How to Finish a Basement Bathroom – Part 2

How to finish a basement bathroom: Mark the floor layout for the shower stall, toilet and sink. Cut the concrete slab floor to relocate and install the shower drain.

This project is continued from How to Finish a Basement Bathroom – Part 1.

Basement Bathroom Layout: Toilet, Sink and Shower Stall

The next task is to decide where the bathroom fixtures – sink, toilet and shower stall will be installed. The builder had already roughed-in the plumbing so I didn’t have a lot of choices but it’s necessary to measure and mark the locations to check clearances and guide the work.

  • I verified the toilet plumbing rough-in dimension (distance from the wall to the soil stack) because this is an essential measurement for ordering the right toilet. In my case, it was a standard 15 inch rough-in distance from the wall.
  • I discovered that the builder placed the shower drain plumbing rough-in too close to the toilet soil stack, meaning the toilet would be too close to the shower. The shower drain will have to be relocated.
  • The width of the shower stall is limited to 3 feet due to the placement of the soil stack and clearance for the toilet.

I measured and marked the dimensions on the cement floor as shown in blue:

Basement Bathroom Plumbing Rough-in: Floor Blueprint

Basement Bathroom Plumbing Rough-in: Floor Blueprint

Basement Bathroom Shower Drain Plumbing Rough-In

The basement bathroom shower drain is off center and had to moved by several inches beyond the rim of the existing opening made by the home builder in the cement floor. A hammer drill and masonry bit is used to make holes for a knockout in the concrete slab floor to relocate the shower drain.

Basement Bathroom Shower Drain: Drill Holes for the Concrete Slab Knockout

Basement Bathroom Shower Drain: Drill Holes for the Concrete Slab Knockout

After drilling several holes to weaken the concrete slab floor, a brick chisel and sledge hammer are used to make the remaining cuts and shape the sides. Be sure to wear your safety glasses because cement chips fly everywhere.

Basement Bathroom Shower Drain: Cut the Concrete with a Brick Chisel

Basement Bathroom Shower Drain: Cut the Concrete with a Brick Chisel

Here’s the finished cut in the cement floor to relocate the basement bathroom shower drain to middle of the yet-to-built shower floor:

Basement Bathroom Concrete Floor: Shower Drain Plumbing Rough-in

Basement Bathroom Concrete Floor: Shower Drain Plumbing Rough-in

Basement Bathroom Shower Drain: P-Trap or S-Trap

I need to determine if the home builder has already installed a P-trap for the shower drain; if not then I must install a P-trap to prevent sewer gases from wafting up from the drain. I dug out the dirt around plumbing rough-in, sawed off several inches of vertical pipe (see above photo and compare to the following picture), then shined a flashlight into the PVC drain pipe. I saw what appeared to be trap (bend) in the drain and some dirt and PVC cuttings in the bottom, but to be certain I filled it with water which rose to a certain level and remained steady as I poured more water in the drain. I was now confident the builder installed a P-trap below grade because there’s hardly any room here for a P-trap. There is room for an S-trap but those are illegal per the Building Code and will siphon water allowing sewer gases to rise out of the drain. (Update: After finishing the bathroom, everything has worked perfectly with no sewer gas odors – I got down on my hands and knees to sniff around! I also noticed the water level in the toilet moves slightly up and down when the sewage pump runs indicating the plumbing traps are sealed and working.)

The PVC drain pipe 45 degree elbows are dry fitted before gluing to ensure the shower drain is correctly aligned:

Basement Bathroom Shower Drain Rough-in: Dry Fit the PVC Drain Pipe

Basement Bathroom Shower Drain Rough-in: Dry Fit the PVC Drain Pipe

The PVC pipe and shower drain base for a tile floor are glued together. The shower drain clamp ring, adjustable barrel and strainer are shown here. The shower drain flange (base unit glued to the PVC drain pipe) must be high enough above the concrete slab floor to be even with the primary mortar bed for the tile shower. I didn’t want to too shallow mortar bed so I installed the drain base maybe an inch to 1-1/2 inches above the floor. The shower mortar bed will be installed and sloped to the match the drain, which allows for a good deal of height adjustment.

Basement Bathroom Shower Drain Installation

Basement Bathroom Shower Drain Installation

The hole in the concrete slab floor is filled with fine foundation rock, also known as “concrete screenings”. It packs very well for a solid fill. Fill in about 3 or 4 inches, tamp and repeat.

Basement Shower Drain: Fill the Concrete Slab Hole with Foundation Rock

Basement Shower Drain: Fill the Concrete Slab Hole with Foundation Rock

The bathroom walls are painted a light blue color while there’s no worry about paint drips on the bare floor. The Wagner Paintmate roller is my favorite for painting walls. I didn’t paint the shower stall walls which were primed with white paint by the home builder because the shower walls will be covered with cement backer board and tile.

