Because of the very nature of the material and the limitless variety of the exposure conditions to which it is subjected, one of the most common esthetic faults to be found with concrete is its affinity for various agencies which cause staining. Fortunately, it is not necessary to be either a chemist or a magician to remove most stains relatively easily. Well defined methods are now available to remove effectively most stains on concrete which results from exposure to materials commonly found on construction sites or used in buildings. The green stain which is created when water flows over exposed copper or bronze is a common sight on masonry structures. The discoloration can be removed as follows: mix thoroughly, in the dry state, 1 part by weight of dry powdered ammonium chloride and 4 parts by weight of a suitable filler such a diatomaceous earth. Form a smooth paste by adding ammonia water. Apply a layer of paste one-eighth to one-fourth inch thick over the stained area; do not remove until dry. Three such applications are usually sufficient to remove even the most severe stains. Rust stains on concrete are common; they usually result from the weathering of unpainted or unprotected structural steel. The materials needed for removal are: one ounce of sodium citrate dissolved in 6 ounces of water, crystals of sodium hydrosulphite, paste of whiting, and water. Apply the solution by brush at 5 to 10 minute intervals until the area is thoroughly soaked. Next, if the stain is on a horizontal surface, sprinkle it with the crystals of sodium hydrosulphite and then cover it with the paste. For a vertical surface take the paste on a trowel, sprinkle it with the crystals and plaster over the area, keeping the crystals in direct contact with the stain. A single application of this treatment is usually adequate. With any oil spillage it is best to take immediate steps to remove as much of the oil as possible by sucking it up into an absorbent material such as hydrated lime. The procedure then is as follows: mix thoroughly 1 part of trisodium phosphate, 1 part of sodium perborate, and 3 parts of powdered talc. Add liquid green soap in to form a paste. Cover the stain with a one-eighth of an inch layer of the paste, remove the paste when it is thoroughly dry, and scrub the surface with clean water. Application should be repeated as necessary. The article goes on and discusses the remove of petroleum oils, grease, asphalt, wood tar, smoke, creosote, paint and inks.