efflorescence and presents recommendations for its control and removal.

CAUSES OF EFFLORESCENCE

A combination of circumstances causes efflorescence. First, there must be soluble compounds in the masonry. Second, moisture must be present to pick up the soluble salts and carry them to the surface. Third, some force—evaporation or hydrostatic pressure—must cause the solution to move. If any one of these conditions is eliminated, efflorescence will not occur.

Source of Salts

The individual elements and compounds associated with efflorescence may be present in concrete masonry units, mortar and grout. However, efflorescence of masonry is generally attributed to water soluble sodium, potassium and calcium.

These solutions either precipitate as hydroxides or combine with atmospheric carbon dioxide and sulfur trioxide. The compounds produced by the combination of these elements are white or yellow salts, all of which are less water soluble than their former hydroxide counterparts. Chlorides are usually a result of contamination of masonry units and sand by sea water or runoff from alkaline soils. Since chloride salts are highly soluble in water, rain will often wash them off.

The amount and character of the deposits vary according to the nature of the soluble materials and the atmospheric conditions. Efflorescence is particularly affected by temperature, humidity and wind. In the summer, even after long rainy periods, moisture evaporates so quickly that comparatively small amounts of efflorescence are brought to the surface. Thus, efflorescence is more common in the winter when a slower rate of evaporation allows migration of salts to the surface. In spring, condensation frozen within the masonry may be released by warm weather allowing for further solubilizing of compounds and their migration to the surface. With the passage of time, efflorescence becomes lighter and less extensive unless an external source of salts or recurrent water migration is present.

In most cases, compounds that cause efflorescence are water soluble and are left on the surface as the water containing them evaporates. Sometimes, however, chemicals in the construction materials react with chemicals in the atmosphere to form the efflorescence. In the case of concrete masonry or mortar, the hydrated cement contains some calcium hydroxide (soluble) as a product of the reaction between cement or lime and water. When this calcium hydroxide is brought to the surface by water it combines with carbon dioxide in the air to form calcium carbonate (slightly soluble), which then appears as a whitish deposit.

Cements used in the production of mortar and concrete masonry units contain small amounts of water soluble compounds of sodium and potassium. Such water soluble alkalis, present as only a few tenths of one percent, can appear as efflorescence when leached out of the masonry by migrating moisture and concentrated at some point on the surface.

In addition to the masonry materials, building trim such as concrete copings, sills and lintels may also contain considerable amounts of soluble compounds. Some admixtures or ground water may also contribute to efflorescence. Most admixtures are proprietary and their compositions are not disclosed. Accordingly, the efflorescence potential of such admixtures should be determined by experience or laboratory tests. Dispersing agents used in pigments may increase the potential for efflorescence.

Sources of Moisture

Water serves as the vehicle by which soluble salts and bases are transported to the surface, where they accumulate as the water evaporates. The primary source of moisture is rain water. Rain water may enter the wall through one or more of the following paths permeable masonry units, partially filled mortar joints, inadequate flashing and sealing details, and cracks or other openings in the wall.

Considerable moisture may also enter a masonry wall as vapor from the interior of a building and accumulate within the wall as it condenses. Excessive accumulation of condensed water vapor may lead to efflorescence.

A third source of moisture that may contribute to the future formation of efflorescence is water that enters the masonry during construction. Improper protection of masonry during and after construction can allow considerable moisture to enter, which can cause efflorescence.

Masonry in contact with soil, such as in basement and retaining walls, may absorb ground water containing soluble salts. Through capillary action, salts present in the soil may rise several feet above the ground, producing an accumulation of salts in the masonry.

CONTROL OF EFFLORESCENCE

Since many factors influence the formation of efflorescence, it is difficult to predict if and when it will appear. However, to reduce the probability of efflorescence occurring in masonry construction, it is necessary to minimize the amount of soluble salts and moisture present in the masonry. Of the two, moisture is the more easily avoided.

Design

The reduction of moisture in concrete masonry will minimize the mechanisms that cause efflorescence. The designer must review each area of the design prior to construction to see if water can enter and where it will flow or accumulate if it does enter.

The selection of wall type—single-wythe, multi-wythe or cavity should be considered from the standpoint of resistance to rain penetration and the exposures to which it may be subjected. Design details that will prevent the entrance of moisture into the masonry assembly are critical. Details that will direct water collection away from wall tops and horizontal surfaces should be considered. If architecturally feasible, wide overhanging roofs help protect walls from rainfall.

