The Concrete Network
Question:

I get very different answers on how to properly prepare a power-troweled concrete surface for application of acid stains. Some people say never to use an acid wash to open the pores for staining and others say it's OK to use an acid wash of 10 parts water to one part acid. Who's right?

Answer:

As a general rule of thumb, you shouldn't use an acid wash to prep for an acid stain. Acid etching will destroy the cement paste that is needed to develop the stain color. The only time I recommend using an acid etch prior to acid staining is if the surface is superhard with a dense, burnished finish. Other types of stain that aren't acid-based, such as acrylics, may also require acid etching before application. To determine what type of surface prep is required, do a stain test first.

In my opinion, a 10:1 water-to-acid wash ratio is way too strong and will destroy too much of the concrete paste. I always recommend starting at 40:1 for any type of acid etch.

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