Concrete
Concrete Cover
The thickness of concrete between the outer surface and the nearest reinforcing bar, providing protection from corrosion and fire.
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In the Field
Cover is maintained with plastic or metal chairs/spacers placed under and beside rebar before the pour. Walking on rebar mats during pours often crushes chairs — inspectors check cover with cover meters on finished slabs.
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Rule of Thumb
ACI 318 minimum cover: 3/4 inch for slabs not exposed to weather, 1.5 inches for exposed slabs, 2 inches for beams/columns, 3 inches for concrete cast against earth.