Things You'll Need
Masonry drill bit
Toilet flanges provide a stable surface that the toilet grabs onto through retaining bolts. The flange is secured to the floor through anchor screws driven into the flooring. Replacing a flange typically requires removing the retaining screws and installing a new flange. Cement floors present the most difficult medium for replacing floor flanges. Removing the flange is relatively easy. You simply unscrew the retaining screws and pry the flange out. Depending upon the surrounding material, installing the flange can be relatively difficult.
Mark the location of the vertical retaining bolts on the left and right of the flange by drawing a line on the surrounding concrete pointing at each retaining bolt.
Remove the existing flange by unscrewing the anchor screws and prying the flange out of the pipe.
Place a scrap piece of drain pipe of the same size as the existing drain pipe on top of the existing drain pipe. You can measure the inner diameter of the existing pipe to determine the proper size. The scrap piece of pipe needs to extend beyond the surface of the floor to protect the existing pipe.
Mix together leveling compound, following directions on the container. Spoon the mixture around the scrap piece of pipe with the tip of a trowel to fill in the existing screw holes and any other damage to the concrete. Smooth the compound over with a trowel so that the compound is flush with the surface of the surrounding concrete. Allow the material to set up partially.
Rotate the scrap piece of pipe while the compound sets so that the leveling compound does not adhere to the pipe. Remove the pipe after the compound has fully set.
Press the new flange into the drain pipe opening. Position the flange so that the marks on the left and right line up with the ends of the channels in the flange. Mark the position of the screw holes. Remove the flange.
Drill pilot holes using the masonry drill bit included with the cement anchors and a hammer drill. Position the flange with the pilot holes lining up with the screw holes in the flange. Drive cement anchors into the flooring with the hammer drill. Wiggle the flange to ensure that it is stable and secure. Tighten the anchors as needed.