Even with the best intentions and the most skilled stainer, concrete has a mind of its own, and sometimes, that does not show through until the sealer goes on.
We scraped the concrete, we put stain remover on the concrete, we grinded it, we hand sanded it, and all looked well. The stains were out, the adhesives were gone, and the surface looked great: perfect and primed for acid staining.
We followed all the steps - all the steps that we had done many times before - but this time was different. This time we could not see the problem. The stain went down well and the job was almost finished. The sealer went on and all was good.
But the next day, once the sealer had dried and we came back to check the project, there it was, spots all over the floor. We had used a mahogany stain, but the spots were of a faint brown color - not mahogany.
After all was said and done, we DID everything right, but we found the concrete had absorbed the stain and the sealer differently in those spots. And it made the job look less than perfect.
We did find a solution, which we had to put more sealer on those spots (about 2 coats more than the rest of the floor). This worked to a degree but those spots still came through, at no fault of the contractor.
So just know that it is not in the technique, it is in the concrete when you are thinking to acid stain a surface.
Does anyone have any other suggestions on acid stain technique? We have only used 1 or 2, but I have seen so many other ways of applying acid stain, and wonder what works best for you.