Grout for Bathrooms: Cement, Urethane and Epoxy

Grout is a small part of a bathroom's tile budget and a large part of how the bathroom ages. It is where mildew shows up, where stains settle and where cracks appear if something moves. In a shower, it is also the part people most often assume is keeping the water out, which it is not. This page covers the grout types for bathrooms, joint widths, sealing, mildew, color and the joints that should not be grouted at all.

Grout is not waterproof

Start here, because it shapes every other decision. Cement grout is porous. The Tile Council of North America (TCNA) puts it plainly in its steam room guidance: glazed tile is vapor impermeable, but the grout is not. Water and vapor pass through cement grout into whatever is behind it.

That is fine when the layer behind the tile is a waterproof membrane or board system, as it should be in every shower. It is a problem in older showers built with tile over ordinary drywall or with a failed membrane. Grout's job is to fill joints, lock tile edges and keep the surface cleanable. Waterproofing is a separate layer, explained in waterproofing explained.

Grout types compared

Tile grouts are made to American National Standards listed by TCNA. The standard a product meets is on its data sheet, and it says more than the marketing name.

A118.6 and A118.7 set performance criteria for cement grout, including shrinkage, water absorption and strength. "Urethane grout" is a type rather than a standard: no ANSI standard was found that names it, so judge a urethane product by its data sheet and whether it claims A118.19.

TCNA advises specifying ACT grouts installer certification on every job where cement or epoxy grout is used. It is a reasonable question to ask any tile setter.

Which grout where

• Shower walls: high-performance cement or pre-mixed grout is a good balance. Epoxy if you want the least maintenance.
• Shower floors: the hardest-working grout in the house. Epoxy or a high-performance cement grout sealed and kept up.
• Bathroom floors: high-performance cement or pre-mixed. Lighter grout colors show traffic soil on floors faster.
• Steam showers: follow the waterproofing system maker; see steam showers.
• Natural stone and handmade tile: test first. Pigment can stain porous stone and exposed clay, and epoxy can be hard to clean off textured surfaces. See natural stone and handmade tile.

Joint width

Joint width comes from the tile, not from taste alone. Rectified tile, with ground edges, can take narrower joints than calibrated tile. For tile with any side over 15 inches in running bond, ANSI A108.02 sets an average joint of at least 1/8 inch for rectified tile and at least 3/16 inch for calibrated tile, increased by the amount of edge warpage. Tile makers often state a recommended joint on the box.

Sanded cement grout is for wider joints and unsanded for narrow ones; each grout's data sheet gives the joint range it is made for. Using the wrong one leads to shrinkage cracks in wide joints or a grainy fill in narrow ones.

Sealing

Cement grout is usually sealed after it has cured for the time its maker states. Sealer reduces stains and water uptake at the surface. It wears, especially on shower floors, so it needs renewing on the sealer maker's schedule. A simple check: if drops of water darken the grout quickly, the sealer has worn.

Epoxy grout is not sealed. Most pre-mixed grouts do not need sealing either, but check the product. Sealing over the wrong grout type can leave a film.

Mildew, moisture and the Northwest

Mildew on grout is a moisture problem first. The EPA's guidance is direct: the key to mold control is moisture control. It advises keeping indoor humidity below 60 percent, ideally 30 to 50 percent, and running the bathroom fan when showering. HVI, the ventilation industry's certification body, recommends leaving the fan on for 20 minutes after using the bathroom.

For cleaning, mild detergent and warm water handle most surface mildew. Washington's Department of Health recommends washing with a mild detergent solution, and this guide does not recommend bleach. Avoid acidic cleaners on cement grout and stone; they wear grout down over time.

Color choice

Grout color changes the whole surface. A grout matched to the tile makes the wall read as one plane and hides small irregularities. A contrasting grout outlines every tile and makes the pattern the feature. Mid-tone grays and warm neutrals hide floor soil well. Very white grout on a floor shows every footprint; very dark grout in a shower can show mineral film from drying water. Pairings by tile color are on tile and grout color pairings.

Always look at grout cured on the actual tile, not on a color stick. Cement grout dries lighter than it looks wet, and its final color depends on mixing and cleanup.

Where not to use grout

Inside corners, the joint between wall tile and the tub or shower pan, and the joint where tile meets a different material all move slightly as the house and fixtures expand, settle and get loaded with water. Grout there cracks. Those joints get a flexible sealant made for tile, color-matched to the grout. Expect to renew sealant joints as part of normal upkeep.

Who should choose which

• Standard cement grout: budget projects, easy future repairs, and owners happy to seal.
• High-performance cement grout: most bathrooms; a sensible default.
• Pre-mixed or urethane: owners who want consistent color and no sealing, with an installer who knows the product's cure times.
• Epoxy: shower floors, low-maintenance households and stain-prone areas, with an experienced setter.

The kitchen guide's grout guide covers the same products from the kitchen side, including backsplash grout. At JDI, grout type and color are chosen with the tile during design, and test boards are made for stone and handmade tile. See how we approach a bathroom remodel in Vancouver.