Hot mop vs. PVC liners, Kerdi and liquid membranes

An honest comparison of the common ways to waterproof a shower pan: how each one works, where it shines and what it asks of the installer.

The short answer

All four methods can make a watertight shower when they're installed correctly and tested. Hot mop's strengths are a seamless membrane built to the exact shape of the shower and a long track record in Southern California. Sheet liners are common and simple; bonded sheet and liquid membranes keep water closer to the tile. The best choice depends on the shower design, the drain, your tile setter and what your inspector expects.

Two families of shower pans

It helps to know there are two basic designs:

• Membrane under the mortar bed. The waterproof layer sits below a thick mortar bed. Water that soaks through the tile and mortar reaches the membrane and drains out through weep holes in a clamping-ring drain. Hot mop and PVC/CPE liners work this way.
• Membrane bonded under the tile. The waterproof layer is applied on top of the sloped mortar bed or board, right under the tile, with a drain made to bond to it. Water stops just below the tile. Bonded sheet membranes such as Schluter-Kerdi and liquid-applied membranes work this way.

Hot mop

Layers of felt paper bonded with hot-applied asphalt, mopped over the pan, up the walls and over the curb, and clamped into the drain. It's built in place by a specialty crew, then flood tested.

• Strengths: one seamless piece with no folded corners; molds to any shape, including benches, niches and tub decks; a long-established method in Southern California that builders, tile setters and inspectors know well.
• Trade-offs: needs a hot mop crew and equipment; the asphalt smells while it's applied; like any under-mortar pan, it depends on a properly set drain with clear weep holes.

PVC and CPE sheet liners

A flexible plastic sheet laid into the pan, folded at the corners, run up the walls and over the curb, and clamped into the drain, with a mortar bed on top.

• Strengths: widely available; installed by many tile setters; no hot equipment.
• Trade-offs: corners are folded and the curb usually needs pre-formed corners or patches; seams must be solvent-welded or glued correctly; odd shapes take more cutting and joining.

Bonded sheet membranes (such as Schluter-Kerdi)

A thin sheet membrane set in thin-set mortar on top of the sloped mortar bed or board, with overlapped seams and a drain made to bond to it. The tile is set directly on the membrane.

• Strengths: keeps water just below the tile, so the mortar bed stays dry; a full system with matching corners, drains and niches.
• Trade-offs: relies on using that system's parts and following the maker's instructions closely; seams and corners are lapped by hand; needs the matching drain.

Liquid-applied membranes

A waterproofing liquid rolled, brushed or troweled onto the prepared surfaces, usually in more than one coat, sometimes with fabric at corners and changes of plane.

• Strengths: seamless when applied evenly; easy around pipes, corners and custom shapes; bonds directly under the tile.
• Trade-offs: performance depends on reaching the maker's required thickness everywhere, which is hard to see once it's dry; needs a compatible drain.

Side by side

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Swipe to compare all methods →

	Hot mop	PVC / CPE liner	Bonded sheet (e.g. Kerdi)	Liquid-applied
Where it sits	Under the mortar bed	Under the mortar bed	Right under the tile	Right under the tile
Seams & corners	None: built as one piece	Folded corners; welded or glued seams	Lapped seams; preformed corners	Seamless if applied evenly
Custom shapes	Excellent	Harder	Good, with system parts	Good
Drain	Clamping-ring drain with weep holes	Clamping-ring drain with weep holes	Bonding-flange drain for that system	Drain compatible with the product
Who installs	Specialty hot mop crew	Tile setter or contractor	Tile setter, to the system's instructions	Tile setter, to the maker's thickness
Testing	Flood test before mortar and tile	Flood test before mortar and tile	Flood test per the system's instructions	Flood test once fully cured

Product details change and every manufacturer has its own instructions. Follow the maker's current requirements and confirm local requirements with your building department.

Which one should you choose?

Hot mop is a strong fit when you want a traditional mortar-bed shower, when the shower has a custom shape (benches, niches, angled walls, tub decks), or when your tile setter and builder prefer it. A bonded system can make sense when the tile setter is committed to that system from the floor to the walls. What matters most is that whichever method you pick is installed carefully, matched to the right drain and flood tested before tile.

Not sure? Call (949) 446-4413. We'll tell you honestly whether hot mop is the right fit for your shower.

Comparison questions

Is hot mop better than a PVC shower liner?

Both sit under the mortar bed and use the same kind of drain. Hot mop's advantage is that it's built in one seamless piece, so there are no folded corners or glued seams, and it fits custom shapes easily.

Is hot mop better than Kerdi?

They're different designs. Hot mop sits under the mortar bed; Kerdi is bonded under the tile with its own drain. Both work when installed correctly. The best choice depends on the shower, the drain and your tile setter.

Is hot mop still used?

Yes. Hot mop remains a common, well-known way to waterproof shower pans in Southern California, for new homes and remodels alike.

Can hot mop be combined with other waterproofing?

The hot mop pan handles the floor, curb and lower walls. The walls above are waterproofed with whatever wall system your tile setter or contractor uses, and the two are lapped together as part of the shower design.

Get your shower pan done right.

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