How to Tile Around a Bathtub, Start to Finish (Backer Board, Waterproofing, and the Caulk Joint Everyone Skips)

A tub surround fails in one of two places, almost always. Either the wall behind the tile was never properly waterproofed, or the joint where the tile meets the tub was grouted instead of caulked. Everything else, the cutting, the spacing, the grout lines, is the part homeowners already picture when they think about this job. Get those two easy-to-skip steps right and the rest is straightforward work with a few real gotchas along the way.

What You Need Before You Start

Backer board, waterproofing membrane, thinset mortar, tile, spacers, grout, caulk that matches the grout colour: that’s the full material list for a standard tub surround. Cement board around three feet deep by five feet wide covers most tubs, so figure four sheets of half-inch backer board for a typical installation. Buy the thinset in white or grey depending on the tile and grout colour, nothing specialty needed for most porcelain or ceramic. On tools, a wet saw handles straight cuts, a tile nipper takes care of the fiddly bits around the spout and valve, and a notch trowel spreads the thinset evenly across the wall.

One thing worth doing before any of it: measure the surround and add ten percent for waste and cuts, not five. Bathtub surrounds involve more corner cuts and fixture cutouts than a flat wall, and running short mid-project on a special-order tile means a delay measured in weeks, not days.

Is the Bathtub Installed Before Tiling?

Yes, the tub goes in first. It has to be set, levelled across the back and sides, and anchored to the studs before backer board or tile touches the wall. The plumbing rough-in for the spout, valve, and shower arm all needs to land in the correct spot relative to the finished wall thickness too, which means the tub, the backer board, and the tile all get planned together before anyone mixes a bag of thinset.

Check the tub flange while it’s still accessible. Most tubs have a lip around a quarter inch thick running along the top edge where it meets the wall, and that flange sits proud of the stud face. Left alone, it pushes the backer board out of plane at the bottom of the wall. Furring strips, thin strips of wood run the height of the studs from the top of the flange up, solve this, and they’re a five-minute fix that a lot of DIY tub surrounds skip entirely.

Waterproofing the Wall Behind the Tile

Tile and grout are not waterproof on their own. They’re a wear layer sitting on top of a system that actually keeps water out of the wall cavity, and that system is the membrane, not the tile face. A liquid-applied waterproofing membrane rolled or brushed over the backer board seams and the whole tiled area does that job. Some installers still use 15-pound roofing felt as a vapour barrier behind the backer board on top of that, layered shingle-style so each course overlaps the one below by at least four inches, tucked tight into every corner.

Skipping or rushing this step is the single most common reason a tub surround leaks into the wall two or three years after it looked finished. Seams at the backer board joints get taped with alkali-resistant mesh tape before the membrane goes on, and every inside corner gets the same treatment. A membrane with a gap in it doesn’t show up as a problem on day one. It shows up as a stain on the ceiling below, or soft drywall on the other side of the wall, well after the warranty conversation has already happened.

Installing Backer Board Around the Tub

Cut the backer board panels to fit, holding them about a quarter inch above the top of the tub flange rather than resting directly on it. That small gap keeps the board from wicking water straight up off the tub lip. Leave roughly an eighth of an inch between panels too, since backer board isn’t meant to butt tight against itself any more than tile is.

Screw the panels to the studs with backer-board-specific screws spaced about six inches apart along the studs, deep enough to bite the wood but not so deep they crush the board’s face. Once every panel is up, tape and mud the seams the same way a drywall joint would be finished, using the alkali-resistant tape mentioned above and a setting compound rated for wet areas rather than standard joint compound.

Where to Start Tiling Around a Bathtub

Not on the tub itself, and this trips up more first-time installers than anything else on this list. Bathtubs settle and flex slightly, and even a well-installed one is rarely dead level along its full length. Starting the first row of tile directly on the tub lip bakes that unevenness into every row above it, and by the third or fourth course the grout lines are visibly drifting.

Snap a level line partway up the wall instead, using an actual level or a laser rather than the tub as a reference. That line marks where the second row of full tiles starts. Set the field tiles from that line upward, working outward from the centre of the back wall so any cut pieces land evenly at both corners instead of a full tile on one side and a sliver on the other. The bottom row, the one that meets the tub, gets scribed and cut to fit last, once every full tile above it is set and true. It’s slower than working straight up from the tub, but it’s the difference between grout lines that read straight and ones that visibly lean by the far end.