Parapets require special attention because of their exposure.

Flashing should be installed in locations where water will tend to accumulate (i.e., parapets, spandrels, lintels, base of wall) within the masonry. The flashing should be installed to direct the water outward through weep holes.

Joints between masonry and door and window openings should be given careful attention during design as well as construction. Backer rods and sealants should be properly selected and installed in the same careful manner as other elements in the structure. TEK 19-02B Design for Dry Single-Wythe Concrete Masonry Walls and TEK 19 04A Flashing Strategies for Concrete Masonry Walls (refs. 1, 2) provide a more complete discussion on the proper use of flashings and details to minimize water entry.

Numerous surface treatments are available for the construction of weathertight concrete masonry walls. Properly applied, coatings can be relied on to give a satisfactory weathertight concrete masonry wall for up to 10 years in most geographic areas. Clear water-repellent surface treatments decrease efflorescence by repelling water from entering the masonry. However, the application of clear coatings to a masonry wall that has the tendency to effloresce, without reducing the mechanisms for the occurrence of that efflorescence, may lead to surface spalling of masonry units or deposits on the interior and/or exterior surface of the surface treatment.

The designer and owner may also want to consider the use of integral water repellents in the masonry. Integral water repellent admixtures have been shown to reduce the tendency to effloresce, since they reduce water migration throughout the wall. For more information on surface treatments and integral water repellents see TEK 19-01 Water Repellents for Concrete Masonry Walls (ref. 3).

Materials

In the selection of masonry materials, all component parts—masonry units, mortar and grout—should be considered for their soluble salt content.

At present there is no standard test for evaluating the efflorescence potential of concrete masonry units or mortar. However, in light of this absence, Standard Test Methods of Sampling and Testing Brick and Structural Clay Tile, ASTM C 67 (ref. 4) which does contain a test method to estimate efflorescence potential, is occasionally specified to evaluate concrete masonry units for efflorescence potential.

All cement should meet applicable ASTM specifications. Lime should be hydrated lime and should meet the requirements of ASTM C 207 (ref. 5). Sand should meet the requirements of ASTM C 144 (ref. 6) and clean mixing water should be used.

If walls of hollow masonry units are to be insulated by filling the cores, the insulating material should be free of harmful salts.

Construction

Materials received at the construction project should be properly stored throughout the construction process. Units should be stored on pallets, or otherwise isolated from the ground, and be adequately covered to prevent water absorption.

Materials removed from stockpiles should be handled such that they remain protected from rain and soil. If colored units are involved, the distribution from the stockpile should be such that the color range of the units is known and units with acceptable color variations are uniformly dispersed throughout the field of the masonry.

During construction, the mixer, mortar box and mortar boards should be kept clean. During cold weather construction, this equipment should not be deiced with salt or antifreeze material. Tools should also be clean and free of rust, salts and other harmful material. For example, workers should not use a shovel for salt and then use it for sand without first thoroughly washing the shovel.

Inadequate hydration of cementitious materials caused by cold temperatures, premature drying or improper use of admixtures should be prevented.

At the end of the work day and after completing one segment of masonry, the top surface of the masonry should be protected to prevent water penetration. Uncovered masonry walls are vulnerable to large quantities of water entering the wall.

Close cooperation between the masonry contractor and designer is necessary to ensure good design and detailing are correctly carried through the construction. Workmanship greatly influences the weathertightness of concrete masonry walls. Concave or vee-shaped mortar joints should be used where the masonry will be subjected to rain or freeze-thaw exposure. Tooling of the joints should be delayed until the mortar is “thumbprint hard”. This partial setting of the mortar provides resistance to the tooling action and forces the mortar tightly against the face shell of the unit to form a good weathertight seal. Joints that do not provide compression of the mortar during the tooling process such as raked, flush, and cut joints are not recommended for exterior applications. They not only do not provide the necessary compressing action against the unit, but by their very nature, leave a ledge for water to accumulate and slowly soak into the masonry.

Head joints are more vulnerable to leakage and poor workmanship as the force of gravity is not working to compress the mortar against the unit to provide a good seal. Head joints must be properly filled to the full thickness of the face shell and compacted by shoving the unit being placed against the previously laid unit. Then of course, the joint must be properly tooled. The use of water to remove surface accumulations, including efflorescence, will cause additional water to enter the wall particularly if it is applied under high pressure. This water may promote further efflorescence.

