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Do you need a waterproofing membrane behind shower tiles?

Tiles and grout are not fully waterproof on their own, so walls and floors in a shower area usually need a waterproofing membrane or a waterproof board underneath. Which kind suits depends on the wall, the floor and whether it is a tray shower or a level wet room.

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Why are tiles and grout not enough?

Tiles look waterproof, and glazed tiles do shed water well. The weak points are the joints. Grout is fine but not waterproof, especially cement-based grout, and silicone at the corners and edges ages and can pull away. Over time water finds its way through, and what sits behind the tiles gets wet.

If the wall behind is plain plasterboard or old plaster, it can soften, swell and grow mould long before anything shows on the surface. Tiles start to sound hollow, grout cracks, and the damage spreads into the next room or the ceiling below.

A waterproofing membrane is a layer behind the tiles that stops water reaching the wall or floor, even when grout and silicone are no longer perfect. Our tilers and bathroom fitters pages cover the trades that fit them.

QuoteZila starts in Cheshire, with Crewe, Nantwich and Sandbach first, and anyone in the UK can post a shower job.

What types of membrane are there?

Liquid membranes. A paint-like coating brushed or rolled onto the wall and floor in two or more coats, with reinforcing tape at corners and joints. They suit awkward shapes and small areas.

Sheet membranes. Thin waterproof sheets bonded to the wall with adhesive, with overlapping joins and pre-formed corners. They give an even thickness.

Waterproof backer boards. Foam or cement-based boards that are waterproof themselves. The joints and screw holes are sealed with tape and sealant, and the boards replace plasterboard in the shower area.

Shower kits. Many makers sell kits with a membrane, tape, corner pieces and pipe collars, for one shower enclosure.

Each product has its own instructions for the base it suits, how many coats, overlaps and how long to wait before tiling. A good fitter follows those to the letter.

Where does the membrane go?

In a tray shower, the membrane usually covers the walls inside the enclosure and laps down over the upstand at the edge of the tray, so water running down the wall drops into the tray and not behind it.

In a wet room, where the floor is level and drains to a gully, the whole floor is waterproofed, with the membrane running up the walls around the room. The joint between the floor and the drain needs a proper collar or flange.

Weak spots that need extra care include:

  • internal and external corners
  • where the wall meets the tray or floor
  • pipe and valve openings through the wall
  • the edge of a recess or niche
  • screw holes and board joints

Does a membrane solve condensation?

No. A membrane keeps water from getting behind the tiles. It does nothing about steam in the room. GOV.UK says moisture from everyday activities such as showering builds up in the air if it cannot be removed, and that kitchens and bathrooms need adequate ventilation [S1]. A working extractor fan and a window you can open matter as much as what is behind the tiles.

If you already have mould on a bathroom ceiling or around a window, GOV.UK says simply removing surface mould will not stop it coming back [S1]. Fix the ventilation as well as the shower.

What should you ask before the tiles go on?

Ask your tiler or fitter:

  • Which membrane or board are you using, and is it suitable for showers?
  • Which areas will be waterproofed, and how far beyond the shower?
  • How will corners, pipe openings and the tray or drain joint be sealed?
  • How long does the product need before tiling, and will you wait that long?
  • Can I see the waterproofing before it is covered?

Many membranes and adhesives carry safety labels. HSE explains that hazard pictograms, shown as a diamond with a red border, alert us to a hazardous chemical that might cause harm [S2]. If a product carries one, the fitter should follow its safety advice and keep the room ventilated.

Photos of the waterproofing before tiling are worth keeping. They show what was done if a leak appears later.

Jobs you might post

These are examples, not taken from real job posts.

  • "Old tiled shower with cracked grout and a soft wall behind. Please quote to strip, waterproof and retile the enclosure."
  • "Converting a bath to a walk-in shower with a low tray. Please quote including waterproofing and say which system you use."
  • "Small wet room in the downstairs loo. Please quote to waterproof the floor and walls and fit a drain."

Citizens Advice suggests trying to get written quotes from at least 3 different traders before you decide on one [S3]. Our walk-in shower cost guide and shower tray guide cover the wider job. Our guide to what tanking means explains the term.

QuoteZila is free for customers and local businesses [QZ1]. Your job goes to up to five matched local businesses [QZ2].

Honest status: QuoteZila is new. We're starting in Cheshire, beginning with Crewe, Nantwich and Sandbach, and growing area by area. Anyone in the UK can still post a job or register a business. How fast you get quotes depends on how many local businesses have joined near you. Businesses can register and receive jobs straight away. We don't check insurance, qualifications or registrations, so please check these yourself before you hire.

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Questions about shower waterproofing

Is a waterproofing membrane the same as tanking?

In a bathroom the words are often used for the same thing: a waterproof layer behind tiles. Tanking is also used for waterproofing basements and walls below ground, which is a different job. Our page on what tanking means explains both.

Can I tile straight onto plasterboard in a shower?

Standard plasterboard is a poor base in a shower, because it softens if water gets behind the tiles. Ask your tiler about a waterproof backer board or a membrane over a suitable board, and follow the product maker's instructions.

Do I need to waterproof the whole bathroom?

Not always. The shower area and the floor in a wet room take the most water, and a splash zone around a bath may need protection too. Ask the fitter which areas they plan to waterproof and why.

Does QuoteZila check tilers and bathroom fitters?

No. We don't check insurance, qualifications or registrations, so please check these yourself before you hire. You can report a quote or a business from your job page.

This page is general information, not professional or legal advice. QuoteZila does not check Gas Safe, WaterSafe, NFRC, NICEIC or other registrations against the register on your behalf: look them up yourself.

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Sources

  1. QZ1: QuoteZila product fact. QuoteZila home and FAQ copy.
  2. QZ2: QuoteZila product fact. QuoteZila FAQ How does getting quotes work.
  3. S1: Understanding and addressing the health risks of damp and mould in the home, GOV.UK (DHSC and MHCLG). Accessed 2026-11-02. https://www.gov.uk/government/publications/damp-and-mould-understanding-and-addressing-the-health-risks-for-rented-housing-providers/understanding-and-addressing-the-health-risks-of-damp-and-mould-in-the-home--2
  4. S2: Hazard pictograms (symbols), Health and Safety Executive. Accessed 2026-11-02. https://www.hse.gov.uk/chemical-classification/labelling-packaging/hazard-symbols-hazard-pictograms.htm
  5. S3: Before you get building work done, Citizens Advice. Accessed 2026-11-02. https://www.citizensadvice.org.uk/consumer/getting-home-improvements-done/before-you-get-building-work-done/