Gours

Concrete derived micro-gours

Rimstone or gours can be formed by the secondary deposits derived from concrete, lime or mortar. These secondary deposits consisting primarily of calcium carbonate, are called calthemites and mimics the shapes and forms of cave speleothems to create stalactites, stalagmites, flowstone and gours. Gours form beneath concrete structures on a floor with a gradual sloping surface or on the side of rounded stalagmites derived from concrete. Most of the calcium carbonate carried by the leachate is deposited as stalactites (when the drop rate is slower than one drop per minute), leaving little in solution to be carried to the ground to create stalagmites, flowstone and gours. The leachate which does reach the ground usually evaporates quickly due to air movement beneath the concrete structure, hence micro-gours are more common.