Grout vs Caulk: Which Goes Where in Tile Work?
Grout vs caulk explained: grout for the joints between tiles, flexible sealant for corners, tub edges and changes of plane — with shower specifics.
By the GableMath team · Published · 4 min read
Grout goes in the joints between tiles on a flat surface. Caulk — properly, a flexible sealant such as 100% silicone — goes wherever two planes meet or tile meets something else: inside corners, where wall tile meets the tub or shower pan, around the perimeter of a floor, and around fixtures. Grout those places and they will crack.
- Joints between tiles on one surface
- Grout (sanded or unsanded)
- Shower inside corners, tub-to-tile joint
- Silicone sealant
- Floor tile meeting walls and cabinets
- Sealant, hidden under trim if possible
- Around a toilet base
- Silicone caulk
Short answer: grout fills the joints between tiles; flexible sealant fills the joints where tile changes direction or meets something else. That's not a style preference — it's how the tile industry designs installations to survive movement. Buildings move with temperature, humidity and settling, and the joints where two surfaces meet move the most. Rigid grout there cracks; a flexible sealant stretches.
Grout vs caulk at a glance
| Grout | Caulk / sealant | |
|---|---|---|
| What it is | Cement, epoxy or urethane joint filler | Flexible sealant — silicone, urethane or polysulfide |
| Where it goes | Joints between tiles on one flat surface | Inside corners, tub and pan edges, floor perimeters, around fixtures |
| Moves with the building | No — rigid | Yes — designed to flex |
| Joint width | About 1/16–1/2 in, by grout type | At least 1/8 in at movement joints |
| Lifespan | Decades if kept intact | Several years; replace when it peels or mildews |
| Looks | Matches the tile layout | Color-matched sanded caulks mimic grout |
Grout vs caulk in a shower
Showers are where the choice matters most. The Tile Council of North America's movement-joint method, EJ171, calls for a movement joint at every inside corner — every change of plane — and around the perimeter wherever tile meets a restraining or different surface. In a tub-shower that means:
- the vertical inside corners of the walls,
- the joint where the wall tile meets the tub or the shower pan,
- the joint where the walls meet a tiled shower floor,
- and around valves, spouts and niches where the tile meets another material.
The installation standard (ANSI A108.02) says those joints must be kept free of thinset and grout, and filled with a sealant — the industry points to ASTM C920 sealants such as silicone or urethane. Plenty of installers still grout shower corners and get away with it for a while; the tile industry's own articles show what happens next — a hairline crack that lets water behind the tile.
How to do it right: keep the corner joints clean as you grout, let the grout cure, then run a bead of 100% silicone (or a color-matched sanded caulk) and tool it smooth. Where a joint is deep, a foam backer rod underneath keeps the sealant from sticking on three sides so it can stretch.
When to use grout
Grout is the right choice for every joint within a single plane: across the floor, up the wall, around the field of a backsplash. It locks the tiles together, keeps debris out of the joints and gives the finished look.
- Sanded grout for joints about 1/8 in and wider — CUSTOM's Polyblend Plus sanded grout is rated for 1/8–1/2 in joints.
- Unsanded grout for narrower joints and for glass, polished marble or other tile that sand would scratch.
- Epoxy or premixed grouts for showers and kitchens where stain resistance matters; many don't need sealing.
Our grout calculator works out bags or pails from your tile size, joint width and depth.
When to use caulk (sealant)
Use a flexible sealant anywhere movement is expected:
- Changes of plane — every inside corner on walls, and where walls meet floors.
- Dissimilar materials — tile meeting a tub, shower pan, countertop, cabinet, window or door frame.
- Floor perimeters — around the edges of a tiled floor, usually hidden under baseboard or shoe molding.
- Large floors — field movement joints in big or sunny rooms, which the tile industry also specifies.
- Fixtures — around a toilet base and where a sink or tub spout meets the wall.
Pick 100% silicone in wet areas (it's the most water- and mildew-resistant), or a tile-specific sanded siliconized caulk to match grout color. Plan to cut out and replace sealant every few years in a shower; it's maintenance, not a defect.
Which sealant to buy
| Sealant | Best for | Notes |
|---|---|---|
| 100% silicone | Shower and tub corners, tub-to-tile joint, around fixtures | Most water- and mildew-resistant; can't be painted; won't stick to old silicone |
| Siliconized acrylic latex | Dry areas, trim, paintable joints | Easier to tool and clean up; less durable in showers |
| Sanded tile caulk (color-matched) | Corners where you want a grout look | Made to match a grout line's color and texture |
| Urethane / hybrid sealants | Floor movement joints, exterior tile | Tougher and more abrasion-resistant |
How to replace failed shower caulk
- Cut and pull out all the old sealant with a utility knife and a plastic scraper. New silicone won't bond to old silicone.
- Clean the joint with a mildew remover, rinse, then wipe with rubbing alcohol so no soap film remains.
- Let it dry completely — overnight, with the fan on.
- Tape both sides of the joint with painter's tape for a straight line, run a continuous bead, and tool it with a wet finger or tooling stick.
- Pull the tape right away and let the sealant cure for the time on the tube before showering — often 24 hours.
If the grout next to the corner is cracked too, regrout that section first, then seal the corner.
Our recommendation
Grout the field, seal the corners and edges, and do them in that order. If you're tiling yourself, the tile calculator and thinset calculator size the rest of the job, and in a shower, set the tile on proper backer — the backer board calculator counts the sheets. If you're hiring it out, ask the installer whether corners will be grouted or sealed; the right answer is sealed.
Questions people ask
Should I caulk or grout first?
Grout first. Grout every joint except the movement joints at corners and edges, keep those clean of grout, let the grout cure as the bag directs, then apply sealant. The tile industry's installation standard says sealant goes in after the tilework and grout are dry.
Grout vs caulk in a shower — which goes in the corners?
Flexible sealant. The tile industry's movement-joint method (TCNA EJ171) calls for a sealant-filled joint at every inside corner and where tile meets a tub, shower pan or other material. Grout in those corners is rigid and cracks as the walls move; silicone flexes. Use a color-matched sanded caulk if you want it to look like the grout.
What is grout?
A cement-based (or epoxy or urethane) material packed into the joints between tiles. Sanded grout is for joints about 1/8 in and wider — CUSTOM rates Polyblend Plus sanded grout for 1/8–1/2 in joints — and unsanded grout is for narrower joints and easily scratched tile.
Should a toilet be caulked or grouted?
Caulked, with a flexible sealant — not grouted. Many plumbers leave a small gap at the back so any future leak shows instead of rotting the subfloor.
Why do some contractors not seal grout?
Some modern grouts — epoxy and many premixed urethane or polymer grouts — are made to resist stains without a sealer, so sealing them is unnecessary. Standard cement grout benefits from a penetrating sealer once it has cured.
Where these numbers come from
- Tile Council of North America (via IMI) — EJ171 movement joint detailing — Movement joints at all inside corners (changes of plane) and perimeters where tile meets restraining or dissimilar surfaces · checked October 2026
- Floor Trends — Tile tip: movement accommodation joints — ANSI A108.02: movement joints kept free of setting materials and grout; ASTM C920 sealants · checked October 2026
- CUSTOM Building Products — Polyblend Plus sanded grout technical data sheet — Joint width 1/8–1/2 in; coverage by tile size and joint · checked October 2026