Shower Grout Repair or a New Bathroom? How to Tell

Cracked grout is often the first thing an Auckland homeowner notices in a shower, and not always the thing that's wrong. A hairline split in a corner. Black lines in the floor joints. A patch that stays grey however hard you scrub.

Sometimes that really is a grout problem, and a regrout sorts it for a fraction of the cost of a renovation. Sometimes the grout is just the part you can see.

Shower grout repair fixes grout. It doesn't fix waterproofing, framing or plumbing, and those are the three things behind the tiles that decide whether a regrout will last. Below: how to read the symptoms, when a regrout is the right call, when it only buys time, and what we find when we open up a shower that's been patched before.

If you're weighing up the grout itself, our team has written a detailed comparison of epoxy grout and cement grout for NZ bathrooms, covering cost, where each one belongs and the products available here. This article starts one step earlier: working out whether the grout is the problem at all.

What grout does in a shower, and what it doesn't

Grout fills the joints between tiles. It stops dirt and water sitting in the gaps, locks the tile edges and gives the wall a finished surface. What it doesn't do is keep water out of the wall.

Tiles and grout aren't waterproof on their own. In a properly built shower, the waterproofing is a membrane applied to the floor, the walls to the required height and every junction where they meet, before any tile goes on. In New Zealand that work sits under Building Code clause E3 Internal Moisture. Household wet areas are usually built to its Acceptable Solution, E3/AS1, with the membrane meeting AS/NZS 4858, the standard for wet-area waterproofing membranes. The floor is laid to a fall so water runs to the waste instead of pooling.

So a shower has two layers doing two different jobs. The tile and grout are the wearing surface. The membrane is the waterproofing. A cement grout joint can crack, stain and grow mould for years without any water reaching the framing, as long as the membrane underneath is intact. And a shower with perfect-looking grout can still be leaking, if the membrane failed or was never there.

So the useful question is what the grout is telling you about the layer underneath.

Reading the symptoms: grout problem or something deeper?

Take a torch and a screwdriver into the bathroom and check these in order. No single one is a diagnosis. Together they show which way the job is heading.

Grey, stained or mouldy grout in the middle of the wall

This is almost always a grout and ventilation problem, not a leak. Cement grout is porous. It absorbs soap, body oils and moisture, and in a bathroom without a fan ducted to the outside, mould grows in it. Discoloured grout on an otherwise solid wall is the classic case where a regrout, plus a better extractor fan, genuinely fixes it.

Cracks at the internal corners and where the wall meets the floor

These are movement joints. Two surfaces meeting at an angle move against each other as the house moves, and grout of any kind cracks there eventually. Those junctions should be filled with a flexible sanitary silicone, not grout. A cracked corner on its own usually means the wrong material was used, and the fix is to rake it out and silicone it properly. If the crack is wide, the tiles either side sound hollow, or the silicone keeps failing within months, something is moving more than it should.

Loose, drummy or cracked tiles

Tap the tiles with the handle of a screwdriver. A solid tile gives a sharp click, while a hollow, drummy sound means it has lost its bond with the wall or floor. A regrout won't hold on a tile that's moving, because the new grout is being asked to do the adhesive's job. One or two loose tiles can sometimes be lifted and re-fixed. A whole area of drummy tiles, especially on the shower floor, usually points to water getting behind them.

Staining, swelling or soft spots outside the shower

This is the one to take seriously. Check the skirting outside the shower, the bottom of the vanity, the floor covering in the next room and the ceiling below if the bathroom is upstairs. Swollen timber, lifting vinyl, a musty smell that never clears or a floor that flexes near the shower all suggest water is travelling somewhere it shouldn't. At that point the grout is a symptom, and regrouting only covers up the evidence.

Is it the shower or the plumbing?

Not every wet wall is a waterproofing failure. A leaking mixer or a pipe behind the wall can do the same damage. There's a simple way to separate them. Superior Property Services' guide to water leak detection in Auckland walks through the meter test Watercare recommends: turn everything off, read the meter, use no water for at least four hours, then read it again. If the meter has moved, pressurised water is escaping somewhere on your side of it.

Know its limit, though. The meter test only catches leaks in pipes under pressure. Water getting through grout and past a failed membrane has already come out of the shower head, so it never registers. A clean result rules out the supply pipes, and says nothing about the shower itself.

When shower grout repair is the right call

A regrout is a proper repair when all of these are true:

• The tiles are sound. No drummy areas, no cracked tiles, nothing lifting.
• There's no damage outside the shower. Skirting, vanity, flooring and the ceiling below are all dry and solid.
• The problem is the grout's look or surface: discolouration, mould, erosion or small cracks in the middle of the wall.
• You're happy with the layout and the tiles for the next several years.

Done properly, a regrout means raking the old grout out to a proper depth, not skimming new grout over the top. Our guidance is at least half the tile depth. A thin skim over old grout is the most common shortcut in shower repairs, and it rarely lasts because the new layer is too thin to bond or to survive a scrub. The corners and the wall-to-floor junction should be resealed with silicone at the same time.

A job this size doesn't need a renovation company. Our sister company Superior Property Services handles minor bathroom alterations such as resealing a leaking shower with a fixed quote before any work starts.

We would much rather tell someone their shower only needs a regrout than sell them a bathroom they don't need. The showers that worry us are the ones that have already been regrouted twice. If the grout keeps failing in the same place, the problem isn't the grout.

When regrouting only buys time

A pattern the Superior Renovations bathroom team sees often in older Auckland houses is a shower that's been regrouted, resealed and regrouted again, each time looking fine for a year or two. Repeated grout failure in the same spot is one of the clearest signs that water is getting past the surface.

Regrouting is unlikely to be the lasting fix when:

• Tiles on the shower floor are drummy or have cracked.
• There's staining, swelling or rot outside the shower, or on the ceiling below.
• The shower was built before modern membranes were routine and you have no record of what's behind the tiles.
• The same joints have cracked again within a year or two of the last repair.
• The silicone at the base keeps coming away, which can mean the floor is flexing.

Housing stock matters here. A 1970s brick-and-tile in Pakuranga, a 1960s weatherboard family home in Massey or a villa in Mt Eden that had its bathroom done decades ago can each have a shower built with very little between the tiles and the framing. When older bathrooms are stripped, the common finds are deteriorated or absent waterproofing, framing rotted by years of water getting in, and previous renovations done cheaply. None of that is visible from the shower tray.

Built before 2000? Don't start chipping tiles yourself. Some older linings, floor coverings and adhesives contain asbestos, and they need testing before anyone breaks into them.

A leak that became a two-bathroom renovation in Massey

Chris and Hang's Massey home had two tired bathrooms. The main one was small, dated and badly laid out, and a bulky acrylic shower made it feel smaller still. Then it started leaking. Rather than fix the leak and live with the rest, they redid both bathrooms, one after the other.

Instead of just repairing the leak we thought we might as well do the whole thing.
— Chris, Massey homeowner

Our lead designer Dorothy Li reworked the main bathroom's layout and we built a custom tiled shower with clear, custom glass in place of the old enclosure. The part you can't see is what made it last: the wet area was sealed with a membrane before any tile went on, the floor was laid to fall to the waste, and every junction was detailed. You can read the full Massey two-bathroom renovation case study on our website. The photo below shows the finished main bathroom.