Applying Acid Stain

Before applying acid stain, read all product instructions and precautions. Acid based stain normally comes in one gallon containers. A gallon typically covers 200-300 sq ft. Age, porosity, weather, surface texture, and overall composition of the concrete will affect the coverage rate. Older concrete with a rough surface requires more stain than new, smooth concrete.

The first step is diluting the stain. Most brands of acid based stain recommend diluting to 1:1 acid/water. You can get just as much color with diluted stain so applying acid stain full strength would just be a waste.

When the surface is completely dry, start by brushing in any small areas with a nylon brush in a swift, circular motion. Then use a plastic pump sprayer or large nylon brush to apply the stain over large areas making sure not to leave any drips because they will be visible when it dries.

Spray in a circular motion trying to evenly cover the surface. If using a brush, apply in a circular or figure eight motion moving the brush swiftly and repetitively over the same area to avoid leaving brush marks. Since the acid begins reacting upon contact, the goal is to spread the stain as evenly and quickly as possible. You want to avoid having to overlap areas that have already dried.

Important: Applying acid stain is not like painting. You can't cut the edges with a brush and then stain the rest. The more stain that's applied, the darker the color usually gets.

So if you cut the edges and then overlap, this overlapping is very visible and unsightly. The best way to avoid this is to tape off the edges and cover anything subject to overspray. Or you can have someone hold a piece of cardboard to stop overspray.

Allow it to dry for at least 4 hours. If the first coat isn't dark enough, you can apply a second coat and use a stiff-bristled brush to work the stain in. When all coats have been applied, allow the surface to dry overnight to give the stain maximum time for penetration.

Tips

Before applying acid stain, always do a test in an inconspicuous area to see how it will look. If you think it's too dark, dilute the stain. If you get little or no color, you need to do more surface prep or consider a complete overlay.
For a more inconsistant coloring or marbleing, spray the surface with water first and apply stain with a brush in large circular motions.
If you're using more than one color and you're afraid of the colors running together, you can apply sealer over finished areas before staining surrounding areas. Acid stains won't penetrate through concrete sealers.
Use plastic sprayers and brushes because acid based stain may react with metal objects.
Take the proper precautions including rubber gloves, safety glasses, long pants and sleeves. You are working with a toxic and harmful product. Keep clean water close by in case of accidental splashes and spills. Always read the label for safety instructions.
Protect any walls, plants, or any other areas from overspray.
Apply when the temperature is between 50 and 90 degrees and the weather is dry. If its going to be a hot day, it's better to stain in the morning. You don't want it to dry too fast.
If you plan to spray, pick a day that isn't windy or else brush it on.
When diluting acid based stain, ALWAYS POUR ACID INTO WATER, NEVER WATER INTO ACID!

After the surface has dried, wash it thoroughly with a neutralizer. Baking soda and water works well for this. Mix 1/4lb of baking soda per 2 gallons of water and brush it around entire surface. Then rinse completely and let dry. For interior floors, simply mop up the excess water or suck it up with a wet vac.

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Applying Acid Stain