REMOVAL OF EFFLORESCENCE

Before any effort to remove the efflorescence is undertaken, the reason for the efflorescence should be established. If it is “early age efflorescence,” moist construction materials may be the cause. If “late age efflorescence” is observed, the possibility of water leakage should be investigated. If the efflorescence is near ground level, ground water may be the cause. In any case, the problem should be repaired prior to removing the efflorescence. Generally, if efflorescence is the main concern regarding masonry surface discoloration, the masonry walls should be allowed to cure and then the salts should be removed.

Compared to other stains, the removal of most types of efflorescence is relatively easy. As stated previously, most efflorescing salts are water soluble and many will disappear with normal weathering unless there is some external source of salts.

In general, most efflorescence can be removed by dry brushing followed by flushing with clean water. If brushing is not satisfactory, it may be necessary to use a very light (brush) sandblasting to remove the deposits. Brush sandblasting is sandblasting which is light enough that coarse aggregate is not exposed by the sand blasting (ref. 7). Sand blasting needs to be done with care, as it can alter the appearance of masonry by roughening the surface or exposing aggregate. There also are a variety of commercial cleaners available which may be effective for efflorescence removal. Consult manufacturer’s information for applicability.

As a last resort, a dilute solution of muriatic acid (5 to 10 percent) is sometimes used to clean the wall. For integrally colored masonry, a more dilute solution (2 percent) may be necessary to prevent surface etching that may alter colors and textures. Before an acid treatment is used on any masonry wall, the solution should be tested on a small, inconspicuous portion to be sure there is no adverse effect.

Before applying an acid solution, always wet the wall surface with clean water to prevent the acid from being absorbed deeply into the wall where damage may occur. Application should be to small areas of not more than 4 ft 2 (0.37 m2) at a time, with a delay of about 5 minutes before scouring the salt deposit with a stiff bristle brush. Use a special acid cleaning brush. Do not use a wire brush as the filings of wire left behind could result in further staining as the steel corrodes. After this treatment, the surface should be immediately and thoroughly flushed with clean water to remove all acid. If the surface is to be painted, it should be thoroughly flushed with water and allowed to weather for at least one month.

Since an acid treatment may slightly change the appearance, the entire wall should be treated to avoid uneven discoloration or mottled effects. Windows, doors, or surrounding materials may need to be protected during application.

Calcium carbonate efflorescence is extremely difficult to remove. It appears usually as a flat white deposit and in the worst cases forms a hard white crust. Any effective methods of removal can alter the texture of the block to such an extent that it is necessary to treat the entire wall area and not merely the affected regions. One method of removal reported to be effective is the use of high pressure water jet, sometimes augmented with the addition of fine sand to the water.

REFERENCES

Design for Dry Single-Wythe Concrete Masonry Walls, TEK 19-02B, Concrete Masonry & Hardscapes Association, 2012.
Flashing Strategies for Concrete Masonry Walls, TEK 19-04A, Concrete Masonry & Hardscapes Association, 2003.
Water Repellents for Concrete Masonry Walls, TEK 19-01, Concrete Masonry & Hardscapes Association, 2002.
Standard Test Methods for Sampling and Testing Brick and Structural Clay Tile, ASTM C 67-02c, American Society for Testing Methods, Philadelphia, PA 2002
Standard Specification for Hydrated Lime for Masonry Purposes, ASTM C 207-91(1997). American Society for Testing and Materials, 1997.
Standard Specification for Aggregate for Masonry Mortar, ASTM C 144-02, American Society for Testing Methods, Philadelphia, PA, 2002.
Maintenance of Concrete Masonry Walls, TEK 08-01A, Concrete Masonry & Hardscapes Association, 1998.

Removal of Stains From Concrete Masonry

August 2018

INTRODUCTION

With the continued use and expanding applications of architectural concrete masonry, segmental retaining wall units, and concrete pavers, exposed concrete masonry is becoming common across the country. Although maintenance of a well designed and constructed masonry wall is minimal, inadvertent staining from oil, grease, or other foreign substances can destroy the appearance of an otherwise attractive unpainted masonry structure. This publication provides information on effective methods for removing some of the most common stains.

STAIN PREVENTION

Many stains can be prevented or minimized through proper design, construction, and maintenance procedures. For instance design details that prevent or reduce water intrusion reduce the chance that efflorescence will occur – see Maintenance of Concrete Masonry Walls, TEK 08-01A (ref. 1).

