How to Acid Stain Gypcrete or any Gypsum Based Underlayment

These days, coloring concrete surfaces, both old and new, with acid stains (also called reactive stains or chemical stains) is very popular due to its unique appearance and cost effectiveness. Acid staining is a process in which an aqueous solution of metal oxides and inorganic acid is sprayed onto an existing concrete surface. The acidic metal oxide solution reacts with the lime (calcium hydroxide) present in the concrete and produces insoluble colored compounds that become a permanent part of the concrete. Therefore, one of the basic conditions in which the coloring of concrete with acid dyes will work is the presence of lime in the concrete. Often quiet people who have just bought a house or condo remove the carpet or vinyl tiles and find something underneath that they think is concrete. When they spray acid stain or reactive stain and expect to be disappointed that they see no change in the color of their concrete surface. This is because the substrate that looks like concrete is in fact plaster based ‘Gypcrete’. Builders often use this on upper floors to level sub-floor areas and provide a good base for other types of floor coverings. Unfortunately, staining Gypcrete does not produce any desirable results as it does not contain lime; Furthermore, it is too soft and wears out easily. Therefore ‘Gypcrete’ cannot be used as a wear layer.

Since Gypcrete surfaces cannot be used as a wear layer and acid stains do not work on them, it is common practice to apply a 1/16-inch polymer-modified concrete resurfacing material (also called microfinishing or Thin layer). Please find below the steps required to resurface Gypcrete and acid stain with a final microcoat or thin coat:

has. Sweep the Gypcrete surface and dry vacuum the surface thoroughly. Rake the joints where the drywall meets the floor. Clean up adjoining areas, even those not resurfaced, with microtopping.

b. Install masking paper (plastic) at least 48″ high on surrounding walls. Spray a light mist of water only to dampen the surface (DO NOT FLOOD!)

vs Using a new rayon mop, apply first coat of acrylic primer (Cp1000) after diluting it 1:1 with water. After waiting at least 60 minutes, apply a second coat of diluted acrylic primer and allow it to cure overnight (or 10 hours minimum) before proceeding to the next step.

d. Apply another coat of acrylic primer, this time undiluted, and allow it to dry for 30-60 minutes. The third coat of primer can be applied with a garden sprayer (ie available at Home Depot or Lowes).

me. Apply a thin coat (1/16″) of polymer modified microsurface or overlay using a magic trowel. Follow link for specific instructions on applying Sgraffino polymer modified microsurface. Allow microsurface to cure for at least 24 hours In wet and cold conditions (basements), wait at least 48 hours before proceeding to the next step.

F. Apply acid stain on the completely dry microtopping. Follow the link for specific instructions on applying an acid stain, Patinaetch. Allow the acid-stained surface to dry for at least 24 hours before proceeding to the next step.

gram. Microtopping should be protected with a good quality sealer. Apply a coat of water-based epoxy sealer, Perdüre E32, followed by another coat of water-based polyurethane, Perdüre U46. Allow at least 6 hours between the application of the epoxy primer and the top coat of polyurethane. The sealed surface will be ready to use after 24 hours. Of course, it takes at least 3 days for complete healing.

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