Why Is Grout Cracking Around My Shower Drain?

Grout cracks around a shower drain when the drain has failed, not the grout: the drain flange or grate is not fully supported and moves underfoot, water is trapped in the mortar bed because the weep holes are blocked or the bed under the liner was never sloped, the drain sits too high or too low, or the tile was cut back so far that a wide ring of grout does a tile's job. Which one depends on your drain type, and each has a test to run before you regrout.

Why the drain, and which drain you have

The drain is the lowest, wettest point of the floor and a separate part set into mortar, so its grout ring shows any drain fault first. Generic causes such as shrinkage and deflection are covered in the crack pattern guide. Cracks confined to the tiles around the drain trace back to one of five drain faults, and regrouting without finding which one is how people end up with grout that keeps cracking.

The NTCA describes two basic shower builds: a "Water In, Water Out" system with "a clamping ring drain and waterproof shower pan liner," and a "Sealed System" with "a bonding flange drain and a waterproofing membrane." Lift the grate to tell them apart.

• Clamping-ring drain over a mortar bed. A strainer screwed into a threaded barrel. Below the tile, a clamping ring bolts the pan liner to the drain base, and weep holes at liner level drain the water that soaks through the grout and mortar. Oatey's tile shower drain is one example.
• Bonded-flange drain. A membrane directly under the thinset is bonded to a wide flange at the top of the drain, as on Schluter KERDI-DRAIN, so little water is held under the tile.
• Linear drain. A channel along a wall or at the entry, with the floor in one plane. Schluter KERDI-LINE also has a bonding flange.

Cause, test and fix by drain type

No manufacturer or trade group puts these together. The table combines the Schluter drain data sheet, the NTCA leak guide and Oatey's clamping-ring drain instructions with the tests a setter runs on site.

A ring that is both wet and loose usually means a saturated bed that has lost its bond: treat it as the wet cause.

Cause 1: the flange or grate is not fully supported

Schluter spells this out. For KERDI-DRAIN: "Place a ring of loose mortar up to the inlet hole in the floor and firmly press the drain into the mortar. The bonding flange must be fully supported to prevent damage to the tile assembly (e.g., cracked grout around drain)." In concrete floors it limits the hole around the waste line to 5 inches (125 mm), because "a larger hole can lead to lack of support and damage the tile assembly (e.g., cracked grout around drain)." Over wood, it calls for at least 1 inch (25 mm) of mortar at the flange perimeter.

The grate needs support too: fill the step in the bonding flange with unmodified thinset and "back-butter the underside of the grate to ensure full support." A KERDI-LINE channel must be embedded "ensuring full support of the bonding flange." A clamping-ring drain fails the same way when the barrel is not packed solid in the mortar bed and flexes the grout ring on its threads.

Test and fix: tap every tile within a foot of the drain and listen for a hollow note, then stand on the grate while someone watches the ring under a low flashlight. A click or fresh grout dust means movement, and regrouting alone will crack again. Lift the tiles and grate, pack the void, back-butter and reset the grate flush, and reset the tiles with full coverage. On a bonded system, a membrane damaged at the flange is repaired to the drain maker's details first.

Cause 2: clogged weep holes and a saturated bed

A clamping-ring shower is designed to get wet under the tile: water runs down to the liner and out through the weep holes. Oatey's drain instructions protect those holes twice: "Make sure the weep holes are clear of any residual pan liner material or silicone sealant," and "before the final mortar application place some pea gravel over the weep holes so the mortar does not completely cover them."

Skip the gravel or smear thinset into the holes and the bed cannot drain. The NTCA lists "Blocked weep holes at drain" first among causes of cracking grout or mineral buildup at grout lines. Grout over a permanently wet bed weakens and fails first where the bed is wettest: at the drain. The white crust is efflorescence, and the sour smell is covered in smelly grout.

Test and fix: keep the shower out of use for three days or more with the fan running, as described in grout that stays wet or dark. Grout that stays darkest at the drain points to the weeps. A plumber can sometimes reach them by unscrewing the barrel; often the tile and bed around the drain come out, the holes are cleared, gravel is packed around them and that section is rebuilt.

Cause 3: no preslope under the liner, or a damaged liner

Weep holes only work if water on the liner runs to them. Oatey: "Code requires a sloped base under waterproof layer," sloped "up and away from the top of but not over the drain base to all outside vertical framing 1/4" per foot." Its pan liner instructions add that the sloped bed "should be flush with the top surface of the drain base." A liner laid flat holds a puddle, and the bed above never dries. The NTCA lists an unsloped floor under the liner as a cause of shower odor, and a liner breach as a cause of cracking grout.

Test and fix: the dry-out test shows water held under the tile but cannot tell a flat liner from clogged weeps. That takes opening the floor at the drain or a pan test; Oatey's own flood test fills the pan to just below the curb for at least 4 hours. There is no surface fix: the floor comes out to the subfloor and is rebuilt. The NTCA warns that grout, caulk or sealer repairs on a leaking shower "will, at best, provide only a temporary fix," the decision covered in when regrouting won't work.

Cause 4: the drain is set too high or too low

Below the tile, the NTCA lists a drain body "incorrectly installed higher than the surrounding floor" that "will not drain" among causes of odor; the bed then holds water as in cause 2. At the surface, Oatey threads the barrel into the clamping ring "so the finished floor will be flush with the top of the drain barrel," and notes that inverting the ring raises the finished height by about 3/4 inch. Schluter's grate assembly adjusts for tile thickness and tilt and is pressed "flush with the tile surface."

A grate left proud holds a ring of water around it. A grate set low leaves the last tiles bent down to it on patchy thinset, and they rock and crack the grout.

Test and fix: lay a straightedge across the grate in two directions; it should meet grate and tile at the same height, with the tile still falling toward the drain. An adjustable grate that is slightly off can be reset with the first ring of tile. A drain base at the wrong height means rebuilding the floor around it.

Cause 5: tile cut too small at the drain

Cutting tile back from a round grate and filling the gap with grout is a common shortcut. The ring that results is far wider than the field joints and thin where it sits over the flange, so it shrinks, cracks down the middle and pulls away from the metal. The shower floor grout guide gives the rule: finish the tile just short of the grate with a joint about the width of the field joints. Schluter's tileable cover sets the tile flush with all sides of the covering support.

Test and fix: measure the ring at its widest and compare it with the maximum joint width on the grout's data sheet (often 1/2 inch for sanded grout; see wide grout joints). Replace the cut tiles with pieces that reach a normal joint. Where tile meets a metal grate or channel, a flexible sealant usually outlasts grout, for the reasons in caulk vs grout for movement joints.

When the drain is not the answer

• Cracks well beyond the drain. If cracks also cross the floor, run along the walls or reach the bathroom, look for floor deflection and missing movement joints instead (see why grout cracks).
• Water below the shower. Ceiling stains below, or damp floor or walls outside, mean water is escaping. The NTCA's first step is a plumber checking the valve, supply lines and "Drain and trap," then a pan test, before anyone touches the grout.
• A new shower. Fine cracks in grout a few weeks old may be shrinkage; see grout cracking after installation.

Repair order

1. Lift the grate and identify the drain type.
2. Run the dry-out test. A ring that stays wet points to causes 2 to 4; a dry ring to causes 1 and 5.
3. Tap, load and straightedge the drain area.
4. Fix the cause, then rake the joints to depth and follow regrouting a shower. Epoxy grout absorbs far less water than cement grout at the drain.