During construction of exposed concrete masonry, minimize mortar and grout smears on the face of the units. Mortar droppings which adhere to the exposed face of the units can be removed with a trowel or chisel after being allowed to harden. Any remaining mortar can then be removed with a stiff fiber brush. Also, the base of the wall should be protected from splashing mud and mortar droppings by spreading plastic sheets 3 to 4 feet on the ground and 2 to 3 feet up the wall. Covering the tops of unfinished walls at the end of the workday prevents rain from entering the wall and thus reduces the chance of efflorescence forming on the wall. Covers should be draped at least two feet down each side of the wall and a method provided to hold them in place. See Cleaning Concrete Masonry, TEK 08-04A (ref. 6) for more information on cleaning concrete masonry during construction and further information on cleaning concrete masonry.

PLANNING AND PRECAUTIONS

The cleaning procedure should be carefully planned. No attempt should be made to remove a stain until it is identified and its removal agent determined. If the staining substance cannot be identified, it is necessary to experiment with different methods on an inconspicuous area. The indiscriminate use of an inappropriate product or the improper application of a product may result in spreading the stain over a larger area or in causing a more unsightly, difficult to remove stain. Removing stains from concrete masonry sometimes can leave the treated area lighter in color than the surrounding area because surface dirt has been removed along with the stain or the surface has become slightly bleached. This is particularly true for buildings that are several years old. This may necessitate treating the entire wall. Materials such as glass, metal, wood or architectural concrete or concrete masonry adjacent to the area to be cleaned should be adequately protected since they may be damaged by contact with some stain removers or by physical cleaning methods.

Many chemicals can be applied to concrete masonry without appreciable injury to the surface, but strong acids or chemicals with a strong acid reaction definitely should be avoided. Even weak acids should be used only as a last resort as it dissolves the cement matrix of the masonry beginning at the surface. This leaves the face more porous so that it absorbs more water and exposes more aggregate thereby changing the color and texture of the masonry.

CLEANING METHODS

The methods of cleaning concrete masonry can generally be divided into three categories water cleaning, abrasive cleaning, and chemical cleaning (ref. 2).

Water Cleaning

Water cleaning includes the use of water soaking, steam cleaning and pressure washing. Cleaning of unpainted walls can usually be accomplished by scrubbing with water and a small amount of detergent. Clay or dirt first should be removed with a dry brush. Steel wire brushes should not be used because they can leave metal particles on the surface of the masonry that later may rust and stain the masonry. Nonmetal brushes such as stiff fiber or nylon are preferred. Soaking with water causes dirt deposits to swell, loosening their grip on the underlying masonry and then allowing them to be flushed away with water. Some efflorescence can be removed when it first appears by dry brushing followed by flushing with water. More extensive efflorescence may require brushing with acid see the section on chemical cleaning or Control and Removal of Efflorescence, TEK 08-03A (ref. 3).

Heated water is useful on greasy surfaces or during cold weather. However, warm water when used with alkaline chemicals, should not exceed 160° F (71° C). There is no significant advantage to using hot water with acid cleaners (ref. 2).

Steam cleaning virtually has been supplanted by improved and innovative pressure washing equipment. However, by supplementing heat to the soaking with water, the action of loosening and softening of dirt particles and grease is improved allowing them to be more easily rinsed away. The steam is normally generated in a flash boiler and directed toward the stain by means of a wand at a pressure of 10 to 80 psi depending on the equipment used. A drawback with steam cleaning is that is rather slow when compared to pressure washing. An advantage of steam cleaning is that it essentially leaves the concrete masonry surface intact.

High-pressure washing equipment can be extremely effective for restorative cleaning of older masonry; however, when improperly applied, it can cause severe damage. If pressure application of chemical cleaning agents is considered, the surfaces to be cleaned must be thoroughly prewetted, cleansing agents must be prediluted, and the application pressures should be kept to a minimum. High pressure washing, however, should not be mistaken as a total replacement for hand labor. The mild agitation created by brush application improves the overall cleaning results while enabling rinsing pressure to be kept to a minimum.

Abrasive Cleaning

The objective in abrasive cleaning is not to dissolve and wash away the stain, but to remove the outer portion of the masonry in which the stain is deposited. Included in this category are grinding wheels, sanding discs, sanding belts, and the more popular grit blasting. Silica sand in recent years has been replaced as the abrasive blasting material by other products such as crushed slag in the concern over health hazards posed by airborne silica dusts. Protective equipment and clothing must be used, including an approved respirator under a hood.

