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Birdbaths on Concrete Slabs

ASCC Position Statement #7

Owners, architects, and engineers have a variety of perceptions and expectations regarding birdbaths on concrete slabs. Birdbaths are small ponds or puddles of water that appear on a level or sloped concrete surface after a rain or washing the slabs (see photo). Many specifications attempt to eliminate birdbaths and often require a final water washing of the slab to check for birdbaths. The specifications require these birdbaths to be corrected by grinding or patching the slab surface.

Owners, architects, and engineers sometimes believe that birdbaths are a result of poor construction practices and can be eliminated. ACI 117-90, “Standard Specifications for Tolerances for Concrete Construction and Materials” doesn’t address the issue.

Eliminating birdbaths would require zero tolerances. The adjacent figure shows a birdbath at the valley of a slab surface profile under a 10 ft. straightedge. The tolerances shown are from ACI 117 and would indicate the maximum depth of the birdbath.

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