I had written a compete answer to this question, however can be more concisely answered with a simple link"Stucco a Masonry or Concrete WallTo apply stucco to an existing brick, block or concrete wall, first brush a concrete bonding agent onto the wall, then allow it to dry completely. After the bonding agent has been allowed to dry, the stucco can be applied directly to the wall. The application of the stucco should begin with a scratch coat, a 1/4 to 1/2 inch layer of mortar which is applied directly to the structure and allowed to slightly harden. After the mortar has hardened slightly, it should be scratched to a depth of 1/8" and allowed to harden for between 36 and 48 hours, periodically misting the surface to keep it moist.After the curing period has passed, a finish coat can be applied. The finish coat will be between 1/8" to 1/4" thick. The finish coat can be finished to the desired texture, then allowed to cure for another 36 to 48 hours, with periodic misting to keep the surface moist."