What I learned about acid etching

[Coloshaver]

My shop was completed 39 days after breaking ground. (I'll post some pictures when I get stuff moved in) I've decided to do a clear urethane floor sealer and needed to acid etch my 30'x50' floor. I found muriatic acid at Home Depot and bought a $10 garden sprayer from HF. It is cheaply constructed, but if it died I wasn't out much. The sprayer held up fine and after thorough rinsing may get to do bug spray duty. To etch concrete the label on the jug said to mix 24oz of acid to 1 gallon water. A gallon of acid (~$8) did my floor.

My biggest learning was where to start. I figured I'd do it like you would paint - start at the far corner and work out. I planned to do a section at a time using the saw cuts as boundaries. I got the first section done and realized that when I rinse it, I would have to push the water across the yet-to-be done sections and then have to wait for them to dry

So, if you plan to do it, start on the sections closest to where you push your rinse water. That way, the yet-to-be-done parts stay dry and you double or triple rinse the parts between you and your water exit. I figured this out after the first one and the rest went like clockwork.

Be careful and follow the instructions with the acid, but it is really pretty easy.

[Parc Ferme]

Did you have to go back and spot etch any areas? I had a few areas that remained smooth, and to be redone.

What was your nutralization method?

[Coloshaver]

Originally Posted by Parc Ferme

Did you have to go back and spot etch any areas? I had a few areas that remained smooth, and to be redone.

What was your nutralization method?

I have looked over it and didn't see any areas that stood out as being smooth. It was hand troweled and took 4 truck loads (pumped in) so there was some variation in the color and smoothness. I tried to get a pretty uniform coating from the sprayer.

The chemical reaction that causes the effervescence begins the neutralization process. After that, I used lots of water. I power washed and squeegeed each section when I was done and then went over the whole floor one last time.

[Cruzin90]

It's almost easier to just diamond grind than to acid etch correctly.

You need to scrub away any efforescence (which is typically salts). Salts are corrosive. Neutralize the acid with a small amount of baking soda in the water to make sure you stop the acid/base reaction.

[ptaylor2000]

The directions on the acid I bought said to dilute 1:20 with water. I mixed the acid at that concentration and got no etching.

I kept adding acid and sampling the solution until I got bubbling on the old concrete: the final solution was about 1 quart to a gallon and a half of water.

My concrete slab is about 80 years old; I don't know if that made a difference.

Paul in San Diego