The 3-4-5 Rule for Tiling Square Corners

Bathtub alcoves are almost never perfectly square, and a corner that’s even slightly off will show up as a widening or narrowing grout line running the height of the wall. The 3-4-5 rule checks a corner without needing a framing square. Measure three feet along one wall from the corner and four feet along the other, mark both points, then measure straight between those two marks. Exactly five feet means the corner is a true 90 degrees.

Off by half an inch on that diagonal, and the tile lines will visibly drift by the far wall even though nothing looked wrong when the first tile went in. Worth checking both back corners of the surround before laying a single tile, not just the one that looks the most obviously off.

Cutting Tile Around the Tub Spout, Faucet, and Trim

Every tub surround has at least three fixtures that need a cut or a hole: the spout, the valve trim, and usually a soap dish or shelf recess. A hole saw sized to the fixture’s escutcheon plate handles round cutouts cleanly, and it’s worth dry-fitting the trim piece before committing to a cut, since escutcheons vary more between valve brands than people expect. For anything closer to a wall edge or window trim, a wet saw does the straight run and a tile nipper chews back the corners a piece at a time rather than risking a crack from one aggressive cut.

Back-buttering, spreading a thin layer of thinset directly on the tile itself in addition to the wall, matters more around fixture cutouts than anywhere else on the surround. Those pieces get handled more during fitting, and a dry spot under a cut tile shows up eventually as a hollow sound and a loose corner.

Grouting and Caulking: What Goes Between the Tub and the Tile

Grout at the field of tile, caulk at the tub joint. That single distinction is the second most-skipped step on this whole job, right behind waterproofing. The line where tile meets the top of the tub needs to flex slightly every time the tub fills with water and the weight shifts the structure underneath it, even by a fraction of an inch. Rigid grout in that joint cracks within a season. A paintable or pre-matched silicone caulk in the same colour as the grout handles that same joint without cracking, because it’s designed to move.

Every other seam, tile-to-tile across the field, inside corners, gets grouted normally once the thinset has cured, typically 24 to 48 hours depending on the product and the room’s humidity. Pick the caulk colour to match the grout before starting, not after, since caulk and grout from different manufacturers rarely land on an identical shade even when both are labelled the same name.

Common Mistakes on a Tub Surround

Starting the first row on the tub lip instead of a level line ranks first, and it’s the mistake that’s hardest to see coming since the tub looks flat enough by eye. Skipping the waterproofing membrane or treating it as optional ranks a close second, mostly because the consequences don’t show up until well after the job is done. Grouting the tub-to-tile joint instead of caulking it is third, common enough that plenty of finished surrounds develop a cracked line right at the tub within the first year. Rounding those three out: not accounting for the tub flange with furring strips, which throws the whole wall out of plane before the first tile goes up, and rushing grout in before the thinset has properly set, which leaves grout lines that crumble or discolour early. If anything here doesn’t match what you’re looking at, get in touch and we’ll work through it with you.

Frequently Asked Questions

Where to start tiling around a bath?

Off a level line snapped partway up the wall, not the tub itself. Tubs are rarely perfectly level along their length, and starting the first row on the tub lip carries that unevenness into every row above it.

What is the 3 4 5 rule for tiling?

A geometry check for square corners using basic measurements instead of a framing square. Three feet one way, four feet the other, and a five-foot diagonal between those two marks confirms a true 90-degree corner.

Do you install a bathtub before tiling?

Tub first, every time. It gets set, levelled, and anchored, with the plumbing rough-in positioned correctly, before backer board or tile goes up around it.

What do you put between tub and tile?

Caulk, not grout. The joint where tile meets the top of the tub needs to flex with the tub as it fills and settles, and rigid grout in that spot cracks within a season. Colour-matched silicone caulk handles that movement without failing.

A tub surround is one of those jobs where the parts nobody sees decide whether it holds up for twenty years or starts leaking behind the wall in two. If the furring strips got skipped, the membrane looks thin in spots, or the back corners aren’t reading square on a first check, that’s worth a second opinion before the first tile goes up over a problem that’s still there. A proper bathroom tile assessment from someone who tiles tub surrounds for a living catches what a weekend DIY walkthrough usually misses.

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Jordan Tile & Stone

Tile installation and repair across central Vancouver Island: Campbell River, Courtenay, Comox, Oyster Bay, Nanoose Bay, Parksville, Qualicum Beach and Nanaimo.

Phone: (250) 201-3891
Hours: Monday to Sunday, 7:00 am to 6:00 pm
Address: 4423 Patricia Rd, Oyster Bay, BC V9H 1B8