Finish a Basement Bathroom: Paint the Walls

Finish a Basement Bathroom: Paint the Walls

The shower pan and mortar bed is built in How to Finish a Basement Bathroom – Part 3.

Thanks for reading,

Bob Jackson

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10 Responses to How to Finish a Basement Bathroom – Part 2

  1. Marky Mark May 15, 2011 at 10:09 am #

    I don’t understand why there is no trap for the shower drain. What prevents the “ode of sewage” in the bathroom?

    • Bob Jackson May 15, 2011 at 10:48 am #

      The builder installed a trap, it’s in the dirt. I verified a trap was there by seeing standing water in the pipe with a flashlight; running a flexible metal snake down the drain and “feeling” two turns; and lastly I accidentally dropped a screw down the drain and was able to retrieve it from the U bend with a magnet. There’s never been any sewer gas odor nor siphoning sounds from the drain that would indicate a problem with the trap.

      Thanks for reading,
      Bob

  2. Sam December 30, 2011 at 12:08 pm #

    Thanks for ther great posts and pictures. I have a question.
    Did you fill foundation rock only or poured concrete on top of the foundation rock?

    • Bob Jackson December 30, 2011 at 1:00 pm #

      I filled the hole with foundation rock in layers, tamping it down as along the way to fill all voids. Not too hard though – don’t want to break the PVC drain pipe. The foundation rock packs really well. The mortar bed for the shower pan provided the solid cap on the foundation rock. Notice the foundation rocks stops about 1 or 2 inches below the edge of the concrete floor in the photos to create a supporting “plug”.

      Thanks for asking!

  3. James September 1, 2012 at 4:16 pm #

    I am installing a sewage basin from scratch. There is zero plumbing under the concrete to start with. I am going to bust up the concrete and build my rough in. I have everything figured out, except where to connect the vent. I assume I connect it to an existing vent. Can you help? Thank you

    • Bob Jackson September 1, 2012 at 4:47 pm #

      You are correct – the sewage basin air vent pipe must be connected to the outdoors. It’s easy enough to tap into the existing plumbing vent pipe in the attic by installing a Wye or Tee fitting, you’ll need to figure out a way to route the PVC vent pipe from the attic to the basement.

      Part 10 of the project series details the sewage basin plumbing vent pipe.

      Let me know if I didn’t fully answer your question.

  4. James September 2, 2012 at 7:59 am #

    Yes, you have answered my question. Thank you for answering so quickly. I have one more question if you dont mind. The sewage basin have no previously cut holes in the side of it. I am assuming that I have to drill my own holes or did I get the wrong basin? My basin is a Parts 2 O brand. I looks like there are extra grommets for that purpose, that come with the lid.

    • Bob Jackson September 3, 2012 at 8:52 am #

      The sewage basin should have preformed inlets on the side for sewage line entrance. If there are two or more inlets, the inlets might be capped. This provides the installer with flexibility in the plumbing configuration by cutting open or both inlets. My basin has two inlet ports, both inlets were capped with an integral plastic covers. Since my basement bathroom has only one sewage line under the concrete slab, only one inlet was cut open and fitted with a grommet to seal the sewage line.

      Your Parts2O brand sewage basin should have a factory made inlet. Take a look at this Parts2O basin and read the Technical Specifications sheet towards the bottom of the page.

      If your basin lacks factory-made inlet ports then you should consider purchasing a different sewage basin. This Little Giant package from Amazon.com is a good example: Little Giant 9S-SMPX-LG Pre-assembled Package w/ 20″ x 30″ Polyethylene Basin, 1 Piece Cover w/Bolt-

      BTW – it sounds like you’ve got a fair amount of concrete slab to cut into to install the sewage plumbing and basin. Instead of drill, hammer and chisel consider renting an electric concrete wet saw. Gas powered wet saws are fine for outdoors but would suffocate you indoors. A tool rental place should have an electric wet saw – faster, easier and nice straight cuts: http://www.youtube.com/watch?v=gUvVzZv4vJ8

  5. Mark December 21, 2014 at 10:26 pm #

    Where did you find the Foundation rock bag? I was searching Home Depot/Lowes/Menards websites could not find this product. Please advise. Thank you

    • Bob Jackson December 22, 2014 at 11:03 am #

      It’s been several years and I don’t recall where I bought the bags of Patio & Sidewalk Foundation mix mfg. by East Loop Sand Co.. I still have a bag and the label states “FOUNDATION is a mix of COURSE and FINE”. “COURSE for drainage and stability. FINE is finely ground stone to hold your brick, stone or slate more securely in place than sand or plain soil. FOUNDATION COURSE AND FINE is designed to work together for a more attractive and functional patio or sidewalk.”

      An equivalent material is “Slag Sand” and “Paver Base“.

      Slag sand and paver base is an angular sharp material with various sized grains that packs very hard, much different than plain sand which has fine round grains.

      Check the local landscape supply stores that sell brick pavers and stone.

      Thanks,
      Bob

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