How to Acid Stain - Surface Preparation

Surface preparation is the most important step in the acid staining process.

How Concrete Acid Stain Works

Concrete Acid Stain is a water-based liquid bearing minerals and acid. The acid stain penetrates the pores of the concrete forcing a chemical reaction between the muriatic acid and the available lime in the surface.

Once acid stained, the color of the concrete is permanently altered. When sealed with an appropriate concrete sealer and for indoor applications, sealed and waxed, acid stain produces the unique, variegated finish associated with this process.

Surface Preparation

Surface preparation is the most important step in the acid staining process. Prior to staining, a slab must meet the following criteria:

  • The concrete must be free of debris, dirt and oils, paint, dry wall mud, adhesive, sealers, stains of any kind or similar materials. Acid stain cannot react properly with the concrete if these conditions are present.
  • The slab should not have been treated with a waterproofing agent, cleaned with muriatic acid or a heavy tri-sodium phosphate (TSP) solution. The acid stain reaction cannot occur on surfaces treated with these products.
  • For older, excessively power-washed, or mechanically-profiled concrete, the surface must be completely intact with no exposed aggregate or sand particles. Concrete acid stain does not stain rocks, sand or aggregate. Exposed aggregate or otherwise depleted concrete may cause the acid stain to take irregularly, react weakly or produce a color inconsistent with the acid stain color chart.
  • For slick machine-troweled surfaces, apply DCI Hard-Troweled Floor Prep according to the instructions to insure a complete acid stain reaction across the floor. Test by pouring water on the surface. If the water beads up and sits on the surface for more than a few seconds, the hard-troweled floor prep will be needed.
  • Newly poured concrete should include less than 10% fly ash to insure a good chemical reaction with the acid stain. Concrete poured with excessive water in the mix can create a thin, unstable layer of concrete on the slab surface. To test for instability, press the tip of nail into the concrete. If breaking or damage of any kind occurs, the slab must be profiled with a sander or buffer using a 60-80 grit sanding disc before staining.


NOTHING takes the place of pre-application testing, particularly if you do not know the history of your slab. Always prepare a test area on the slab intended for staining prior to beginning a project. Direct Colors is not responsible for application problems resulting from a failure to start projects with a sample test.

Often, concrete surfaces will have dry wall mud, paint, wood stains, tile adhesives, carpet adhesives, grease, pet stains, etc. on the concrete. Concrete Acid Stain is not an over coat, but is an opaque, penetrating color that permanently changes the appearance of the concrete. Areas where debris remains on the surface will likely not accept the stain leaving color imperfections on the floor, particularly mastic, dry wall mud and paint. Use Bean-E-Doo, for the removal of adhesives. Apply Soy Gel Professional Paint Stripper to remove epoxy, sealers, varnish or paint. For more information on these and other concrete cleaning products, visit Xylene can also be used to remove solvent-based sealers and clean up sprayers or tools. Soap and hot water can be used to remove water-based sealer from applicators immediately after application but Soy Gel Professional Paint Stripper or a similar product is required to strip water-based sealers from concrete. Cleaning floors that have been heavily soiled or have been previously tiled or carpeted to a stainable level is a considerable amount of work, but not impossible. If you desire a more even finish, consider overlay resurfacing especially on slabs with exposed aggregate or surfaces so soiled that cleaning would prove too difficult.

For best acid stain results on indoor slabs, sand the floor with a 150-200 grit pad applied with a floor buffer to properly prepare the surface for staining. Sanding will remove most if not all debris from the surface and correctly profile the concrete for staining.

The vast majority of slabs only require minimum cleaning using an organic degreaser (such as DCI Orange, Simple Green, etc.) diluted at a medium concentration with water. Scrub the surface with a soft nylon bristle brush or power wash on a low setting to prepare most floors for staining. Thoroughly rinse the surface with clear water to remove any remaining cleanser and leave the floor to dry. For interior projects, use a shop vacuum, mop and/or squeegee to contain the water and aid in drying.

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