Q: We have to troubleshoot exterior flatwork problems including scaling. Is there any way to tell if scaling was caused by deicing salts and freeze-thaw cycles or poor finishing methods?
A.: An inadequate air void system can cause scaling of concrete exposed to freezing and thawing and deicers even if the concrete is finished correctly. Having a petrographer check air void characteristics of the hardened concrete will tell you if there's a problem with the air void system. Some scaling is caused by poor finishing methods and may occur even if the concrete is properly air entrained or isn't in a freezing climate. Called sheet scaling or delamination, it can be traced back to closing the concrete surface by troweling before bleeding has ceased. Bleedwater causes a weakened plane when it collects under the thin layer that's densified by premature finishing. Examine pieces of the mortar that have scaled off. Mauro Scali, senior petrographer for W. R. Grace & Co., says that if the scaling is caused by premature finishing the top of the piece will generally be darker and the bottom of the piece will be lighter in color. When scaling is caused by low air content, the top and bottom of the pieces are usually the same shade of color.