Because of their similarity in appearance to cold joints, the horizontal lines (stratification) sometimes seen in cured cast-in-place concrete are frequently subject to criticism. Two methods utilizing vibrators have been devised to remedy the problem. Casting concrete in long stretches of wall forms is usually done in successive layers or lifts, leaving a line or stratification with each pass during the operation. This line is actually a zone of aggregate free grout that is created when the jitterbug action of vibrators causes the aggregate to settle. As would be expected, if the wall is sandblasted at a later stage this irregular line is exaggerated rather than diffused. The following technique has been used to eliminate a substantial percentage of these stratifications. Care in vibrating is a primary consideration. The vibrator head should not be allowed to come in contact with the form and vibrators should be kept at least four inches away form surfaces to be sandblasted. After a layer of concrete has been placed and vibration completed, the same aggregate used in the mix is sprinkled by hand onto the layer of paste approximately six feet behind the vibrator. To avoid honeycombing, however, care must be taken to avoid pileup during application of the aggregate. A homogeneous mixture is re-established as the falling rocks penetrate on impact and become embedded int he underlying layer of grout.