Cold joints occur when new sections of concrete wall, floor, footing, ceiling are poured in relations to existing concrete sections. These locations are prone to leaks. An example of a location where the cold joint might leak is in the cellar where the concrete porch slab connects with the cellar wall. These corners can be injected with either epoxy resin or polyurethane resin We use the highest grade materials (AquaPak and AquaBlue Flexible Grout) whereas most concrete crack repair companies budget their material cost expendure to keep profit margins high. Most companies don't even inject epoxy for this reason, but if you ask any structural engineering firm, the recommended repair for any concrete foundation wall or cold joint is epoxy resin.