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How to Install a Fiberglass Base Over Concrete

Plumb the drain using a special leak-proof drain assembly

how to install a shower stall,Family Handyman
Install a fiberglass shower stall over a concrete floor using a special drain assembly that eliminates leaks. You run the drain line under the concrete.

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Step 1.Shower Drain Installation: Run a drainpipe under the concrete floor

shower drain installation

Shower stall on concrete

A shower usually requires a 2-in. drain, with the P-trap located under the concrete slab.

If you want to install a shower over a concrete floor, a fiberglass shower stall will work just fine. Ideally, youll already have a drain roughed in, with the pipe sticking a few inches above the floor. Otherwise you have to break through the concrete to run a new line for a shower stall installation.

If you have a pipe stubbed up, call the plumber or contractor who did the work to confirm it. The 2-in. pipe is typically the shower or tub drain. Line it up exactly with the drain hole in the bottom of your shower bay. This position determines the location of the stud walls around the shower. The supplier may be able to provide a dimensioned drawing of the shower bay, so you dont actually have to put it in first.

If the existing 2-in. drainpipe isnt where you want it, youll have to break up the concrete and replumb the drain.

Make sure the drainpipe extends at least an inch above the concrete. If the pipe is too short, you’ll have to break up the concrete and extend it. Also, youll need at least a 1-1/2-in. space between the pipe and the concrete to accommodate the drain assembly (see photo below). If there isn’t, carefully chisel out the concrete around the pipe.

Tip: If youre considering a single-piece shower bay, make sure you can get it into the new bathroom space. You may have to bring the unit into the space before framing the doorway or walls. If access is a problem, check out multiple-piece units that will fit through doorways more easily.

Step 2. Shower Drain Installation:Mount the leakproof drain assembly

shower drain installation

Drain assembly close-up

The assembly locks tightly to the pipe and clamps to the edge of the shower base to make leakproof seals.

After you frame the shower walls to fit the shower bay, lay the bay on its back and install the shower drain. Use a special leakproof shower drain assembly called the No-Caulk Shower Drain. Its available at home centers and plumbing supply houses. Although these drain baskets are available in plastic, I’d opt for the brass one. Follow these steps to attach the shower to the drain:

  • Roll out a coil (about the diameter of a pencil) of plumbers putty (available at all hardware stores) and wrap it under the drain basket flange.
  • Hold the shower drain basket in position in the shower bay drain hole, slide on the washers, and then thread on and hand-tighten the exterior setting ring. Tighten the ring with a large slip-joint pliers until its firmly in place. You shouldn’t be able to move the shower basket by hand. The plumbers putty will squeeze out.
  • Lower the shower bay and basket assembly over the drainpipe. Mark the pipe about 3/4 in. below the drain basket flange.
  • Lift the shower bay out of the way and cut the drainpipe to length. A hacksaw works well. Make sure to cut the pipe square, not angled.
  • Set the shower bay and basket assembly back over the pipe. Slide the caulking gasket over the pipe and push it all the way down so it sits against the lip at the bottom of the drain basket. You may have to tap this gasket into place with a hammer and a thin piece of wood.
  • Thread on the caulking nut and firmly tighten to compress the caulking gasket and seal the pipe. Use the slotted bar tool that comes with the drain assembly. Stick the flat blade of a screwdriver into the bars slot and firmly hand-tighten.
  • Snap on the perforated drain cover (not shown).

Required Tools for this Project

Have the necessary tools for this DIY shower drain installation project lined up before you startyou’ll save time and frustration.

  • Hacksaw
  • Hammer
  • Slip joint pliers
Flat-blade screwdriver

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time for a shower stall installation. Here’s a list.

  • Drain assembly
  • Plumber's putty

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