Is it necessary to wash the surface of a work joint before pouring the next concrete ? 

It is indispensable to clean the joint surface with pressure water before placing the wall formwork. This operation is to eliminate the cement film on the aggregates so that the new concrete adheres well on the old one. It is to be retained that the surface of the work joint must be water-saturated, in order to eliminate porous concrete above the joint. In case of strong wind or intensive sunshine, the concrete must be protected against premature drying out.