Masonry Magazine March 1971 Page. 23
Smoke Stains
Smoke is another difficult stain to remove. A thorough scrubbing with scouring powder (particularly one containing bleach) and a stiff bristle brush works surprisingly well. Some of the alkali detergents and commercial emulsifying agents, such as Nos. 10 and 11, Table 1, brushed or sprayed on and given sufficient time to work, also do a good job. These have the added advantage that they can be used in steam cleaners. For the more stubborn stains, a poultice using trichloroethylene will pull the stain from the pores. Precaution should be taken to ventilate a closed space in which trichloroethylene is used, as the fumes are harmful.
Oil and Tar Stains
Oil and tar stains are also effectively removed by the commercial emulsifying agents, Nos. 10, 11 and 12, Table 1. For heavy tar stains they can first be mixed with kerosene to remove the tar and then with water to remove the kerosene. After application, they can be hosed off of the wall. When used in a steam cleaning apparatus, Nos. 10 and 11 have been known to remove tar without the use of kerosene.
Where the area to be cleaned is small, or in a place where a mess cannot be tolerated, a poultice using benzene, naphtha, or trichloroethylene is most effective in removing oil stains.
Dirt
Dirt is sometimes difficult to remove, particularly from a textured brick. Scouring powder or Nos. 10 and 11, Table 1, and a stiff bristle brush are effective if the texture is not too rough. Scrubbing with the oxalic acid-ammonium bifluoride solution recommended for iron stains has proven effective on some moderately rough textures. For very rough textures, high pressure steam cleaning appears to be the most effective method.
Straw and Paper Stains
Straw and paper stains sometime result from the materials used to pack brick for shipment becoming wet. Not all packing materials will stain brick, but those that do may produce a very stubborn stain. This stain can be removed by applying household bleach and allowing it to dry. However, several applications may be required before the stains disappear. The solution of oxalic acid-ammonium bifluoride recommended for iron stain cleans the stain much more rapidly.
Plant Growth
Occasionally an exterior masonry surface which is not exposed to sunlight and remains in a constantly damp condition will exhibit signs of plant growth, such as moss. Application of ammonium sulfamate (marketed under the manufacturer's brand name and available in gardening supply stores) according to directions furnished with the compound has been used successfully in the removal of such growths.
Stains of Unknown Origin
Stains of unknown origin can be a real challenge at times. Appearance may be the first real clue. Rust-colored stains may actually be rust. Such stains are quite common and have been known to come from mortar ingredients, welding splatter on the back of the brick or something being laid on the pile of brick before they were laid in the wall.
Green stains may be grass, moss or vanadium efflorescence. Brown stains may also be vanadium efflorescence, or possibly manganese staining. Black-stains can be almost anything.
One test, useful in narrowing down the list of possible causes of a stain, involves a substance which ordinarily should not be put on a wall. When concentrated sulfuric acid comes into contact with an organic material, the organic material turns 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
In the paper, "Exterior Building Cleaning," by Rockwell Newman, President of the Rockwell Newman Company, Orange, New Jersey, which was published in the May-June, 1957, issue of Catholic Building and Maintenance, Mr. Newman lists five methods of cleaning exterior masonry walls "in the order of their popularity". They are: high-pressure steam, sandblasting, hand washing, high-pressure cold water blast, and chemical and steam. The following descriptions of various cleaning methods are summarized from his paper.
High-Pressure Steam
Probably more buildings are cleaned by steam than in any other way, because this method lends itself more readily and more satisfactorily to the various types of masonry than any other. Buildings erected with a smooth, hard type of unit or a material with a glazed or vitreous surface should always be cleaned by the steam method. The group would include terra cotta, polished granite or marble, smooth vitreous brick, tile or any unit which might be pocked or etched by sandblasting. Naturally the more impervious a masonry unit, the easier it should clean, and this is generally the case.
In most cases buildings can be cleaned satisfactorily with high-pressure steam only; but where stains have developed, it is sometimes necessary to use a solution of detergent.
Sandblasting
The most commonly used method of sandblast is the dry one, which is simply a combination of sand from a tank forced through a hose