Common Causes: Concrete surface crazing usually occurs because one or more of the rules of "good concrete practice" were not followed. The most frequent causes are :

• Poor or inadequate curing. Intermittent wet curing or even the delayed application of curing will permit rapid drying of the surface and promote crazing.
• An excessive concentration of cement paste and fines at the surface caused by an overly wet mix, which allows coarse aggregate to settle.
• Bullfloating or finishing while there is bleed water on the surface or the use of a steel trowel sealing the surface and diluting the cement paste.
• Sprinkling cement on the surface to dry up the bleed water is a frequent cause of crazing surfaces. This concentrates fines on the surface.
• Concrete which contain a high percentage of sand fines will increase the water demand in the mix.
• Crazing may occur when water sprinkling is employed as a curing method. Care must be taken to insure that a continuous spray rather than an intermittent spray are used. Curing water that is much colder (20 degrees F lower) than the concrete can also contribute to crazing.

Prevention:

• Avoid high slump concrete - do not exceed ( 4 ) inch slump.
• Start curing as soon as possible. Damp burlap must be kept moist for a minimum of 3 days. A liquid membrane-curing compound is most common. A high quality cure and seal is best.
• Limit bleeding by increasing air entrainment in the mix.
• Limit troweling and don't trowel too early.
• On outside work use a broom finish whenever practical.
• Use the right amount of finishing at the right time. Do not perform finishing operations while there is excess moisture or bleed water on the surface.
• Dampen the subgrade just prior to concrete placement. If a vapor barrier, such as polyethylene, is required on the subgrade, cover it with 2 inches of damp compacted sand to reduce bleeding.