Professional Waterproofing Guide
How to Waterproof Showers, Wetrooms & Bathrooms (By BAL Adhesives)
Waterproofing (often called tanking) is a crucial part of any tiling installation in wet areas. Although tiles themselves are waterproof, tile adhesives and grout are not — meaning water can travel through joints and into the background or substrate if the area isn’t properly protected.
Over time, continued exposure to moisture can lead to black mould, damage to backgrounds, and in worst cases, full tile installation failure. This is why tanking is now commonly recommended across domestic and commercial wet areas.
Best-practice note
British Standards BS 5385-1:2018 recommends that in wet areas (e.g. showers, wet rooms and steam rooms), substrates should be protected with a suitable proprietary tanking membrane system.
One approved solution is BAL Waterproof 1C — a one-coat, ready-mixed waterproofing membrane designed for internal showers, bathrooms and wetrooms. Below is a clear, step-by-step approach to applying it correctly.
What You’ll Need Before You Start
Preparation is everything in wet areas. Before applying any waterproofing membrane, ensure your surface is suitable, stable and ready for tiling.
Key products
- BAL Waterproof 1C (ready-mixed tanking membrane)
- BAL Primer 1C (only required on some substrates)
- Self-adhesive Scrim Tape (corners, junctions, penetrations)
Tools
- Roller (ideal for even coverage)
- Brush (details + joints/cracks)
- 4mm notched trowel (optional method)
- Clean cloths + vacuum/brush for dust removal
Important reminder
Waterproofing is only as reliable as the background beneath it. Always ensure substrates are clean, dry, sound and stable before tanking — and follow manufacturer guidance for drying times between steps.
Substrates: When Priming Is (and Isn’t) Needed
One of the benefits of BAL Waterproof 1C is that on many substrates, it can be applied without priming. However, certain surfaces still require a primer coat first to ensure the waterproofing membrane bonds correctly.
No priming required on most substrates
BAL Waterproof 1C can be applied directly (no primer) onto:
- Plasterboard
- Cement:sand render
- Screeds and concrete
- Plywood overlays
- BAL Board (smooth side)
- BAL Rapid-Mat uncoupling mat system
Prime first on these surfaces
If waterproofing onto plaster, cement boards, or BAL Board on the tiling side, prime all surfaces with:
1 coat of neat BAL Primer 1C applied with a roller or sponge, then allow to dry for 15–30 minutes.
How To Apply BAL Waterproof 1C (8 Easy Steps)
Follow this step-by-step approach to waterproof showers, wetrooms and bathrooms for long-lasting protection. The goal is a continuous, well-detailed membrane across all wet areas — especially corners, junctions and penetrations.
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1) Check the area and prepare the surface
Ensure backgrounds are clean, dry, sound and free from dust. Remove loose materials and ensure boards/joints are secure.
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2) Prime if required
Only prime when waterproofing onto plaster, cement boards or BAL Board (tiling side). Apply 1 coat of neat BAL Primer 1C and allow to dry for 15–30 minutes.
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3) Apply self-adhesive Scrim Tape to critical points
Use Scrim Tape to reinforce and waterproof high-risk junctions before coating the full area.
- Internal and external wall corners
- Wall junctions with base/upstands/columns
- Pipe penetrations, outlets, drainage channels
- Junctions of different base/background materials
- Cracks and board joints over 3mm wide
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4) Brush over the tape with BAL Waterproof 1C
Apply the membrane over Scrim Tape areas to fully embed and seal them. BAL Waterproof 1C is ready-mixed straight out of the bucket — no mixing required.
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5) Apply BAL Waterproof 1C over the whole area
Using a suitable roller, 4mm notched trowel or brush, apply the membrane across walls and floors. For cracks and board joints around 2–3mm, brush coating into joints to ensure they are fully filled.
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6) Achieve the correct thickness on walls
When applying to walls, ensure a minimum membrane thickness of 0.8mm.
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7) Achieve the correct thickness on floors
When applying to floors, ensure a minimum thickness of 1.6mm. This can often be achieved with a roller, but two coats may be required. For best practice, two coats on floors are commonly recommended to help reach the required build.
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8) Allow to dry before tiling
Once applied, allow the membrane to dry for a minimum of 2 hours before tiling with a suitable BAL tile adhesive.
After Waterproofing: Tiling & Grouting Tips
After tanking, choose a tile adhesive and grout that match your substrate and environment. Wet areas often benefit from flexible systems that handle movement, temperature changes and frequent exposure to water.
Adhesive selection
Consider flexible or rapid-setting options depending on the project requirements and turnaround time. Always follow product guidance for coverage and open time.
Grout selection
In showers and wet rooms, choose a grout suitable for wet environments and regular cleaning. For hygiene-critical zones, epoxy grout may be appropriate.
Pro tip
Don’t skip reinforcement at corners, transitions and penetrations. Most wet-area failures start at junctions — scrim tape + correct membrane build is what protects the installation long-term.
Waterproof With Confidence
Use the right BAL waterproofing system to protect your shower, wetroom or bathroom before tiling — and reduce the risk of mould, background damage and costly repairs.
Frequently Asked Questions
Common questions about waterproofing (tanking) showers, wetrooms and bathrooms.
Do I really need to waterproof behind tiles in a shower?
Yes. Tiles are waterproof, but grout and adhesive are not fully waterproof barriers. Without tanking, moisture can travel through joints and potentially damage backgrounds over time.
Which areas should be reinforced with scrim tape?
Use scrim tape at internal/external corners, wall-floor junctions, pipe penetrations, drainage outlets/channels, transitions between different substrates, and cracks or board joints over 3mm.
How long should BAL Waterproof 1C dry before tiling?
Allow the membrane to dry for a minimum of 2 hours before tiling with a suitable BAL tile adhesive. Always follow the product instructions and account for site conditions such as temperature and ventilation.
What membrane thickness is required on walls vs floors?
For walls, apply a minimum thickness of 0.8mm. For floors, apply a minimum of 1.6mm — two coats are often recommended on floors to help achieve the required build.
Can I apply BAL Waterproof 1C straight onto plasterboard?
BAL Waterproof 1C can be applied without priming onto plasterboard on most internal projects. However, always confirm suitability for your exact background and follow the manufacturer’s guidance for your installation.
