Polishing concrete is a fickle art. You’re basically at the mercy of how the slab contractor interprets the architect’s specification. This New Zealand contractor would like to tell clients that the imperfections pictured here are beyond his control, but without pointing fingers. He’d like our help.

After a decade in business, Queenstown Concrete Grinding has recently run into the same problem on some, though not all, salt-and-pepper grinds: a grid-like pattern of highs and lows under the cream that echoes the concrete’s steel reinforcement.

“I’m sure it’s just poor placing, but it’s hard to explain to owners that we can’t do a nice, consistent, light grind,” the note to [email protected] said. “They presume we’re just passing the blame on.

“We’re on a job right now that’s particularly bad. Despite advising the builder and owner that a deeper grind was required to even the discolouration/consistency, they’re still trying to blame it on my workmanship. It’s very frustrating.

“Is it unfair of me or is there another reason this may be happening? Perhaps the curing?”

We asked for photos. Not sure how much you can see in these three, but here goes.

Like any polishing contractor, Queenstown Concrete Grinding wants to give every client what they want. If you give the placement contractor (or architect, owner, or another party) guidelines for slabs that are to be ground and polished, please e-mail them to [email protected].