Cold Joints in Concrete Construction

From Ray

"What is a cold joint in concrete construction? I see a jagged line, almost a crack, in a new house I am thinking of buying. The inspector said it was due to a cold pour, creating a cold joint.
There doesn't seem to be any evidence of water leaks anywhere.

Hi Ray,

"A cold joint is the intersection between the end of one concrete pour and the beginning of a new pour.

The basic rule is to try to avoid cold joints by pouring straight through until the job is finished. The cold joint is a weak area and could allow the entry of water.

Note the reinforcing bars in photos.
If it must be done, inserting reinforcing bars in the fresh concrete of the old pour will tie in the new pour more effectively." NAHB Research Center.

If you see evidence of cold joints in an existing wall of a house and you don't know if there is rebar reinforcing in the wall, a concrete expert from a concrete supplier should be able to tell if reinforcing bars are in the wall using metal detection equipment.