Care must be exercised when using abrasive cleaning techniques since over zealous applications can cause drastic changes to the appearance, durability, and water tightness of the masonry. To minimize this, softer, less damaging abrasives such as crushed cornhusks, walnut shells, glass beads, etc. can be used on more delicate surfaces. This process, sometimes called micro-peening, is slower and more costly and generally is not applicable to large scale cleaning operations.

Most of the dust that accompanies the dry process can be eliminated with wet abrasive cleaning by introducing water into the air-grit stream at the nozzle. However the smaller, harmful particles remain a health hazard so the same protective equipment and clothing are needed as for the dry process. The wet process requires the extra step of rinsing down the cleaned surface after blasting.

Needless to say, previously applied waterproofing agents are removed during the abrasive cleaning process. Therefore, they need to be reapplied after abrasive cleaning.

Chemical Cleaning

The popularity of chemical cleaning techniques has increased substantially in recent years. When used in conjunction with one of the water washing techniques previously described, chemical solvents dissolve staining materials and allow them to be washed away during the final rinsing process.

Many proprietary cleansing agents for removal of stains are available today. They are generally much safer for the user in that the chemicals are premixed so there virtually is no danger of mixing reactive chemicals and also for the masonry in that they are mixed in the proper proportions. Strict adherence to the manufacturer’s directions is still required, however, as improper use can still pose danger to both the user and the masonry. For the most part, products suitable for concrete are suitable for concrete masonry and can be found at most construction specialty and automotive supply centers and at hardware or paint stores.

Tables 1 and 2 provide information covering the removal of many common materials that stain. Table 1 describes the chemicals, detergents, or poultice materials recommended for a particular stain. Table 1 also provides letter keys which indicate steps to be followed in the removal of the stain identified in Table 2.

A poultice is a paste made with a solvent or reagent and a finely powdered, absorbent, inert material used to keep stains from penetrating deeper or spreading. It also tends to pull the stain out of the pores. Enough of the solvent or reagent is added to a small quantity of the inert material to make a smooth paste. The paste is spread in a ¼ in. to ½ in. (6 to 13 mm) thick layer onto the stained area and allowed to dry. The solvent dissolves the staining substance and absorbs it into the poultice and is left as a loose, dried powdery residue that can be scraped or brushed off (ref.4). This process frequently takes several applications to remove the stain.

CHEMICAL SUBSTANCES

The following text provides general information on the chemicals and cleaning agents referenced in Table 1 (ref. 5). As with any chemical, refer to the chemical’s Material Safety Data Sheet and always follow label directions.

Ammonium Chloride (Other names: Amchlor, chloride of ammonia, darammon, salammonite)
Odorless white crystalline substance used in some agricultural processes. Available from chemical and dry-cleaning supply centers and hardware stores.
Hazards: Toxic and corrosive.

Ammonium Citrate (Other names: Citric acid, diammonium salt) White odorless substance in either granular or crystalline form. Found at supermarkets and hardware stores. Hazards: Corrosive and flammable.

Ammonium Hydroxide (Other names: Ammonia solution, ammonia water, household ammonia) A colorless liquid with a strong irritating odor. Found at most supermarkets and hardware stores. Hazards: Toxic.

Ammonium Sulfamate (Other names: Amicide, ammonium amidosulphate) A white crystalline substance commonly used as a weed killer. Found at chemical and garden supply centers. Hazards: None.

Benzene (Other names: Benzol, benzole, coal naptha) An excellent solvent and colorless liquid with characteristic odor and burning taste. Found at automotive, chemical and dry cleaning supply centers and hardware and paint stores. Hazards: Violently flammable and carcinogenic

Calcium Hypochlorite (Other names: B-K Powder, losantin, pool chlorine) White in powder, granule, or pellet form used to kill algae, fungus, and bacteria. Found in pool chemical and garden supply centers. Hazards: Corrosive to flesh and flammable when in contact with organic solvents.

Carbon Tetrachloride (Other names: Perchloromethane, tetrachloromethane) A nonflammable, clear, poisonous liquid used in fire extinguishers and as a solvent. Available at chemical, dry cleaning, and pharmaceutical supply centers, and paint stores. Hazards: Toxic.

Glycerine (Other names: Glycerol, glycyl alcohol) An odorless, colorless, syrupy liquid prepared by the hydrolysis of fats and oils. Found at chemical, pharmaceutical, photographic, and printer supply centers. Hazards: Flammable.

