The toilet flange may be the cause of a toilet leak at the base of the toilet. Tightening the bolts will reveal a loose mounting bolt, leading to finding a broken toilet flange. A flange saver will fix it.
These flange savers slide under broken flanges and allow the closet bolt to grab onto the remaining flange. To install the saver, you slip the bolt into the saver and slide it under what is left of the flange. If too much of the old flange is missing you can try an inside-set toilet flange.
An inside-set flange can be installed without fancy tools or melting lead. It is slid into the cast iron drain and tightened to make a seal. You will have to check to be sure that the new flange does not stick up too high preventing the toilet from resting on the floor.
Once the flange saver or inside-set ring is installed place the toilet over the hole and try to rock the bowl back and forth. If the toilet moves, even a little bit, it indicates you’ll have to shim between it and the floor before installing the toilet. A rocking toilet may only leak a few drops of water, but it will cause floor damage because the trapped leaking water cannot evaporate.
Once the toilet shims are in place, tape them to the floor so they do not move during installation.
When installing a toilet bowl over the flange, expect the wax ring to make contact with the toilet bowl about one-quarter-inch before the bowl hits the floor. You may need two wax rings to make a good seal, especially if the toilet is shimmed very high.
Use only two fingers on the wrench when tightening the closet bolts. Many a closet flange is broken when too much force is applied. Use your body weight to help crush the wax rings before bolting down a toilet. Remember, a toilet is a china fixture, so take your time.
Trim the shims if they are protruding from under the bowl. Then caulk or grout between the bowl and the floor to finish this job. A latex mildew resistant caulk is used to fill any thin gap between the bowl and the floor.
If the gap between the bowl and the floor is larger than one-eighth-inch, use tile grout to fill around the base of the bowl. This will dry fast and hard, giving the bowl better support to the floor.