This is a 3-year-old concrete slab in a garage out in the country off of a dirt road. You can see all of the dirt and gravel that has accumulated on the unfinished floor. In preparation for acid staining, we cleaned the floor with detergent and a rotary floor machine. When it wouldn't dry, we set up a "tenting operation" using a dehumidifier (above right).
"Tenting" is an effective means for quickly drying concrete after flooding. It forces warm, dry air, in a confined space, over damp concrete. After a week, we tested the moisture content again, but it still wasn't drying - see the shadowing caused by the dampness (above left). Ultimately, we had to grind off the dense cement paste on the surface to open up the pores of the concrete and allow the concrete to dry (above right).
Normally, grinding is to be avoided when acid staining a concrete floor - it removes the cement on the surface, that the acid stain reacts with, and exposes fine to medium size aggregate. In this case, however, we were still able to get a very good staining result (above left). Maximum fullness and depth of the color was then achieved by applying 2 coats of a clear polyurea sealer (above right).
The above two photos show the beginning and concluding condition of the floor from another perspective. The floor does not have a deep "wet look", like many interior acid-stained concrete floors, because we had to add non-slip aggregate to the clear coating as a safety precaution for wet condtions. This aggregate is not visible, but it does reduce the gloss of the floor to a "satin" sheen.
Also, the natural mottling effect of the color seen on this floor is something only achievable through the use of acid stain. Dyes and water-based concrete stains available at big box and paint stores will not product this look. Metallic epoxy, a popular new product for concrete, will produce a similar "flowing" effect that many people like, but it is not as"natural" looking.
One reason such other products are preferable to acid stain, in many people's minds, is because of the problem you see in the photos above and below left - if the concrete is not perfectly "clean", the acid stain will not react, and you may see patches of non-color, or "blemishes" across the floor. Dyes, water-based concrete stains, and metallic epoxy cover and conceal spots like these.
A skilled, experienced, and professional acid-staining contractor, however, can still make these "blemishes" or "inconsistencies" disappear, as we did with this spot, which was caused by hydraulic fluid leaking from the vehicle kept in the garage. We used solvent-based pigment dispersions, mixed with clear polyurea, to match the color of the floor. This type of "faux-finishing" can be done so well that all traces of the original blemish are permanently removed.