How to Waterproof a Shower Before Tiling: A Step-by-Step Tanking Guide

To waterproof a shower before tiling, you prime the walls and floor, tape every corner, joint and pipe, then brush on two coats of liquid tanking membrane and let it cure before any adhesive goes on. That continuous layer, called tanking, is what keeps water out of the walls. The grout and tiles don't.

Grout and tiles take the daily soaking, but they aren't the waterproof layer. Tanking sits behind them as one sealed membrane that stops water reaching the board, the plaster and the timber. Get that layer right and the tiles on top are mostly about looks. Get it wrong and even a top-quality porcelain won't stop a stained ceiling downstairs.

This guide covers what tanking is, where it goes, the order to do things in, how much to buy, and what to check if a shower is already leaking.

In almost every shower build or refit, yes. Tanking is the safest way to create a waterproof barrier behind the tiles, and it costs far less than ripping out a failed shower.

Tiles resist water, but a tiled wall is full of joints. Grout is porous, and tile adhesive isn't a waterproofer. With daily use, water gets through the grout lines into whatever sits behind. Untreated plasterboard or a timber floor soaks up that moisture, swells, softens and eventually fails, and you often don't see it until the damage has spread.

Tanking means applying a waterproof membrane system to the surfaces behind the tiles. That's usually a primer, a liquid membrane (the coating) and a waterproof jointing tape for the vulnerable junctions. Some systems use sheet membranes instead. Either way, the goal is one unbroken, sealed layer.

That's different from a board or finish being "water-resistant". Water-resistant means it copes with splashes for a while. Waterproof means water can't pass through. A shower needs waterproof.

Usually not onto plain plasterboard. Standard plasterboard is paper-faced gypsum, and it breaks down quickly when it stays damp. Moisture-resistant (green) plasterboard is only resistant, not waterproof.

If plasterboard is already on your walls, you have two options:

1. Take it out, replace it with a tile backer board made for wet areas, then tank over it.
2. Keep it and apply a tanking system that is approved for use over plasterboard, following that manufacturer's priming instructions exactly.

Check each system's data sheet for the surfaces it's approved for. A sealed, continuous tanking layer matters more than which tile you pick. A budget ceramic over a well-detailed membrane will outlast a premium tile on a half-sealed wall.

Focus on the wet zone: the shower walls, the shower floor or tray area, and the junctions where they meet. Walls away from direct spray, like the wall behind your basin, don't normally need the same treatment.

Where the membrane should go:

1. Shower walls, from the floor up to at least the height your system recommends. Many people tank to full tiling height, which is the simplest rule to follow.
2. The shower floor in a wet room, plus an upstand where the floor meets the wall.
3. Around tray edges, niches, benches and shower screen fixing points.
4. A little beyond the enclosure where water splashes, or across the whole floor if you're building a full wet room. Our guide to wet room design ideas covers the layout side.

Water tests every joint, corner and pipe over time, so the closer you are to the shower head, the less room there is for shortcuts.

Yes, if you want the shower to stay watertight for years rather than months. The membrane sits between the substrate (the board or screed) and the tile adhesive.

In practice, a "membrane under shower tiles" means three things working together: primer to prepare the surface, liquid or sheet membrane to form the barrier, and sealing tape at every corner and joint. A membrane with no tape at the corners has weak spots built in.

Cement board is water-resistant, which makes it a far better base than plasterboard. It won't rot or crumble when it gets wet. It isn't a waterproofing system on its own, though, so you still need to tank it.

Water doesn't only damage the board. It passes through board joints, around screw heads and past pipe holes into whatever's behind, and the board itself can absorb moisture and carry it to the framing. Some boards come with a factory coating or their own joint-sealing system, so read the board manufacturer's instructions. If they say the joints need a membrane, follow that.

Shower wall surfaces at a glance

Kits differ in the details, so read the instructions in your tub first. The order of work is much the same across most systems.

1. Prepare the substrate

The surface needs to be sound, clean, dry and flat. Fix boards firmly with the screws and washers the board manufacturer specifies, at the spacing they recommend. If you're building a wet room floor, form the falls to the drain now, because the membrane won't fix standing water later. Vacuum off dust, fill any gaps or damaged areas, and remove anything loose.

