Bathroom Plastering: Which Plaster to Use in Wet Areas

Bathrooms present unique challenges for plastering. The combination of steam, splashing water, and constant humidity means traditional plastering materials simply won’t hold up. I’ve seen countless bathroom renovations where homeowners or inexperienced tradesmen used standard plasterboard and multi-finish, only to find it bubbling, sagging, and growing mould within six months.

This guide covers exactly which materials work in wet areas, where to use them, and how to ensure your bathroom plastering job lasts decades rather than months.

Understanding Moisture Levels in Different Bathroom Zones

Not all bathroom surfaces face the same moisture exposure. The IET Wiring Regulations divide bathrooms into zones based on water risk, and the same thinking applies to plastering materials.

The key principle: The closer to direct water contact, the more robust your moisture protection needs to be. Standard building materials are only suitable in areas with ambient humidity and proper ventilation.

Why Standard Gypsum Plaster Fails in Bathrooms

Regular plasterboard (pink/ivory board) and multi-finish plaster are made from gypsum, which is hygroscopic — it absorbs moisture from the air. In bathrooms, this creates multiple problems:

• Surface degradation: Gypsum softens when wet, causing the plaster to lose adhesion and bubble away from the substrate
• Structural sagging: Water-saturated plasterboard becomes heavy and loses rigidity, leading to visible sagging between joists or studs
• Mould growth: The paper facing on standard plasterboard provides perfect food for black mould once damp
• Rapid deterioration: Even indirect splash zones will show damage within 6-12 months

I’ve stripped out bathrooms where standard board was used behind tiles. The plasterboard was literally falling apart behind the tiles, held together only by the tile adhesive. This is a ticking time bomb — eventually the tiles lose support and the whole lot comes down.

Best Moisture-Resistant Plasterboards for Bathrooms

Moisture-resistant plasterboard forms the foundation of proper bathroom plastering. These boards have water-repellent additives in the gypsum core and treated paper facings.

British Gypsum Moisture Resistant Board

British Gypsum’s moisture-resistant range (recognisable by the green paper facing) is the industry standard. The boards contain silicone additives that repel water while maintaining the workability of standard plasterboard.

Specifications:

• Available in 12.5mm thickness (standard) and 15mm (higher impact resistance)
• Water absorption under 5% compared to 25%+ for standard board
• Cost: £8-12 per sheet (2400mm x 1200mm) from Travis Perkins or Jewson
• Suitable for Zones 2 and outside zones

Knauf Aquapanel

For Zone 1 areas, Knauf Aquapanel offers cement-based boards that are completely waterproof. These have a cement core with fibreglass mesh reinforcement rather than gypsum.

• Completely unaffected by water immersion
• Significantly heavier than plasterboard (challenging for overhead installation)
• Cost: £25-35 per sheet
• Can be tiled directly without additional tanking in most applications

Cement-Based Renders and Plasters for Wet Areas

For areas requiring direct water resistance, cement-based materials outperform gypsum products every time. These create a waterproof, durable surface ideal for tiling.

Sand and Cement Render

The traditional approach uses a 4:1 sand to cement mix (sometimes 5:1 for undercoats). This creates a completely waterproof base layer.

Application details:

• Mix ratio: 4 parts sharp sand to 1 part Portland cement
• Apply in two coats: 10-12mm scratch coat, 8-10mm finishing coat
• Total drying time: 2-3 weeks minimum before tiling (1 week per 5mm thickness)
• Cost: approximately £3-5 per square metre in materials

The main disadvantage is drying time. You cannot rush cement render — tiling too early traps moisture and causes adhesion failure. For our detailed guide on achieving perfect finishes, see our article on how to skim coat a wall.

Limelite Tough Coat

Modern cement-based plasters like Limelite Tough Coat offer faster drying times while maintaining water resistance. This product bridges the gap between traditional render and gypsum plaster.

• Single-coat application possible up to 25mm thickness
• Can be tiled after just 7 days (versus 14-21 for sand/cement)
• Smooth finish suitable for direct painting in non-wet zones
• Cost: £8-10 per 25kg bag (covers approximately 2.5m² at 10mm thickness)

I use Tough Coat extensively for bathroom renovations. It’s particularly useful on brick or blockwork where you need both levelling and water resistance in one application.

