Hi
I am replacing a cast iron tub with a tiled shower in a 3rd floor condo with a suspended concrete slab floor. I will be making the shower pan the traditional way with a pre-slope, waterproof membrane, layer of deck mud, then tile. The slab is 6 in thick with a 12 in void underneath, then the ceiling of the lower level. The slab has a 6 in hole drilled on one end where the drain pipe comes up, then a notch (3 in deep), 6 in wide and 12 in long where the drain pipe 90's and runs horizontal to the actual drain. So, I've removed the tub (breaking with a sledge hammer) and removed the old drain assembly down to a 2 in cast iron p-trap in the void under the slab. My new tile shower drain, with a 90 attached to it is about 6 - 8 in high. If I install this in the existing notch in the concrete, the drain height will be about 6 in above floor level in the bathroom. I want the drain height to be level with the concrete floor. To do this, I will have to break out more concrete, basically turn the 6 in by 12 in notch into a 6 in by 12 in hole. This won't be a problem, but I'm worried about filling the hole after the drain is set. I'm not sure how to make sure the concrete I fill the hole with will be strong enough to hold wieght. (I worried that the new concrete will just break through if enough weight were on it.) Any advice is much appreciated. Also, anyone know if ABS can be set in concrete, or do I need to put some sort of barrier between the ABS and the concrete.

Thanks alot

Have you run this by condo management?
As you are altering the structure of the core slab I would highly suggest you get approvals first before breaking up any concrete.

That's a good idea Randall. I'm think it'll be fine because many of the units have already had this done (strange though, none of the workers or contractors that did any of these showers are available .... some quit, some got fired...hmm)

If I do get approval, any idea on how to form the bottom of the suspended slab (I have no access to the void below)

I've heard of squirting expanding foam into the hole, but it seems to me that it wouldn't hold the wieght of the mud...

Also, do you know about setting ABS in concrete?

Thanks

Jon

I had to do something similar on a slab a couple of years ago. I'll try to explain the process for you.

I drilled holes into the slab on all four sides of the hole and cleaned the dust out of them with compressed air. I then filled the holes with a premium construction adhesive, then inserted rebar and allowed it to dry overnight.

Now let me backtrack a little. Before inserting the rebar, I took a piece of plywood that was slightly larger than the hole, which was about 6"x14" in my case. I drilled a hole in the center of it, then put the plywood through the hole (diagonally, of course) and inserted a lag bolt that was about 6" longer than the depth of the concrete. The plywood was held against the underside of the slab with the lag bolt going through a 2x4 on top of the slab and a nut over the 2x4.

Once the rebar, plywood, lag bolt, and 2x4 were locked into place, I put Quikrete 5000 psi concrete in the hole and finished it off as slick as possible, given the 2x4 that's kind of in the way. You might get around that to some degree by propping the 2x4 up on some blocks on either side of the opening. The floor won't have to be perfect, though, since you're going over it with deck mud.

Let it dry overnight, remove the nut and the 2x4, then cut the excess lag bolt off with a hack saw (I used a metal cutting blade on a reciprocating saw).

thanks kman...
that's sounds like the way to do it. I was actually able to avoid the situation when i looked at it again this morning. The owners actaully wanted the drain close to the wall, so by chipping just a few inches more out of the channel, i was able to fit my new drain assembly into the old drain hole.

so now, I still have a couple questions.

what's the best way to pack mud around the drain? when i took out the old drain, there was some foam and a bunch of pieces of a concrete bag stuffed around the pipes (i guess that's how they kept the mud from falling into the void below the slab.

do i need a barrier between ABS and concrete, or can I just pack the mud around the pipe?

thanks for the advice