What is a 'cold joint' in concrete?

A cold joint forms when a batch of concrete begins to set before the next batch is poured against it, preventing the two layers from intermixing. This creates a plane of weakness and a potential path for water leakage. Cold joints are common in large pours or when delays occur on site. We repair cold joints by drilling and injecting them with low-viscosity resin to bond the layers and seal the interface against water ingress.