Popouts are pits left in the concrete surface after concrete has broken away due to localized internal pressure. Most often, they are caused by pieces of porous rock, such as chert, weathered dolomite, or shale, that are highly absorptive and have a relatively low specific gravity. If these aggregates become saturated and freeze, they either fracture due to internal pressure or push enough water into the mortar cover to cause the mortar to pop off. Popouts typically range from about 1/4 inch to several inches in diameter, and usually a portion of or all of the aggregate that caused the popout remains at the bottom of the hole.