2. Prime

Most kits include a primer. It helps the membrane bond and controls how much moisture the surface absorbs. Apply it with a brush or roller and let it dry for the time on the tub. Skipping primer is one of the quickest ways to a coating that peels.

3. Tape first

Before the full coat goes on, bed waterproof jointing tape into a wet layer of membrane at every high-risk spot:

1. Internal and external corners
2. Wall-to-floor junctions
3. Board joints
4. Around the drain or waste outlet
5. Around pipes

Press the tape flat with no creases or air bubbles, and overlap the ends rather than butting them. Self-adhesive tape, such as AquaTank Self-Adhesive Tape (5m and 10m rolls), makes this stage quicker for first-timers. Pre-formed pieces like the Arc Internal Corner and Arc External Corner save you folding tape into corners.

4. Apply the membrane

Brush or roll on the first coat, keeping it continuous over the taped areas and the whole surface. Once it's dry to the touch, apply the second coat, ideally at right angles to the first so any thin patches get covered. Most manufacturers specify the number of coats and the thickness, so follow that rather than judging by eye.

If you can see the board through the coating, it's too thin.

5. Detail the shower tray, pipes and drain

Now go back to the awkward spots. Seal around pipes with the collars supplied or recommended with your system, and fit the correct drain detail for a wet room floor, with the membrane lapping onto the drain flange as the manufacturer says.

If you're fitting a shower tray, seal the joint between the tray and the wall before you tank. Stick a shower tray sealing tape along the tray upstand and up onto the wall, then lap the tanking membrane over the wall side of the tape. This is the joint that moves most when someone stands in the tray, and it's the most common place for a shower to leak.

6. Let it cure, then tile

Don't rush this. Drying times vary between systems and with room temperature, so use the time printed on your Botament, AquaTank, Bostik or Evo-Stik tub, not a general rule. Cold, damp rooms slow everything down, so keep the bathroom warm and ventilated.

Once it's cured, tile with a flexible, wet-area adhesive and grout with a wet-area grout. Check that your adhesive is compatible with the membrane. It's on the data sheet. If you need to drill through the finished tiles for a screen or rail, our guide on how to drill through tiles explains how to do it without cracking them.

If you're building a wet room floor, many installers run a flood test before tiling. It's worth doing when the floor sits above a living space.

Pro tip: Before you tile, take photos of every taped corner, pipe collar and the tray joint. If a leak ever appears, you'll know exactly what's behind each tile without guessing.

Get everything together before you start. Stopping halfway for a missing roll of tape is how corners get skipped.

Tanking materials

1. Primer suited to your substrate
2. Liquid waterproof membrane (or sheet membrane)
3. Waterproof jointing tape, enough for every corner, junction and board joint

Detailing parts

1. Pre-formed internal and external corners, if your system uses them
2. Pipe collars for taps, shower valves and pipework
3. Shower tray sealing tape, if you're fitting a tray
4. A compatible drain or waste seal for a wet room floor

Substrate items

1. Tile backer board or another wet-area board
2. The board manufacturer's screws and washers
3. Board joint treatment, where the manufacturer requires it
4. Floor leveller or screed, if you're forming falls

Tiling materials

1. Flexible, wet-area tile adhesive
2. Wet-area grout
3. Bathroom silicone for movement joints and the tray or bath junction

Tools

1. Paintbrush and short-pile roller
2. Notched trowel
3. Mixing paddle and bucket
4. Scissors, tape measure and pencil
5. Protective gloves

There's no single winner, because the right kit depends on your shower. Compare these four things:

1. Whether the parts work together. Primer, membrane and tape should be designed as one system, and ideally your adhesive too.
2. Coverage. Check the m² on the tub, and whether it's for one coat or the full system.
3. Drying time. This matters if your tiler is booked for a set day.
4. Tape. Check whether jointing tape is included and whether there's enough for your corners and floor perimeter.

Our tanking kits and tape range includes complete kits from Botament, AquaTank, Bostik, Evo-Stik and Arc:

1. Botament Tanking Kit With Self-Adhesive Tape: a complete kit with tape that sticks straight on, for showers, wet rooms and around baths.
2. AquaTank Kit: membrane and tape in one box. AquaTank Neo-Flex Membrane is also sold on its own in 5kg and 10kg tubs if you need extra coverage.
3. Bostik Flexible Tanking System Kit (8kg) and Evo-Stik Technik Flexible Tanking System (7kg and 9kg kits): flexible systems suited to larger showers and wet rooms.
4. Arc Premium Tanking Kit: a complete kit, with matching Arc internal and external corners sold separately.

