Building a tile shower on a mud bed with a PVC pan liner.

Liner Rules (IRC P2709 / UPC 408.7 / TCNA B415):

1. Material: Minimum 40-mil PVC (ASTM D4551) or CPE. No 30-mil "shower pan liners" sold for other uses.
2. Slope: Liner must be installed over a pre-slope (min ¼"/ft) sloped to the drain. Flat liners hold water and rot.
3. Height: Extend minimum 3" above curb top (IRC P2709.2) and 6" up walls (TCNA) behind backer board.
4. Corners: Use pre-formed corner dams or fold/cut/glue per manufacturer. No raw folds at dams. Solvent weld all seams (PVC cement).
5. Drain Connection: Clamp liner between drain body clamping ring and flange. Use manufacturer’s sealant/gasket. No screws through liner. Weep holes in clamping ring must stay open (protect with gravel/keepers).
6. Curb: Liner runs continuous over curb top. No seams on curb top. Fasten liner only at outer curb edge (staples/nails above curb line). Never penetrate liner on top or inside face.
7. Penetrations: Seal valve/shower arm penetrations with boot/flange kits solvent-welded to liner. Silicone is not a primary seal.
8. Protection: Cover liner immediately with mortar bed. Protect from trades/damage.

Flood Test (Mandatory - IRC P2709.3 / UPC 408.7.2):

1. Plug drain below weep holes (test plug in pipe or inflatable).
2. Fill to curb top (or 2" min above threshold).
3. Mark water level. Wait 24 hours (IRC) / 15 min (UPC min, 24 hrs best practice).
4. Pass: No level drop. Fail: Any drop = find leak, repair, retest.
5. Document with photos/time-stamps for inspector.

Critical: Do not install tile/mud bed over untested liner. If curb is concrete block, liner must wrap over top; do not embed curb in liner.

When installing a PVC pan liner in a tile shower over a mud bed, follow these key rules and testing procedures per the International Plumbing Code (IPC) Section 417.5 and TCNA Handbook guidelines:

Liner Rules:

1. Material & Thickness: Use minimum 40-mil PVC sheet (ASTM D4551). Thinner liners are not code-compliant for shower receptors.
2. Slope: The subfloor (mud bed) must slope 1/4 inch per foot toward the drain to ensure drainage. The liner itself must be installed flat and smooth over this slope.
3. Extension Up Walls: The liner must extend at least 2 inches above the finished curb height and 6 inches up the walls (measured vertically from the top of the curb). At corners and seams, it must go at least 8 inches up to prevent wicking.
4. Seams & Joints: All seams must be heat-welded or solvent-welded using PVC-specific cement. Mechanical fasteners (staples, nails) are prohibited in the flooded area (within 8" of the curb and drain).
5. Drain Connection: Use a two-piece clamping drain designed for PVC liners. The liner must be clamped between the drain body and the clamping ring, with weep holes open to allow moisture to escape into the drain.
6. Protection: Cover the liner with a separation layer (e.g., 15-lb felt or synthetic underlayment) before applying the finish mud bed to prevent damage from trowels or debris.

Testing the Liner (Flood Test):

Per IPC 417.5.2, the liner must be tested before installing the finish mud bed and tile:

1. Seal the drain opening with a test plug.
2. Flood the shower pan with water to a depth of 2 inches above the curb.
3. Hold the water for at least 15 minutes (some jurisdictions require 30 minutes).
4. Inspect the entire liner surface, especially seams, corners, and drain area, for leaks.
5. No leaks permitted. If any are found, repair and retest.

> ⚠️ Critical: Never install tile or finish mud bed over an untested liner. Leaks hidden beneath tile can cause structural damage and mold. If unsure, consult a licensed plumber — improper liner installation is a common cause of shower failures. Always verify local amendments to the IPC.