Replacement of Metal ring on closet flange and filling holes
We bought our current home about 2 months ago. Last week, I went to replace a toilet on the first floor of the house. The toilet rocked quite a bit, but didn't think anything about it at the time. Removed the toilet and of course the seal on the wax ring had broke. The metal ring on the flange was rusted so I removed it. I have a replacement ring ready to go, but I have a question before I do.
It is an offset closet flange and water had been setting around the flange for a while. Although it never leaked to the exterior of the toilet, it did do a fair bit of damage to the mortar and concrete surround the flange. Meaning that some of it was so saturated that it just crumbed when I poked it with a screwdriver. That has been cleaned up, but now I have a small divot in which the flange sits. I was planning on mixing up a little concrete to fill the divot. Is this a good idea, bad idea? Should I fill with some other substance? I just don't want a reservoir for any future leaks.
TIA for your help,