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Acid Stain Instructions

EnduraColor Reactive Concrete Stain

EnduraColor Reactive Concrete Stain can be applied to new or old, plain or colored concrete surfaces. They are available in 12 basic colors. Acid Stains react with the cement in the concrete to permanently change the color. Siliceous aggregates, such as gravel and sand do not react with the stain. Surfaces that contain higher cement content will produce more intense colors.

Since every concrete slab matrix composition is different, the outcome will vary from one surface to another. Sometimes testing a small inconspicuous area will help determine what the outcome will be. Please note that the color will not be final until the sealer coat has been applied. With wood stain you can still see the grain of the wood through the stain, acid stain is very similar to this as you can see any blemishes or finish marks through it.

Factors that can affect the outcome include:

  • Cement properties and amount used, admixtures and type of aggregate used
  • Concrete finishing methods, concrete age, and moisture content
  • Porosity and Texture of the surface
  • Weather conditions when the stain is applied
  • Efflorescence

Equipment Needed

EnduraColor Reactive Concrete Stain finishes do not require allot of expensive equipment for application. The average applicator uses a standard all poly (plastic) garden sprayer, a brush or a combination of both.  A black foam squeegee, shop vac, mop & ringer are used for the cleaning and neutralizing of interior projects. Any equipment used to apply reactive stains can be easily cleaned with fresh water and reused for other applications. Standard nylon paint brushes are used to for "cutting in" tight areas for the reactive stain and sealer application.

Applicators should wear the proper safety equipment including latex gloves, goggles, boots, and face masks to filter acid vapors.

Surface Preparation

Proper surface preparation is considered to be the most important step of any concrete stain or coating application. It is a large factor for the immediate and long-term performance of all decorative concrete projects. Improper surface preparation could turn what seems to be a simple process into a lengthy and difficult repair.

First sprinkle a little water on the surface in several locations to see if the concrete absorbs water. If it does not absorb into the concrete within 10-15 seconds, you may have 1 of 2 surface issues; 1)  a concrete sealer coating or "cure & seal" may be on your concrete surface.  These sealers were applied to help strengthen the concrete during the initial construction but will need to be removed for the staining process.  You can either lightly sand or grind the surface or use several types of strippers to remove these thin sealers.  2)  "Over power troweling" of the concrete when it was poured can also inhibit the concrete surface to absorb water & reactive with concrete stains. It is extremely important to "open" these very hard or dense concrete surfaces, such as garage floors, large open concrete surfaces, etc.  Some of these types of floors can look like they have a slight sheen or a dark gray or sometimes even charcoal black hues. If sanding or light grinding is not an option, our EnduraPrep Concrete Surface Conditioner is an alternative to mechanical surface preparation.  It was designed to open, non previously sealed, dense concrete surfaces that can be applied with the same garden sprayer and in the same manner as the reactive stains.  A properly conditioned concrete surface should feel about like 120-grit sandpaper and be thoroughly rinsed before applying the EnduraColor Reactive Concrete Stain DO NOT USE MURIATIC ACID on the surface as it will deprive the concrete of the minerals necessary to react with the concrete stain.

The final preparation step involves careful and a meticulously washed surface with plenty of fresh water. It is ALWAYS advisable to use a slow speed floor scrubber with a medium bristle brush attachment to properly remove any of the contaminates on smooth concrete surfaces.  Your surface must be clean and free of any grease and oil, paint drops, taping compounds, caulk, plumbers flux or other types of surface contaminants. Anything remaining on the surface will affect the final outcome of the surface. EnduraPrep Cleaner& Degreaser is great for cleaning of these types of surface contaminants.

If a slab must be patched, use acrylic-modified, fine grout compounds.  These patches will always stain differently in the final outcome and the owner should be made aware of this.  You can also "faux" finish these areas to help make these patches look more like the overall color.

Decorative saw cuts can also enhance the appearance of stained surfaces. Timing of these operations, though, depends on the desired effect.  The cut lines and patterns will penetrate through the stain to the concrete to original concrete and will always look lighter. 

Stain Application

The industry standard is that a new slab must cure for 28 days before work is started.  Depending on several variables such as the type of concrete, temperature, elevated slab, etc, reactive stains can be applied over concrete in as little as 14 to 21 days.

When applying reactive acid stains, keep the following things in mind:

  • Moisture affects the acid stain reaction. To achieve color consistency, make sure the moisture content of the concrete is roughly the same for every placement colored.
  • Staining, sealing, and covering finished work before other construction trades will save on preparation and cleanup.  It will also help achieve a better looking installation and makes damage repair during the rest of construction easier to handle.  DO NOT tape construction paper or cardboard to the stained floor as it will adhere to the coating and delaminate when removed.

There are many ways to apply stain, with each method, providing a different final appearance. However, there are some general guidelines:

Use a standard, all poly (plastic) garden sprayer with a tip that sprays a circular or round pattern.  During application, if a floor scrubber was not used earlier over smooth surfaces, it is advisable to scrub the stain in with a 7" deck brush. An additional spray pass just behind the scrubbing will help remove any brush marks. This method ensures good penetration and minimal markings from the brush.

When applying stains in tight areas, along walls or around posts, a standard nylon paint brush is standard equipment.  Whatever stain application method is used, be sure to carefully mask surrounding areas to avoid accidental staining. Reactive acid stains can, in some cases be difficult to remove.

EnduraColor Reactive Stain Extender can be used to dilute the stain achieving lighter stain color.

With increased interest in acid stain finishes, more subtle effects have become popular. Installers frequently dilute stains with stain extender to produce less intense effects. For example, some contractors often apply the stain with an 80% stain dilution (20% stain extender by volume). In this manner, the contractor can gradually build up color to meet owner expectations. Second and third colors can also be added in the same fashion to create color overlays.

Sometimes applying a commercial grade concrete overlay or micro topping prior to staining is the best solution for concrete surfaces that show damage, spalling surface or have been abused during construction. Commercial overlay materials can be integrally colored, textured, and stained to provide a new range of decorative possibilities. Many high quality overlays may have good flexural strength and wear resistance. As with everything involving stains, however, it’s wise to create a sample to ensure compatibility of the overlay cement with the stain and to get owner approval for the result.


When most of the chemical reaction is complete, a layer of colored residue with a lower acidic pH may be present on the surface. This layer must be thoroughly neutralized with EnduraPrep Neutralizer and applied liberally so the sealer will bond properly when applied to the surface. Use a white rag after several cleanings to check for residue. Also, it is a good to apply 3-5 gallons of fresh tap water for every gallon of reactive acid stain during and after neutralizing to ensure the surface is ready for the next step of applying the clear sealer.

Applying Sealer

Whether applying EnduraSeal 100%  Solvent-based acrylic or EnduraSeal WB water-based acrylic clear sealerit is best to allow 24-48 hours for the stained concrete slab to dry so moisture has enough time to evaporate before application.   Two thin coats give the best uniform results.  The best maintenance procedure for interior smooth concrete is applying Endura Seal Floor Finish.  This adds a tough, sacrificial coating to your existing surface and increases durability and gloss.  Coverage may be up to 1000 sq ft or more per gallon over previously smooth sealed concrete surfaces.