Shower Pans and Bases: Tile, Acrylic, Solid Surface and Pre-Sloped Systems

The shower floor carries more water than any other surface in the house, and it is the part most likely to leak if it is built wrong. You have two broad choices: a floor built on site and finished in tile, or a ready-made base in acrylic, solid surface or enameled metal. Each has its own way of keeping water out of the framing. This page compares them so you can choose before the drain is set. The membranes themselves are explained in waterproofing explained.

The options compared

Tiled shower floors

A tiled shower floor is built in layers, and the waterproofing sits in one of two places.

Traditional mortar bed with a liner

This is what the plumbing code describes for site-built shower receptors (2021 Uniform Plumbing Code section 408.7). A sloped pre-bed goes down first, then a sheet liner of an approved material, such as PVC or CPE, turned up the walls and over the curb. A clamping drain grips the liner, with weep holes to let water that soaks through the mortar drain out. Mortar and tile go on top. The TCNA Handbook calls this a "water in, water out" shower (method B415): the tile and mortar get wet, and the liner below carries the water away.

It is a long-proven method. Its weakness is the weep holes: if mortar or debris blocks them, the bed stays saturated, which shows up as a dark grout floor and a musty smell. The code requires the weep holes to be protected from clogging.

Bonded membrane on top

In the bonded method (TCNA B421 and related methods), the mortar bed is sloped to the drain and a waterproof membrane is bonded on top of it, directly under the tile. Water stops just below the tile, so the mortar stays dry. These systems use a drain made to bond to the membrane.

Pre-sloped foam trays

Foam trays come from the factory already sloped to a center or linear drain position and are covered with the same system's membrane. They are lighter and faster than a mortar bed and give a consistent slope. They come in a range of sizes; many can be trimmed, and some systems use extension pieces. Use the tray, membrane and drain from one system, as tested together.

Ready-made bases

Acrylic and fiberglass bases are covered by the CSA B45.5/IAPMO Z124 plastic plumbing fixture standard, which includes shower bases and stalls. They are light and quick to install, have no grout and come in many standard sizes, including sizes meant to drop into a former tub space. Acrylic holds its color and gloss through the material; fiberglass is coated, so its surface wears through sooner under abrasive cleaners.

Solid surface and stone resin bases are heavier, feel more solid underfoot and often come in matte finishes. Some can be cut down to fit an odd alcove. They look closer to stone without the grout.

Enameled cast iron and steel bases are covered by ASME A112.19.1/CSA B45.2. The enamel is hard and glossy and can chip if something heavy drops on it.

Every ready-made base has to sit fully supported, usually on a mortar or setting bed, so it does not flex. A base that creaks or flexes underfoot will eventually crack or open the seal at the drain. The base flange must lap behind the wall waterproofing so water runs into the base, not behind it.

Drains and slope

The plumbing code sets the finished slope of a shower floor at no less than 1/8 inch and no more than 1/2 inch per foot toward the drain (2021 UPC section 408.5), and Washington requires a shower drain of at least 2 inches (WAC 51-56-0400). A ready-made base has its slope and drain position built in, so the drain under the floor must line up with it. A tiled floor can put the drain wherever the design wants, including a linear drain for a curbless shower. The full code list is on the bathroom plumbing code page.

Slip resistance

For tile, the industry test is ANSI A326.3, which measures wet dynamic coefficient of friction (DCOF) and sorts tile into use categories. Ask for the DCOF value and category on the spec sheet. Keep in mind the TCNA's own caution: DCOF does not predict whether a particular person will slip.

On shower floors, small mosaics with many grout joints are common because the joints add grip and the small pieces follow the slope. Large tile works on a single-plane slope to a linear drain. Ready-made bases rely on a molded or textured finish. More on tile choice is in porcelain versus ceramic tile and natural stone in bathrooms.

Who should choose which

• Choose a tiled floor if the shower is an unusual size or shape, you want a curbless entry or linear drain, or you want the floor to match the bathroom tile.
• Choose a foam tray system if you want tile with a consistent factory slope and the shower is a standard rectangle.
• Choose acrylic for a hall bath or tub-to-shower conversion where cost, speed and easy cleaning matter most.
• Choose solid surface or stone resin if you want a stone-like look with no grout and a solid feel.
• Choose enameled metal if you want a hard, glossy surface and the size you need is made.

What to check before you buy

• The exact interior size, and whether it meets Washington's minimum shower size.
• Drain position (left, center, right or linear) against where your drain is now.
• Whether the base is listed to its standard; the marking is usually on the unit or its spec sheet.
• Threshold height, if anyone in the house has trouble stepping over a curb.
• For tile: the DCOF and use category, and whether the tile is rated for wet floors.
• For a tiled floor: which waterproofing method will be used, and when the flood test happens.
• The manufacturer's installation instructions for bedding the base, since warranties often depend on them.

JDI Construction chooses the base or pan system with you during design, together with the walls and drain, so the three are built as one system. To talk it through for your own shower, start on our Vancouver shower remodeling page or see shower remodel cost for planning ranges.