Rear Flush Toilet

Having a couple of issues re-setting this toilet. The new floor is tile on top of cement board on top of a concrete slab. The finished floor height is very close to what it was before (within 1/16th inch). There is no wood sub-floor. So, I need to:

1. Figure out a way to secure the toilet to the floor (see pic). Keep in my mind that the floor is tile / cement board / concrete slab – no wood sub-floor. And, I must also secure the bolts on the back of the toilet (2) to the wall mounted flange at the same time as the floor (2) bolts / studs / ??? These floor mount holes will need to be a precise drilling or else all four bolts won’t line up. How do account for the squish of the ring to precisely mark for the floor bolts?

2. Determine if this is the proper wax ring for this application. It is a standard Home Depot #3. Seems like the plastic flange is a bit small compared to the wall pipe and doesn't create a snug fit. Does this look like the right wax ring? Is there a special ring I don’t know about? This toilet config. & equipment is from 1972.

No plumbers in the area have ever seen this type of install before and are of little or no help.

Lastly, the drain from my clothes washer seems to back flow though this drain pipe towards the toilet (moderate amount). Will this wax ring be a sufficient barrier to water flowing in both directions?

Any help appreciated,

Thanks,

Depending on the tile, you may need a diamond bit to drill a hole through. You have several concrete anchors you could use - lead, plastic, or a direct screw like a Tapcon. It helps if you put some tape on the floor, mark the holes, then drill. Another trick is to drill the guide a holes through a board, you could use the toilet as a template, hold the board down on the floor with someone standing on it, and use those holes as guides to start your holes.

A word on the way the tile was layed down for others...No cement board manufacturer allows it to be installed over cement. The board must be screwed or nailed down to fully embed it in the mortar underneath it. Hopefully, you did use mortar underneath it, for it might have a chance of surviving. Cement board is not very strong, is used as a decoupling layer between wood and tile. If there are any voids under the cbu, and you get a point load on the tile, you will likely have cracks and possible debonding occur.

There is one hybrid board that is designed for cement floor application - Wediboard. It is the only one I'm aware of, there may be others. But, all of the traditional boards like Duroc, Hardibacker, etc., are not designed for this application.

The rest of the toilet install looks fairly standard to me.

toilet

There is a specific wax ring made for back outlet toilets, and that one is not it. The proper one does not have the funnel, and does have a "felt" ring inserted in the center of the wax. You dry fit the toilet and mark, (and drill), the floor holes, then assemble the toilet to the wall, and finally insert the screws into the floor.

Securing cement board to slab

I used a hammer drill with a cement bit to drill through the cement board and into the slab. Then used countersunk capcom cement screws to attach the cement board to the slab, making sure the heads of the screws sank just below the surface of the cement board... Hope that works

Special Wax Ring

Oh, by the way, anyone know where to find that special wax ring mentioned above??

ring

Any halfway decent plumbing supply store. I don' t remember what its number is.

If you didn't use mortar under the cbu, your floor is at risk. Any void under there could result in a crack or debonding. Were you trying to raise the height of the floor? There are much better ways than putting cbu down on a slab that follows the manufacturer's instructions and would gain you a warranty. What you did won't.

Well, my main goal was to keep the finished floor height the same. If you notice from the pics, the toilet has to mount up directly in the receiveing pipe in the wall. If too high or too low, she won't fit right. The original config was 5/8" plywood with a shitty vinyl tile (about 1/32") glued on. Therfore, I had to keep the floor height right around 5/8". I used a 1/4" cement board with a 3/8" tile. Plus the thinset, that leaves me right about where I was before.

I really would love to get rid of this whole rear flush config so I could do this remod right...

Anywho, just trying to get her bolted up and get this bath back up and running!! - Almost there

You should be able to use the spec sheet available on the manufacturers website to accurately layout the loction of the floor anchors, then predrill for whatever anchor and fastener you choose.

The neoprene gaskets used for wall hung toilets would probably work ok for these as well.