Removing Wood Stains from Concrete Northampton MA

Source: THE CONCRETE PRODUCER/CONCRETE JOURNAL MAGAZINE
Publication date: November 1, 1997

After one of our customer-contractors poured an integrally colored patio at a new residential home, the homeowner had the carpenters add a railing to the adjacent redwood deck. Afterward, wood debris covered a portion of the patio. During the final walk-through at loan closing, the homeowner noticed a red stain on the tan-colored concrete. How can the contractor remove the stain to satisfy the owner without replacing the concrete?

The stain in this example was caused by wood extracts. These natural oils permeated concrete surface voids, leaving the brown or red stains. The best way to attack the stain is with early treatment that draws the stain up from the concrete surface with a poultice. A poultice is usually made by mixing some essentially inert fine powder, such as ground limestone, hydrated lime, portland cement or fuller's earth, with the solvent or solution. (Shredded pieces of highly absorbent paper would also work.) The selection of the cleaning liquid is based upon the cause of the stain. The two parts are blended to make a smooth paste that is troweled over the stain. The liquid portion of the poultice migrates into the concrete, where it dissolves some staining material. Then the liquid gradually retreats upward from the concrete into the poultice, from which it evaporates, leaving its burden of dissolved staining material in the poultice's inert powder.

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