Acid rain is rainwater that has combined with automobile and smokestack emissions in the air to form sulfuric or sulfurous acid. Pitted with soot and grime, countless structures suffer from this unsightly, caustic (and costly) disease. Absorbed into the pores of concrete and masonry, acid rain attacks the concrete and eventually may corrode the steel. Reinforcing steel expands when it rusts, causing scaling, spalling and cracking of the concrete. Paint on the inside of buildings has even peeled because acid rain forced by high winds penetrated so deep.
A patented coating system that is reportedly both weatherproof and acid-proof was created for use on old or newly constructed buildings. Basically a polymer-modified acrylic resin in liquid form, this clear plastic coating is said to protect against atmospheric chemicals and graffiti and to reduce heat loss when used on exterior building walls. Unlike many coating systems, this sealer is injected into the concrete using a specially designed air injection machine that can force the liquid sealer as deep as 2 inches into a concrete block wall.
One structure on which this protective coating system has been used is the 3-1/2 story high "Bust of Sylvette", a prestressed concrete sculpture at New York University. Built only 15 years earlier, the concrete structure was already deteriorating from acid rain. The same protective coating system was also used on several New York University buildings, including two 30-story apartment buildings, a sports arena, and the 70-year old brick law building. After testing by the National Bureau of Standards, this system was also used on the sandstone of the U.S. Capitol Building's west wall.