Q: Our placing crew splattered concrete on an aluminum storm door when we were placing a patio. The splatters are several days old. I heard that concrete etches aluminum and need to know how to clean off the splatters without marring the aluminum surface.

We called an aluminum producer and they recommended using Soft Scrub, a bathroom cleaning product you can buy at a grocery store. They said this product will shine the aluminum and can be used to treat weathered aluminum.

To test their suggestion, we put a concrete splatter on an aluminum frame (photo A), then scraped it off with a metal hand scraper four days later (photo B). A cement film still remained after scraping, and we tried to remove it with a sponge soaked with Soft Scrub.

When that had no effect, we applied Soft Scrub directly on the cement film and waited a minute before wiping it off with a sponge. Neither of these methods removed the cement film (photo C).We next used extra-fine steel wool and succeeded in removing some of the cement paste. But the underlying aluminum was darker in color, even after we scrubbed it again with Soft Scrub (photo D). However, the Soft Scrub did shine up the aluminum that hadn't come into contact with the splatter. Removing the splatter sooner might have avoided the etching problem, but we didn't test the recommended procedure at an earlier stage.

Have any of our readers found an effective way to remove concrete splatter and prevent aluminum etching?

A:Readers Respond:

While in college, I was taught a technique by a concrete finisher that I have used with great results over the past 17 years.Purchase a cheap powdered laundry detergent, and mix it with just enough water to form a thick paste. Using a paint brush, apply the paste to the aluminum frame. (If the area is large, the paste can be applied with a roller.) The paste dries extremely fast and can be applied the day before or hours before a concrete pour. Any splatter can then be removed with a water hose, making the cleanup extremely easy.

The paste keeps the splatter from sticking and does not allow the concrete to etch the metal. In addition to aluminum, this process can be used for galvanized metals, block, brick and metal building panels. I have not found a product that the paste will not protect. I have even used it to protect glass block and glazed tile from mortar.

- Joe Ping Allco Inc. Beaumont, Texas.

We had a similar concrete splatter problem years ago. After removing the concrete, we scrubbed the aluminum with extra-fine stainless-steel wool and a mild laundry soap. (At the time, Soft Scrub was not yet available.)

- Bernard Anderson Building Inspector City of Kankakee, Code Enforcement Kankakee, Ill.

As a supplier of various aluminum construction products, my company has come across that question many times. The etching effect of concrete on aluminum happens only when the concrete is green, so if you wait several days before removing the splatter, it may be too late for optimum results. The only truly effective method is prevention. However, there are various products-all phosphoric-acid based-that will do a good job of removing old concrete stains. One brand name we have used is Thealum. These products normally are available from industrial-chemical suppliers.

- Pedro P. Giralt Giralt Enterprises Inc. Miami