Recently I heard about people who actually want to "rust" their concrete. I had to laugh! I have a completely opposite situation. The rust started out as a stain of some sort. We laid the concrete over two years ago, and we're careful not to let oil, etc., drip on it. I don't know what caused the rust. It just showed up one day, got a little bigger over the past year (it's about the size of a cookie sheet and rust in color), and I have no clue. I tried a commercial product recommended by a hardware store, but it didn't touch the stain. How do I remove a rust stain from our concrete?

You've been very patient, and I appreciate your assistance while I've played Sherlock Homes and investigated your project. I thought it was odd that only one spot of rust appeared, and I'm relieved that you discovered two additional small rust spots in this area.

While your husband is very protective of his driveway, it appears that he's the culprit because he allowed the trailer with rusty safety chains to get wet by the sprinkler. Even if he only parks the trailer there a few times, if the chains get wet, rust will drip to the concrete and cause surface staining. The best solution is to immediately wash away the rust, then replace the chains or move the trailer.

Now, back to your question. Surface rust can be removed and cleaned using the following solutions in the order given:

One product that has given me good results is CLR. Follow the label directions, but if it doesn't work, apply it full-strength directly to the stained area and work it in using a scrub brush. Rinse thoroughly and repeat the process if it doesn't remove all the rust the first time.

Mix a solution of 1 pound of oxalic acid per gallon of water and mop it on the stained areas. Rinse off after three hours using clean water and scrubbing with a stiff bristle broom. Rinse thoroughly. This product is mildly toxic, so wear rubber gloves and goggles and keep a hose or bucket handy to quickly rinse off any that splashes onto your skin. Oxalic acid, otherwise known as wood bleach, is sold at hardware stores, paint stores and in some woodworking supply catalogs. A second application may be required.

Let me know which solution did the trick. If neither, I can recommend this next solution from the Portland Cement Association for deeper stains, but the stain needs to be severe. "Removing Stains and Cleaning Concrete Surfaces" can be found at www.cement.org/bookstore/index.asp (type document "IS214" in the search box). This 16-page document talks about different types of stains that can be removed and about cleaning concrete surfaces. The .pdf format is just $5.33, and the hard copy is $8.00. Solution 2 was one of three recommended in this booklet.

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C.R.S., Inc. · Spokane, Washington · USA