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Removing Concrete Stains

The removal of surface stains can be a simple process or a complex one depending on the nature of the stain. Except for the detraction from the appearance of the surface, many stains are harmless to the concrete and will remain so. There are a few (such as acid stains, for example) that, if left unremoved, will create concrete deterioration. Stains may occur in concrete in the plastic state, such as absorption of form oils, or they may be created by spillage of chemicals or other staining agents months or years after the concrete has hardened. This is when you call Concrete Salt Lake City


Some of the problems are concrete discoloration rather than stains. One area of the concrete may differ from the rest, possibly because of excess water on the subgrade at that spot. The concrete placed above that water would then appear lighter in color. There is the possibility that one load of concrete was a different color from another because a different brand of cement was used. A change in the source of the fine aggregate in the mix may cause a color variation.

Concrete containing calcium chloride will usually dry darker than concrete without this often-used accelerator. A drastic change in slump between loads will vary color. Over Troweling or coating dry cement on the concrete to absorb bleed water will produce burn marks or discoloration. Determination of the cause is necessary before prescribing a cure. Moreover, it is often best to do nothing if the concrete is less than a few months old. When some discolorations are exposed to the sun and weathering over a period of time, the problem area may blend in nicely with the rest of the surface.


A first, generally reliable treatment for discolorations is the application of phosphoric acid, which can be purchased at any local chemical supply house. An acceptable solution for discolored concrete is 1 pt of the acid diluted with 2 gal of water. Mix well and brush over the entire surface. It may bleach the concrete to a whitish color, but the concrete will gradually return to normal over a period of time. If the variation in color is slight, one might try a similar solution of laundry bleach, which is sometimes effective.


Concrete stains are more troublesome than discolorations. The cause of the stain must be determined before successful treatment can be undertaken. Coffee stains, tar, paint, grease, ink, and the many other types of stains all require different methods of removal. Some stains may require trial and error before a cure is obtained. Stains can be removed not only by chemical treatment but also by the mechanical methods of grinding, sandblasting or water blasting, scarifying, or steam-cleaning. Regardless of the method selected, it is necessary to protect nearby objects susceptible to damage from the treatment-wood, siding, glass, metal, machinery, heaters, and air conditioning units. It should also be kept in mind that hot-air heaters and air conditioners can bring dust and chemical odors to other parts of the building during the stain-removing process.

Some stains, such as chewing gum or tar, for example, generally remain on the surface with little or no penetration into the concrete itself. Liquid stains do penetrate into the concrete, with their depth of penetration depending largely on the porosity of the concrete and the type of finish the concrete had initially received. A hard troweled concrete finish will normally not absorb stains as will a wood-floated or broom finish. This is when you should call Concrete Salt Lake City.


Most nonacid chemical treatments, when carefully applied, will not injure the concrete. If acid chemicals are used, the surface to be treated should first be water-saturated to dilute the acid absorbed by the concrete. It is best to experiment on a small test patch to determine the success of any chemical treatment before attempting large areas. Applications of this kind should be left on the test patch for short periods only to determine effectiveness. Two light applications are often more successful and less harmful to the concrete than one heavy dose.

The manufacturer’s instructions for use of any chemical should, of course, be carefully followed. When such chemicals are used indoors, proper ventilation is necessary. Avoid any contact of the chemical on the skin, wear goggles, and be careful not to inhale the fumes. A safer option is to hire a a professional Salt Lake City Concrete Contractor.


Many concrete stains can be removed without mechanical or chemical treatment. A poultice can be applied to the non penetrating stains, such as those from caulking compounds and chewing gum, with little effort and good results. Ice or a poultice (i.e., a mixture of flour and denatured alcohol) can be applied to this type of substance to harden it and make it brittle for easier removal. After this treatment the spot should be washed with hot water and a scouring compound, applied with a stiff bristle brush to remove any remaining residue, Finally the spot should be rinsed well with water after the treatment has been completed. A poultice should be applied as a smooth, non flowing paste and troweled over the problem area in a thickness of 4 in. or slightly more. The stain-removing product used in the paste dissolves the staining substance, which is then absorbed into the poultice. After the poultice has dried, it is easily removed. The poultice method has the advantage of preventing the stain from spreading during treatment.


Epoxy stains are difficult to remove by chemical treatment and may best be eliminated by sandblasting. In the case of grease or oil stains, sandblasting should not be considered, as it may well drive these highly penetrating materials deeper into a porous concrete.

If the cause of a stain is difficult to determine, removal might first be attempted by brushing the area with a strong detergent or scouring powder. A bleach, such as Clorox, may well be worth testing on the stain. In any event, scrape off as much of the stain as possible before any application.


Rust stains, unless deeply embedded, may be treated by mopping the area with a solution of I lb of oxalic acid per 1 gal of water. Wet paint stains will only spread further if they are wiped up. Instead, the paint should be absorbed with paper towels and the residue scrubbed with scouring powder and water. Old, dry paint stains should be scraped off as much as possible, and a poultice, saturated with a commercial paint remover, should be applied.


Asphalts, tars, and pitches have a good adhesion to concrete and are difficult to remove. Before applying any treatment, scrape off any excess bitumen and scrub the surface with scouring powder and water. CAUTION: On concrete surfaces, do not use steel brushes, since particles of the metal may break off and later create rust stains. Do not use solvents, since they will cause the stain to penetrate deeper into the surface. One method, sometimes successfully used in removing such materials, is to apply a bandage saturated with a solution of equal parts of dimethyl sulfoxide and water. Let stand for 1 hour, then scrub the treated area with a stiff brush. (A bandage is a few layers of white cloth)

  • MOSS

Moss occurs frequently on concrete surfaces that are in a constantly damp and shaded location. = Ammonium sulfamate, available from most garden supply stores, has been used successfully in removing such growths. Should a powdery deposit be left on the surface, it can be removed by washing with water.


Lubricating oil and petroleum oil readily penetrate into the concrete surface. If the spillage is noted, it should be soaked up immediately with paper towels or absorbent cloth. Repeat, soak, don’t wipe, as wiping spreads the stain. Cover the spot with a dry powder, such as flour, dry cement, or similar absorbent material, and leave it for a day, Repeat the application as frequently as necessary.


Backyard patios frequently used for eating and entertaining are subjected to many different types of stains. As one treatment may not cure them all, it may be easier to cover the entire area with an acrylic or latex emulsion compound. They are readily available, reasonably inexpensive, easily applied, and durable. A thin coating is sufficient to cover most stains; or one may consider covering the patio, or concrete porch, with outdoor carpeting. Call a concrete contractor if have no experience in dealing with concrete stains.

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