Toilet pipe not level with sub floor

halfmassive

First post but I've been reading the topics here like crazy lately. Already this forum has been a life saver!

I am mid way through a demo and renovation of a 1950s bathroom and have run into a problem.

The original floor had a 1" or so mud floor and unfortunately I wasn't able to save it. After tearing it out to the subfloor (12" planks) I have found that the toilet drain pipe (not sure of the exact term) which is the original cast iron does not sit flush with the sub floor. The original builders put a tin cover over this and there is a noticeable hump where this occurs. I assume this wasn't a problem for the original builders because it would have been mudded over and then leveled out.

I was planning on using 3/4" ply topped with cement board and then tile on that.

Now I can't lay my plywood directly over this raised area, so would my options be. I thought about cutting a notch with the plywood and then using some sort of mud or concrete to fill in the notch so I can tile on that. Another option I can think of is using 2 sheets of plywood with the notch on the first layer and them solid sheet on the second layer.

I don't have much experience with mud/concrete so I am pretty clueless about the best way to correct this, but would appreciate the help.

Thanks!

Here are a few pics:

bill01

Looks very suspect. You would think the slope of the pipe would take it under the floor more.

I bet the easiest is going to be cement. I would not just put a small fill between plywood I would at least go as wide as the metal. Although it won't get much walking on back there concrete in pretty fragile if you make it too thin or narrow. If it was me I would do that whole corner with concrete. I suspect you will end up with enough material just buying the minimum amount. There are videos on utube that show how to do this and how dry the mix needs to be.

joecaption

If it was my job I would go under the floor and snap off the old cast tail piece, cut out that board at least 4' from the wall were it would sit next to a floor joist. (make a note of where the drain pipe is so you can make a new hole in the subfloor.
Add a 2 X 4 nailer to the side of the joist and install a whole new piece.
If you plan on leaving those old board as part of the subfloor your going to have to go back and add two screws every place the board sits on the floor joist.
I personaly never use plywood for a subfloor in a bathroom. I use Advantec 3/4" T X G. Far more staple and water resistant then plywood.
I attach it every 4" on the edges and 6 to 8" in the field. I use screws not nails.
Since you still could use some more build up I'd go over that with 3/8 or better yet 1/2 subfloor rated plywood as an underlayment. Making sure the seams do not line up with the seams below. It also gets attached every 4" on the edges and 6 to 8 in the field.
Cut out the hole for the drain with a 4-1/4 hole saw. Now your ready for the 1/4" tile board set in a bed of thin set attached with tile board screws.
Once that's in place you can install a new flange with a tail piece and a hubless coupling. Now the flange will sit almost flush with the finished floor. Just use a thicker wax ring.

halfmassive

I think this is the route I'd like to take. Cutting the cast iron is way out of my skill set. Now do I need to do anything special the joints of where the mud will meet the plywood? Also should I use the mud to level the area out with the plywood or bring the mud up even with the cement board that I'll lay over the ply? Thanks again this is a real life saver.

woody4249

My guess is that the hump in the floor [or the metal] is the female band to the joint in the cast iron. I would pop up the metal and take a look.
Replacing the cast iron at this point can be tricky without a cutter, my suggestion would be to leave it as it is and just take up the metal sheeting.
I have come across this problem before and cut a recess or small opening in the substrate to go over this hump. When the concrete board is installed, then the tile, it will be strong enough. It is important however to get this flat so that the toilet will sit evenly when complete.
The other thing to check is the condition of the toilet flange. This would be the time to add another metal ring if the slots are rotted out. It's just a metal ring that you can bolt directly onto the original flange.

A tip here is to cut your substrate into manageable sizes. Once you have it screwed down and the concrete board installed it will all be strong enough.....just keep it flat and keep in mind adjacent floor heights and transitions.

Mike

__________________
"I'm not as green as I am cabbage looking"

woody4249

Oh............almost forgot.
Don't use 1/4" and 1/2" thick plywood and make the mistake that they equal 3/4" thickness in strength.....they don't.
I learned the hard way.

__________________
"I'm not as green as I am cabbage looking"

bill01

I am no expert having done this all of once. You want to at least cover the wood with tar paper. They have a special mesh reinforcement that you put in but it may not matter in such a small area. The key on if you put cement board over the mud or run the mud all the way to the top will depend on if the hump in the floor is deeper than the plywood. If you are lucky you can put the cement board over it which will solve the problem of the seam. If you run the mud the cement board level and then apply tile directly you get into the issue of the floor flexing differently enough to crack or loosen tiles. If you go that way I would plan very carefully so that joint at worst would crack some grout between tiles and not a tile.

You may want to think about a mud bed for the complete floor. I suspect the cost will be about the same when you are doing the labor. It is not real hard mostly just being careful to get everything nice and level. Watch some of the online videos, the key that seems very strange at first is how dry the concrete mix seems.

halfmassive

Thanks very much for the replies. All the advice has really helped me sort this out to the best of my abilities. I think I'm going to use 3/4" with a notch or hole cut out to avoid the hump. If I can keep this area relativly small I think I'll just leave the void alone and cover with cement board (probably hardie board). If I end up having to cut a full notch around the flange and the hump in the floor I'll probably give some dry pack mud a shot and then cover with cement board. Would filling the voided area with modified thinset be better or worse than using the deck mud?

And I'll also be installing a new closet flange - the old one was plastic and cracked.

Thanks again