Working with Acid Stain for Concrete

It should not be that big of a deal to acid stain a concrete slab like this one, but being new at it complicated things for me. There are many videos on YouTube about concrete acid stain. Also there are water-based stains, but I didn’t even consider them because I wanted something that would last.

Freshly cured concrete takes a stain the best, which is what I was dealing with. In simplest terms, all you have to do is clean the surface, protect the surrounding areas, and spray the stain. They recommend using a pump sprayer just for acid but those cost around $75 so I went with the garden variety one I already had. I figured it would all be over in a few minutes- how bad could it get?

I bought a commercial grade acid stain (they all are) from a masonry supply place. Brickform, Blush-Tone Acid Stain in olive. It cost about $80 for a gallon. Their olive color is a light green, I wanted dark green but I could not find it anywhere. Applying a second or third stain would make it darker.BLAstainL

The first side of the slab went well, then I had to stop and pump up the sprayer and things started to get weird. Towards the end of the slab, blotches of rust brown started to dribble out, discoloring the slab. When it was done I thought, “Oh well.  I wanted it to have a mottled look and I got that.” In some places the stain looked great.BLAsatinR2

I did not neutralize the acid and let it go for a week trying to figure out if I needed to apply a second coat. You do not want to neutralize if you are going to reapply acid stain. The rust color was becoming more prevalent as the sun worked on it. Then I discovered light scrubbing with a wire brush would remove the rust color, revealing aquamarine blue underneath. The blue looked cool but this wasn’t a swimming pool. I realized I needed some advice so I called the manufacturer.

Acid Stain with rust color contamination. Color enhanced.

Concrete Acid Stain with rust color contamination. The color was enhanced in the photo for visualization.

At Rafco Products you have to leave a message for technical support and the guy calls you back. I think he was some kind of a consultant because it sounded like he was on a work site doing a job. Anyway he was concerned about the results I got with the rust blotches and said he thought I had some kind of contamination in the concrete finish. He said I needed to use a floor maintainer and a red brush to buff the slab and then reapply the acid stain. I had a vague idea what he was talking about and said thanks. I wondered if the brown tarp I used to cover the slab for a week while it cured was causing this rust contamination. Or maybe it was just old acid stain. The manufacture says the product should be no older than a year. This jug looked like it had been sitting around in a warehouse for sometime – I don’t know.

Following his advice, I went to the Home Depot rental department and picked-up a floor maintainer and bought 3 brushes- black the harshest, red is medium and white is the lightest. In the meantime I decided against buying more of the old product and went with Home Depot’s, Eagle, Jade, Acid Stain, available online only. It was $20 cheaper and I liked the green color a little better. I also did more research about acid stain and learned two very important tricks- the concrete should be damp before you spray and you can broom the stain around as it puddles and dries, working it in. You think it is acid and should stay the hell away from it but do not let it intimidate you- work it in!

I started the prep work on the slab with a red pad and plenty of water, then went to the black pad because I liked what the floor maintainer was doing to the cement. Take caution if you ever use one of these things: when I first turned on the floor maintainer it almost took my arm off doing a 360 degree turn and sucking up the power cord. What I learned is this: tip it forward and it goes one way, back it goes the other, find a happy medium and it stays in place.

Concrete slab after a good work over by the Floor Maintainer. Red and black brushes were used with plenty of water.

Concrete slab after a good work over by the Floor Maintainer. Red and black brushes were used with plenty of water.


The buffing took all the rust color off and muted the green way down, (the concrete was only four weeks old so I was removing the surface.) That was done in the evening and the next morning I made the concrete damp, sprayed on a gallon of the Eagle Jade Acid Stain, broomed in the puddles, and let it dry for 5 hours. I think the floor maintainer, damp concrete and broom made a big difference in the consistency of the color. My job was 185sq. ft. and one gallon was perfect.

Home Depots Eagle, acid stain in Jade.

Home Depots, Eagle, acid stain in Jade.

This application dried a much darker green and I was not thrilled with the color but they always tell you not to judge the color until the acid has been neutralized and rinsed off. It was a rusty medium green but consistent throughout.

Acid stain while still wet.

Acid stain just after application while still wet.


BLAstainBroomBefore I neutralized the acid I waited as long as I could for the stain to work but I needed to get the floor maintainer back for my 24-hour rental. I mixed 16 ounces of ammonia with 5 gallons of water and poured it around. Since I had the floor maintainer, I decided to use the lightest, white pad and buff the neutralizers around. I flood rinsed this off and mixed another batch of neutralizer, repeating the process. It looked great. A nice, mottled, medium green. The rust look was gone.

The crazy thing about this stuff is that, as the concrete surface dries, you get a different intensity of color- lighter as it dries. You need to pay attention to this because the 2 types of sealer you can choose from will make it look different also. Acrylic or water-based sealer will make the concrete look a similar color as when the surface is damp and the high gloss, oil-based sealer will leave it with a color similar to when the concrete is wet. I went with Home Depot’s, Eagle, Armor Seal, for $36 a gallon online. It is an acrylic based sealer that was easy to use and could be reapplied years later.

Acid stain close up detail of one of the more interesting areas.

Acid stain close up detail of one of the more interesting areas.

Finished acid stained concrete after one application of acrylic sealer.

Finished acid stained concrete after one application of acrylic sealer.

Now that I’ve done this, I would definitely do it again on an outside project. It is a great look. But because of all the flooding with water for rinsing, I decided against doing it inside the house on my kitchen and dining area’s thin, hydronic, concrete slab.

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