Q: What is the best way to remove the white calcification from my colored concrete patio? We have very hard water here, and the sprinklers spray onto the patio. Lime-Away doesn't do much good.
A: If the "calcification" is calcium salts from your water supply, you should be able to remove them with a 10% solution of muriatic acid, which is available in most hardware stores. Put the 90% water in a bucket and add the acid to it. It's best to wear rubber gloves. Wet the surface lightly and scrub some acid mix into it with a deck brush. You should see the acid mix fizz. When the activity dies down, wash the area immediately with water so that the residue doesn't dry beforehand. When you see the acid begin to expose sand on the surface of the concrete, it's time to stop.
If calcium salts are coming up from the concrete, the problem might be more difficult to resolve. When these salts are deposited on the surface for a period of time, they take carbon dioxide from the atmosphere and form very hard calcium carbonate compounds. Acid will remove some of it but typically not all of it. You also can try scrubbing with a strip pad. If you can get the salts off, put an all-acrylic sealer on the surface. That will make any further problem with calcium salts easier to deal with. In the October 2001 issue of Concrete Construction, there is an article about efflorescence that you might find useful.