How to Test a Rebar Installation

Measure the distance from the ground to the bottom of the rebar every few feet over the whole area of the form. If your project is a driveway, a patio or anything else that is in cast directly on the ground, the bottom of the rebar can be no closer to the ground than 3 inches. If you find any spots that are closer than this, replace the rebar supports with larger ones. If your project is not in contact with the earth, then the minimum distance from the rebar to the ground shrinks to 1½ inches.

Measure the distance from the top of the rebar to the top of the form, and also to the sides. If the top or sides of the concrete are not going to be exposed to the weather and your project is a slab, wall, joist, beam or column, then you'll need the bars to be spaced a minimum distance of 1½ inches between them and the edges of the form.

Measure the thickness of the rebar. If the bars are size 11 or smaller and the project is not a beam or column, then the distance can be as little as ¾ inch. Bars size 5 and smaller that are exposed to the weather need at least 1½ inches. Larger rebar needs at least 2 inches of spacing.

Measure the length, width and depth of the finished concrete product after it has cured. Run a rebar detector over each exposed surface of the project. Make sure the distances are the same as they were before the concrete was poured over them. If the bars shifted during pouring so they are closer to the surface than the minimum distances required, you'll need to seek professional advice before putting your project to use.

Add the thickness of the rebar to the reading of the rebar detector at the top of the concrete. Subtract this figure from the thickness of the concrete. The result is the distance that the bottom of the rebar is sitting from the ground. Compare this with your original measurement.