Converting fiberglass shower(on slab), should I embed drain ABS in concrete?

Hi,

I am in the middle of a 1/2 bath remodel which consists of replacing a fiberglass shower surround with backer and tile and a mud pan. After demoing the old surround, I found that the original construction method was to leave a 12" x 15" opening in the poured slab for the P-trap and drain riser (see the attached pic).

Since I'm going to be installing a mud pan, should I just encase everything in the hole in concrete before I start? Should I fill gravel in the hole up to the bottom of the existing slab, or does it even matter....should I replace the old trap while I have the opportunity? The house is almost 40 years old and in San Diego (no frost etc).

Thanks for any advice!

-frank

If the drain is in the right location, there's no reason to replace the p-trap.
You will need a clamping drain for the mud set pan, and after that is installed, you will need to pre-slope the base, which will include filling in the hole.
With a standard enclousure or fiberglass pan, the box out is fine and how it's done. Not so fine with mud set. The concrete mud based pan will be the support.

Thanks for the quick reply Terry. I'm actually using a Dix systems kit, with pre-pitch, then their one liner, then quick-pitch on top. I need a level slab to start with, hence my question about filling in the box out with concrete, encasing the existing ABS.


The drain is in the right place, but I need a little more height on the riser. I figured starting fresh with a new p-trap and riser would be better than doing a coupler and a bit more straight pipe on the riser.

I would fill with crush and then pour to match the existing slab thickness.

You have enough height to cut the riser, use a coupling, and get it the desired height. Or, buy a rambit, ream out the pipe in the socket, then glue in a new riser. If you haven't looked at it, check out www.schluter.com and review the Kerdi shower system. You can use your pan sloping aid, but you only need one layer...the preslope is tiled to with the membrane on it and the special drain that the membrane adheres to. this makes a totally waterproof system with a surface membrane right under the tile. Either way, conventionlal shower or Kerdi, or other, check out www.johnbridge.com for help with tiling. They have an extensive 'Liberry' with help and tips, and a good very active forum to answer your tiling questions.