If you already have a kit and just need extra tape for a long wall-to-floor run, AquaTank Self-Adhesive Tape comes in 5m and 10m rolls.

Most kits in the range are listed with delivery in 1-2 days and are available to collect, so you can have everything before your tiler arrives. Check the product page for current stock. If you're unsure about quantities or which parts go together, our showroom staff can help.

Measure each surface you'll tank, work out its area, add them together, then add an allowance. It's the same method as working out how much tile you need.

1. Measure the width and height of each wall you'll tank, in metres, and multiply to get m².
2. If you're building a tiled wet room floor, measure the floor (width x depth) too. If you're fitting a shower tray, leave the floor out, because the tray itself doesn't get tanked.
3. Add all the areas together.
4. Add roughly 10% for overlaps, corners and upstands.
5. Check whether the kit's stated coverage is for both coats.

Worked example: a 900mm x 900mm alcove shower, tanked to 2.1m high.

1. Back wall: 0.9 x 2.1 = 1.89m²
2. Two side walls: 2 x 1.89 = 3.78m²
3. With a shower tray: walls only = 5.67m², plus 10% = about 6.2m²
4. As a tiled wet room floor: add the floor (0.9 x 0.9 = 0.81m²) = 6.48m², plus 10% = about 7.1m²

The Arc Premium Tanking Kit, for example, is listed as covering 5m², so one kit isn't enough for either version of this shower. You'd need a second kit, or extra membrane such as an AquaTank Neo-Flex Membrane tub, plus spare tape. If your shower is smaller, or you're only tanking part of the wall height, 5m² might be plenty.

Round up rather than buying to the centimetre. A half-used tub of membrane costs less than running out with one coat to go.

Sometimes, but it's rarely the best choice. Most systems need a prepared surface, and old tiles cause problems:

1. If the tiles are loose or the bond is weak, the new layer is only as stable as what's under it.
2. Grout lines leave ridges and gaps that the membrane has to bridge.
3. Soap residue, limescale and old sealant stop primer bonding.
4. Movement in the old tiling will crack the membrane above.

Inspect first. Tap every tile and listen for a hollow sound, and try to lift any loose ones. Clean thoroughly, then check the tanking manufacturer's instructions. If they don't explicitly allow tanking over tiles, strip the old tiles and adhesive back to a sound base. Stripping out is messy, but it's less work than doing the whole shower twice.

Often it isn't the grout. It's the layer behind it. These are the most common causes:

1. Gaps in the waterproofing at corners, board joints or pipes. Missing tape, poorly bedded tape or gaps around pipes are the usual causes. The fix is to strip the tiles in that area and redo the tape and membrane.
2. Membrane applied too thin, unevenly, or without primer. Thin patches let water through, and a coating that never bonded can lift. The affected tiles need to come off so the area can be recoated.
3. Tiles laid before the membrane had cured. Trapped moisture weakens the coating and spoils the bond. Always wait the full drying time on the tub.
4. Adhesive or grout not suitable for a wet area, or not compatible with the membrane. Check both data sheets.
5. No flexible sealant at movement joints. Where the tray meets the wall, in internal corners and around the screen, rigid grout cracks and water gets in. Use bathroom silicone in these joints.

Find the source before you repair anything. Check the obvious spots first: corners, the tray edge, the shower valve and the waste. If you can't find it, a moisture meter or a plumber's visit is worth the cost before you start removing tiles.

Measure your shower, add 10%, and choose a kit with enough coverage plus spare tape. Browse our tanking kits and tape, shower sealing tape and bathroom silicone online, or call into one of our showrooms in Ballymount, Coolock, Deansgrange or Ashbourne, open seven days a week. Find your nearest showroom.

We offer extremely competitive pricing on our entire range of tiles, paving, wall panelling and likewise. We stock a huge range of wall and floor tiles, and our prices are competitive for retail and trade. Our stock is widely available in our tile stores in Ireland, which are open 7 days a week.

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