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Shower Stall Shims Are Not Included: What Size to Make and How to Level the Base

Updated September 2026

▶Glossary9
  1. Making Your Own Shims
  2. Mortar Bed or Shims?
  3. Setting and Leveling the Base
  4. When the Seams Do Not Line Up
  5. Getting Help During the Install
  6. Related Guides
  7. Related Videos
  8. Common Questions
  9. Still Need Help?

Shim blocks are not included with Ella low-threshold shower stalls, including the 33 by 60 inch one-piece unit sold through home improvement retailers. You make your own. Each shim should be about 6 inches long, with the thick end 1 1/2 inches. The shims go under the base to bring it level, and the unit is then fastened to the studs as the instruction sheet describes. A mortar bed is not required for these low-threshold stalls.

Making Your Own Shims

Cut wedge-shaped shims about 6 inches long, with the thick end 1 1/2 inches and tapering toward the other end. Cut several, because the number you need depends on how far out of level the floor is. Have them ready before the unit goes into the alcove so the base can be adjusted while it is still easy to move.

Mortar Bed or Shims?

Setting the base in a mortar bed applies only to Ella's barrier-free roll-in showers. The low-threshold one-piece and three-piece stalls are leveled on wedges under the base, exactly as the instructions specify, and are not set in mortar. That also removes the worry about mortar finding its way down the drain pipe. Full step-by-step instructions for the molded-seat unit are in the three-piece low-threshold shower installation guide.

Setting and Leveling the Base

  1. Dry fit the unit in the alcove before fastening anything. This confirms the drain location, the fit against the studs and the alignment of the pieces while adjustments are still easy.
  2. Check the floor with a level and the walls with a level or plumb line. The base must be level and the walls must be plumb, and both should be corrected before the unit goes in.
  3. Set the base in place and slide shims into any gaps beneath it. Check level front to back and side to side, and adjust the shims until the bubble is centered in both directions.
  4. Fasten the unit to the studs as the instruction sheet describes, then recheck level after the last screw.
  5. On three-piece units, set the wall panels only after the base is level and fastened, and confirm the seams are even top to bottom before securing them.

When the Seams Do Not Line Up

On a three-piece unit, a vertical seam that is narrow at the top and wide at the bottom, paired with a horizontal seam that is wide at the bottom and narrow toward the front corner, is a tipping effect. In most cases the stud wall is pushing the upper corner of a panel. Check the base for level first, then check each wall for plumb, and correct the wall so it no longer pushes on the panel corner. More on this in what to do when the shower stall wall is out of square or the base is damaged.

Getting Help During the Install

Ella does not perform installations, but free technical support is available to whoever is doing the work. Your installer is welcome to call (800) 480-6850 directly with the unit in front of them. Having the model number and a couple of photos of the alcove ready makes that call short.

Chapters in this video
  1. 0:00 Introduction to Low-Threshold Shower Installation This video provides visual guidance for installing a low-threshold 3-piece shower, emphasizing the importance of referring to the installation manual.
  2. 0:24 Dry Assembly and Pre-Installation Checks The installer dry assembles the modular shower to ensure correct panels, drain location, and proper alignment before moving it into the bathroom space.
  3. 1:54 Preparing the Framing Pocket and Subfloor The installer checks the framing pocket for proper sizing, square, plumb, and level, making necessary adjustments and inspecting the subfloor for integrity.
  4. 4:07 Installing the Drain Body and Base Support The installer installs the drain body, prepares the drain to meet local plumbing codes, and applies silicone adhesive for proper support and adhesion of the base.
  5. 5:53 Permanently Installing and Securing the Base The installer permanently positions and levels the shower base, securing it to all available studs and cutting the drain pipe even with the rubber gasket.
  6. 7:22 Installing the Wall Panels and Valve The installer installs the wall panels using a pin and slot system, then installs the valve, connecting the hot and cold water supply lines.
  7. 10:19 Finishing Touches and Accessories The installer caulks all seams, recommends client involvement for accessory placement, and suggests an optional flange trim molding kit for a seamless transition.

Common Questions

Why did my shower stall not come with shims?
Shims are not part of the shower package. Floors vary too much for a fixed set to be useful, so the installer cuts shims to suit the site. Ella's recommended size is about 6 inches long with a 1 1/2 inch thick end.
Do I need to set the shower base in mortar?
No. A mortar bed applies only to the barrier-free roll-in showers. The low-threshold one-piece and three-piece stalls are leveled with wedges under the base and then fastened to the studs.
Should the base be perfectly level or tilted toward the drain?
The base must be level, as the instruction sheet specifies. Use wedges under the base until it reads level front to back and side to side. A base that rocks or sits high on one corner will throw off the wall panels later.
Why do the wall panel seams not match up?
Uneven seams usually trace back to a stud wall pushing on a panel's upper corner and tipping it. Check the base for level first, then check each wall for plumb. Correcting the wall brings the seams back into line.
Can Ella send someone to install my shower stall?
No. Ella supports your installer with instructions and free technical support by phone, and a licensed local contractor does the work. Dry fitting the unit and checking the walls and floor before the install prevents most problems.

Still Need Help?

Open a ticket at ellasbubbles.com/support or call (800) 480-6850 and have your model and serial number ready.

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