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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 10 basic colors. Acid Stains react with the cement in the concrete to permanently change the color. Siliceous aggregates, such as gravel, do not react with the stain. Surfaces that contain higher cement content will produce more intense colors.

Since every concrete slab is different, the outcome will vary from one surface to another. We always recommend testing a small inconspicuous area to 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 don’t require much equipment for application. The average applicator uses a garden sprayer, a brush or a combination of both. Any equipment that comes in contact with the staining liquid, such as sprayers, must be resistant to acid. Brushes used to apply or spread the stain should have acid-resistant, uncolored bristles.

Workers should wear the proper safety equipment including acid-proof gloves, goggles, boots, and face masks to filter acid vapors. A good quality wet vac is highly recommended for cleanup. Steel golf spikes are also recommended because shoe marks will show in the finished stain (Do Not walk on the stain when wet if possible).

Surface Preparation

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

First throw a little water on the surface in several locations to see if the concrete absorbs water. If it isn’t absorbed by the concrete, you may have a concrete sealer coating on your surface. If so, you will need to strip the surface with EnduraPrep Coatings Stripper. This stripper is also great for removal of other coatings like paint or acrylic stains and colorants. If there is not a sealer coating on the surface, yet it won’t absorb water, then there probably isn’t much porosity to your surface. This can be caused by over troweling of the concrete when it was poured. It is extremely important to condition "hard-troweled" or very dense concrete surfaces, such as garage floors, in order to open up the surface and allow a coating to penetrate and bond to the surface. Conditioning of the surface is frequently the key to a successful project. If there is not a sealer coating present, yet the surface still will not accept water, it will definitely need to be conditioned. Sometimes, very dense surfaces will need to be conditioned twice. When the surface is properly conditioned, it should feel like 120-gritsandpaper. If you are going to use 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. A properly conditioned surface can easily be achieved using EnduraPrep Concrete Surface Conditioner, a safe alternative to typical acid etching.

The final preparation step involves carefully washing the surface with water and Cleaner/Degreaser. Your surface must be clean and free of any grease and oil, paint drops, taping compounds, caulk, or other surface contaminants. Anything remaining on the surface will affect the final outcome of the surface. EnduraPrep Cleaner& Degreaser is great for cleaning all surface contaminants.

If a slab must be patched, use acrylic-modified,low-shrinkage materials that will accept stain. These patches will always show in the final outcome and the owner should be made aware of this.

Decorative cuts and sandblasted patterns achieved with stencils can enhance the appearance of stained surfaces. Timing of these operations, though, depends on the desired effect. When you want the overall stain finish to be as evenly colored as possible, cut lines and patterns after staining is complete. Stains penetrate differently around indentations. If there is to be a color change at a pattern line, cut the line first to form a barrier to stain movement. If sawed joints are to be grouted, complete the staining and sealing before grouting to help prevent grout accumulation on the unprotected stain.

Pattern lines are generally laid out with pencil or chalk. Mark only where you cut, and don’t use chalk colors that are difficult to remove, or adhere lines to the concrete surface using clear fixative sprays. Many tools are available for cutting pattern lines in concrete. Most installers use grinders or hand-held saws with tables that ride against guides. A 1-1/2 inch extruded aluminum “L” angel, available in most hardware stores, makes a good saw guide. Dry-cutting diamond blades that do minimum damage to the edge of the cut are a good choice. Dust-collection devices that attach to grinders and saws are very good to use.

If you cut patterns before staining, cut them just before cleaning the surface in preparation for the stain. Sawing dust contains free lime that can adhere to the surface, causing distortion. If you cut after staining, do it after the first coat of sealer has been applied.

Stain Application

A new slab must cure for 28 days before work is started. Depending on several variables such as the type of concrete,temperature, etc., stains can be applied in as little as 21 days.

When applying stain, 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 return to the area saves on cleanup, achieves abetter looking installation, and makes damage repair during the rest of construction easier to handle.

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

Sprayers are often used to apply stains, but they should be rated for acid and have no metal parts. Acid will quickly destroy metal parts, which can affect the color of the stain. Use a spray tip with a circular pattern, spraying in a pattern that goes from left to right and then from right to left, with someone scrubbing the stain into the surface using a medium-bristle brush in a circular motion just behind the spray. It’s important to scrub in the stain and not just push it around. An additional spray pass just behind the scrubbing removes brush marks. This method ensures good penetration and minimal marking from either the sprayer or the brush.

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

Stains applied by paintbrush will penetrate well,but care must be taken to minimize brush marks, which are not usually regarded as desirable effects. Whatever stain application method is used, be sure to carefully mask surrounding areas to avoid accidental staining. Acid stains can be difficult, and in some cases, impossible to remove.

The increased interest in chemical-stain finishes is in the direction of more subtle effects. 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 matter, 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 adding a concrete overlay prior to staining is the best solution for concrete surfaces that show damage or have been abused during construction. Commercial overlay materials can be integrally colored, textured, and stained to provide a new range of decorative possibilities. The overlays have high 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 an acidic pH will remain on the surface. This layer must be thoroughly neutralized with EnduraPrep Neutralizer 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, the use of a pH tester to test surface of pH is a good way to ensure that conditions are ready for the next step of applying the clear sealer.

Applying Sealer

Surface sealers for exterior applications should be acrylic to allow moisture in the slab to escape. Solvent-based acrylic generally performs better than water-based products for outdoor use. A good application procedure consists of two thin coats of either solvent-based or water-based acrylic clear sealer for best results. The best maintenance procedure is applying Endura Seal Floor Finish for general wear and a non-skid surface. This adds a sacrificial coat to your existing sealer coat and increases gloss. In high traffic areas you may consider using a high performance sealer. High Performance sealers (Epoxy & Urethane) are much harder than standard acrylics. Follow the directions on the label of your sealer of choice for application method.