Question: I know that concrete has to be vibrated. Does grout have to be vibrated as well?

Answer: To ensure that the grout space is completely filled, grout needs to be vibrated when it is placed and just before the grout sets.The Uniform Building Code (UBC) requires that grout pours greater than 12 inches be reconsolidated by mechanical vibration. Grout pours less than 12 inches can be puddled.In its Technical Notes 17D, "High-lift Grouted Reinforced Brick Masonry," the Brick Institute of America (BIA) recommends a procedure for vibrating grout when high-lift grouting: Consolidate each grout lift by vibration within 10 minutes. Then, after the lift has become plastic but before it sets, pour the next lift of grout. In addition to vibrating the full height of this next lift, extend the vibrator 12 to 18 inches into the preceding grout lift. Some people recommend 18 to 24 inches. Vibrating the previous grout lift in this way eliminates the air pocket left after water is absorbed by the masonry units.