I am in the process of replacing a WC in downstairs cloak. The old WC was bedded in with mortar onto a concrete floor. While chipping away the mortar the whole section lifted and has now left a hole in the floor. The hole is approx 1" deep in centre and diameter of WC pan base. The surface is also very crumbly. Is there a quick setting repair I can use? Or will I be able to get away with drilling down deeper and using frame fixings to secure new wc which has a bigger base than the old one. Many thanks