View Full Version : Toilet flange in slab questions

03-09-2010, 03:29 PM
I got a bathroom re-mod job going on and with all the reading I've done I'm starting to wonder if I have a weird case on my hands and if it needs more attention than I first thought.

From all my searching everyone states to make sure the flange is secured to the subfloor to eliminate future issues, etc. But with my case it's a slab with CI pipe coming up, but the slab is all broke out around the pipe so the pipe & flange are just floating. I would think that this wouldn't be an issue as the toilet will sit on the slab but because it's unlevel around the opening and I'm getting ready to tile so I know I need to use some SLC to provide a stable surface.

So my questions are:
1) Does the area around the pipe and flange need any attention? Filled and secured, etc.?
2) Any advice on using SLC around this area? I've never used the stuff so I wondering how I'm going to keep it level and not falling & filling the void around the pipe.


03-09-2010, 04:39 PM
SLC will flow through any small crack. It isn't the best thing for the task you are interested in, I don't think. SLC won't bond existing poor concrete back together.

03-10-2010, 08:17 AM
IF those are roots I see around the pipe, be sure to fill the void with salt or root destroyer solution before sealing the concrete. I do NOT screw the flange down to concrete slabs, and since yours it cast iron, it would not need fastening regardless of where it is. Just fill the void with a patching concrete mix and tile, unless the floor is so uneven that the entire area needs to be resurfaced.

03-10-2010, 08:52 AM
thanks for the replies...

No, not roots... just debris from cleaning up and a bad pic.

I'm not worried about the void around the pipe if it's not an issue leaving that way with the flange, etc. But where the base of the toilet will meet the slab it isn't level. I need to build that up to tile and not sure if using SLC is best as it slopes right into the break out/void, or maybe just patch cementing the void and bring it up to level out the existing slab?

What would everyone suggest?


03-10-2010, 10:04 AM
How much out of level are you talking about? If it isn't too much, after you patch the hole, even thinset could be used if it's not too much. A medium bed mortar can go to 1", a normal thinset only about 1/4" (in one lift). If the whole bathroom is out of level, then flooding it with slc may be a good choice, but not for a small area. Note, for tile, it should be flat, but level isn't as big an issue - nice, but not necessary. If you wanted to use SLC, you'd need to plug any holes - foam, or something like that you stuff into them or cover over with would work. At doorways, I've used a board with some duct tape lapped slighltly into the room and up the board. Sill seal, as used under the sill plate on top of the concrete is a good thing to use around the permimeter of the room - you shouldn't run it up tight against the wall.

03-10-2010, 12:01 PM
It needs about 1/2" - 1" in the areas right around the pipe. It's not that it's unlevel but more broken out if you get my meaning.

I've drew a line on the pic to illustrate where it's low.. the rest of the floor is level and ready to go.