The present invention is directed to a method and system for preventing intrusion of viscous poured concrete into electrical or telecom boxes using resilient members having a top surface that fills the surface opening of the box it is inserted into where the spring back of the resilient member insures a proper seal around the surface opening. An example method for preventing intrusion of poured concrete into a box comprises selecting a suitable member for insertion into the box, compressing the member, inserting it into the box, and pouring concrete around the box. The resilient member may subsequently be removed and reused in another box. In another example method, a supply of resilient members of different shapes and sizes is provided for insertion into differently sized boxes.