The purpose of spall repair is to repair deteriorated concrete, repair damaged reinforcing steel, and replace the lost concrete section.Spalls are typically caused by rusting rebar that expands as it rusts and ruptures chunks of concrete off of buildings. This is a big problem in Hawaii where the air is saturated with moisture and corrosive salt. Concrete is only water tight if rebar is placed well below the surface of the concrete. If placed too close to the surface rebar will rust even due to the moisture in the air. Spalls are more costly to fix than cracks. If at all possible crack repairs should be done early to avoid spalls. Concrete should be painted or coated to prevent moisture penetration.