How to Install a Shower Cubicle & Correctly Seal It

A shower cubicle is only as watertight as the preparation behind it. Even the best enclosure will leak if the tray isn’t stabilised, the walls aren’t waterproofed, or the silicone is applied incorrectly. Most leaks aren’t caused by the enclosure — they’re caused by poor sealing or movement in the tray.

This guide explains how to correctly install a shower cubicle, how to seal it so it stays watertight, and the theory behind why sealing must be done a certain way.

1. Preparing the Area Before Installation

A watertight cubicle starts long before the enclosure is fitted. Preparation is everything.

Fully Tank the Walls

Best practice: Fully tank all shower walls using a bonded membrane system such as Impey WaterGuard. Tanking should extend beyond the enclosure area, covering corners, joints, and pipe penetrations to create a continuous waterproof envelope.

Stabilise the Shower Tray

A tray that moves even slightly will break the silicone seal. To prevent this:

• Ensure the tray is fully supported with no hollow spots
• Use a mortar bed or solid support system
• Check the tray is perfectly level

Recommended: Senstec slip‑resistant trays — extremely rigid and ideal for long‑term sealing integrity.

Fit a Tray Upstand Seal

Recommended: Install a flexible tray upstand system such as Classi‑Seal (other makes available). This creates a waterproof barrier between the tray and wall, absorbing small movements and preventing leaks where the tray meets the wall.

2. Installing the Shower Cubicle

Once the tray and walls are prepared, the enclosure can be installed. Accuracy is essential.

Fix the Wall Profiles

• Mark and drill fixing holes
• Apply a bead of silicone behind the profile (not inside the channel)
• Secure the profile firmly to the wall

Fit the Glass Panels

• Insert the glass into the profiles
• Ensure the panels are plumb and square
• Tighten fixings gradually to avoid stress on the glass

Install the Door

• Fit hinges or rollers according to the manufacturer’s instructions
• Check smooth operation and alignment
• Adjust seals so they sit flush without gaps

3. Correctly Sealing the Shower Cubicle

Why You Should Only Seal the Outside

Shower enclosures are designed with internal drainage channels built into the frame. These channels collect any water that enters the frame and guide it safely back into the tray.

If you seal the inside:

• You block the drainage channels
• Water becomes trapped inside the frame
• It eventually escapes behind the tray or wall
• This causes hidden leaks, mould, and structural damage

By sealing only the outside of the enclosure, you allow the internal channels to function correctly, ensuring any water that enters the frame drains back into the tray exactly as designed.

Tray Slope & Internal Drainage Theory

Shower trays are manufactured with a built‑in slope that directs water toward the waste. This slope also ensures that any water entering the enclosure frame flows back into the tray rather than pooling or escaping.

When the tray is installed level (as it must be), the internal slope handles the drainage. If the tray is not properly supported or becomes uneven:

• Water can pool at the edges
• Internal drainage channels may not function
• Silicone seals become stressed and fail

Where to Apply Silicone

Silicone should be applied:

• Along the outside bottom edge of the enclosure frame
• Along the vertical outer edges where the frame meets the wall
• Around the tray perimeter (outside only)

Where NOT to Apply Silicone

• Inside the enclosure frame
• Inside the bottom frame edge
• Over drainage channels or weep holes

Applying the Silicone

• Use high‑quality, mould‑resistant silicone
• Cut the nozzle at a 45° angle for a smooth bead
• Apply steady pressure for an even finish
• Tool the silicone gently for a clean seal
• Allow 24 hours curing time before use

4. Final Checks & Testing

Before using the shower, carry out a full inspection:

• Check all seals for gaps or thin spots
• Ensure the enclosure is rigid with no movement
• Run the shower and check for leaks around the tray
• Confirm water drains correctly through internal channels