Denatured Alcohol (Other names: Methylated Spirit) Found at pharmaceutical and printer supply centers and hardware stores. Hazards: Toxic and flammable.

Hydrochloric Acid (Other names: Muriatic acid) A strong, highly corrosive acid commonly used for cleaning metals and balancing the pH of swimming pools. It can be found at swimming pool supply centers, chemical supply centers and hardware stores. Hazards: Toxic, very corrosive to flesh and concrete materials. Reacts vigorously with ammonia and detergents containing ammonia. Use extreme caution when handling and applying. Never use full strength. Dilute by adding acid to water, never water to acid. Rinse thoroughly within 10 minutes after applying.

Hydrogen Peroxide (Peroxide of hydrogen) A colorless, syrupy liquid used as a bleaching and disinfectant in low concentrations and as a rocket fuel in higher concentrations. Available at chemical supply centers, drug stores, supermarkets, and hardware stores. Hazards: None in the normal 3% solution. Toxic, corrosive to flesh and flammable in higher concentrations.

Sodium Citrate (Other names: Citrate of soda, trisodium citrate) White odorless substance in crystalline, granular, or powder form. Commonly used as a neutralizing buffer in chemical research. Available from chemical supply centers and drug stores. Hazards: None.

Sodium Hydrosulfite (Other names: Hydrolin) White powder with little odor. Commonly used in industrial cleaners. Found at chemical supply centers. Hazards: Very toxic when in contact with moisture.

Sodium Hypochlorite (Other names: Clorox, hypochlorous acid, household bleach) Faint yellow to clear liquid with chlorine smell. Available at supermarkets. Hazards: Corrosive to flesh.

Sodium Perborate (Other names: Perboric acid, perborax, sodium salt) White, odorless, crystalline powder commonly found in “allinone” laundry detergents and some dishwashing powders. Available at chemical and pharmaceutical supply centers and supermarkets. Hazards: Toxic and flammable when in contact with organic solvents.

Trichloroethylene (Other names: TCE, ethynyl trichloride) Colorless liquid with chloroform smell found in common cleaning solvents. Available at automotive, chemical, dry cleaning, paint, photographic, and printer’s supply centers. Hazards: Highly toxic and can react with strong alkalies in fresh mortar or concrete to form dangerous gases.

Trisodium Phosphate (Other names: Sodium orthophosphate, TSP, phosphate of soda) A crystalline, white, odorless compound found in household cleaning detergents such as “Spic and Span”. Available at supermarkets and hardware stores. Hazards: Corrosive to flesh

MATERIALS FOR POULTICES

The main properties desired in the powdered materials used to make poultices are: 1) grains sufficiently fine so the paste will hold plenty of liquid; 2) enough range in particle size so they will make a smooth, readily moldable paste; and 3) chemical inertness to the chemicals with which the powdered material is used. The last precludes using portland cement in combination with water, although it can be used with organic liquids. For the same reason, if acids are to be used, the paste must not be made with whiting (calcium carbonate), ground limestone, hydrated lime, or portland cement. Otherwise, the finely divided materials are more or less interchangeable.

Diatomaceous Earth (Other name: Diatomite, filter media, fuller’s earth) Available at swimming pool supply centers.

Lime (Other names: Calcium hydroxide, caustic lime, mason’s lime, quicklime) Available at building material supply centers and nurseries.

Portland Cement (Other names: Cement) Found at building material supply centers and ready mixed concrete plants.

Talc (Other names: Talcum powder) A very soft mineral that is a basic silicate of magnesium, has a soapy feel, usually white in color, and is used especially in making talcum powder. Available at supermarkets and drug stores.

Whiting (Other names: Calcium carbonate, baking powder) Found in nature as calcite and aragonite and in plant ashes, bones and shells. Available at supermarkets and nurseries.

REFERENCES

Maintenance of Concrete Masonry Walls, TEK 08-01A, Concrete Masonry & Hardscapes Association, 2004
Grimm, Clayford T., Cleaning Masonry A Review of the Literature, Construction Research Center, University of Texas at Arlington, November 1988.
Control and Removal of Efflorescence, TEK 08-03A. Concrete Masonry & Hardscapes Association, 2003.
Removing Stains and Cleaning Concrete Surfaces, Portland Cement Association, 1988.
Removing Stains from Concrete, Concrete Construction Publications, Inc., May 1987.
Cleaning Concrete Masonry, TEK 08-04A, Concrete Masonry & Hardscapes Association, 2005.