Q.: We have the job of cleaning mortar splashes over a lot of nearby galvanized hardware on stadium seats. We know that sulfates attack cement products. If we were to apply some kind of sulfate solution to the splashes would it remove them? If so, what kind of sulfate solution would you recommend?
A.: Probably Glauber's salt (sodium sulfate, Na2SO4 10H20) would be the best because it would not be aggressive to zinc and is soluble up to about 9 parts of salt in 10 parts by weight of water. You might try as concentrated a solution as convenient. It would be desirable to apply it in warm or hot weather and to apply a curing compound to keep the mortar from drying out. We don't know how fast it would work on your mortar splashes, however.
Note: In a followup to this inquirer, Concrete Construction learned that if there were any results from the sodium sulfate solution they were not fast enough to be practical. The contractor also tried penetrating oils without success. An attempt to remove by heating melted some of the zinc. Wire brushing was ineffective. Waterblasting at 3000-psi pressure did not do any good. The contractor finally removed the mortar by sandblasting, but the metal then had to be regalvanized.