Weber Rend-Aid and Similar Products

Polymer-modified cement renders like Weber Rend-Aid add flexibility and improved adhesion to traditional sand/cement mixes:

• Reduces cracking from substrate movement
• Improves adhesion to difficult substrates (painted surfaces, concrete blocks)
• Slightly faster drying than pure sand/cement
• Mix at 1-2 litres per 25kg cement bag

Specialist Bathroom Plastering Systems

Tile Backer Boards

In Zone 0 and Zone 1 areas (shower cubicles, above baths), tile backer boards provide the most reliable waterproofing. These cement-fibre composite boards are designed specifically for wet area tiling.

Popular options include:

• Marmox boards: Lightweight insulated backer boards (£30-45 per 1200x600mm sheet)
• Wedi boards: Premium extruded polystyrene core with cement facing (£40-60 per sheet)
• Hardie Backer: Budget-friendly cement-fibre boards (£15-25 per sheet)

These boards install directly onto timber studs or masonry using appropriate fixings. The joints require taping with waterproof tape and tanking compound. Once installed and taped, you have a completely waterproof substrate ready for tiling.

Tanking Systems

Even with moisture-resistant boards, tanking membranes provide an extra insurance policy against water penetration. Products like BAL WP1 or Mapei Mapelastic create a flexible waterproof membrane.

Application process:

• Apply to moisture-resistant board or cement render
• Two coats required (apply second coat perpendicular to first)
• Pay special attention to corners, pipe penetrations, and joints
• Use reinforcing tape at all joints and corners
• Allow 24-48 hours drying between coats
• Cost: £25-40 per 5kg tub (covers approximately 5-7m² with two coats)

Plastering Over Existing Tiles in Bathrooms

Many bathroom renovations involve plastering over existing tiles. While possible, this requires careful consideration and proper preparation.

When you can plaster over tiles:

• Tiles are firmly adhered with no loose or hollow-sounding areas
• Surface has been thoroughly cleaned and degreased
• You’re willing to accept the reduced room size from additional thickness
• Tiles are ceramic or porcelain (not natural stone which may crack under plaster weight)

Recommended approach:

• Clean tiles thoroughly with sugar soap or degreaser
• Apply a bonding agent like SBR (Styrene Butadiene Rubber) diluted 1:1 with water
• While tacky, apply a cement-based render as the base coat
• Build up in layers of max 10mm per coat
• Finish with your choice of skim or leave textured for tiling

Honestly, I usually recommend removing tiles rather than plastering over them. It’s more work initially but gives you a better starting point and doesn’t reduce room dimensions. For more information on dealing with problematic surfaces, check our guide on common plastering problems and fixes.

Ventilation: The Often-Overlooked Critical Factor

Even the best moisture-resistant materials will struggle without adequate ventilation. Building Regulations Approved Document F sets minimum ventilation requirements for bathrooms.

Minimum requirements:

• Natural ventilation: Openable window with minimum 1/20th of floor area opening
• Mechanical ventilation: Extract fan minimum 15 litres/second (intermittent) or 8 litres/second (continuous)
• Fan should run for at least 15 minutes after bathroom use (overrun timer)
• Ducting must be smooth, insulated, and terminate externally (not into loft space)

I’ve remediated countless mouldy bathrooms where the materials were correct but ventilation was inadequate. A £40 bathroom extractor fan with humidistat control will save you thousands in future replastering costs.

Step-by-Step: Plastering a Shower Area

Here’s how I approach a typical shower enclosure installation — this represents best practice for Zone 1 areas in 2026.

Materials required:

• Tile backer boards (Marmox or Wedi)
• Stainless steel screws and washers
• Waterproof sealing tape
• Tanking compound (BAL WP1 or equivalent)
• Tile adhesive (flexible, cement-based)
• Grout (epoxy for wet areas)

Process:

1. Frame preparation: Ensure timber studs are straight, plumb, and spaced max 400mm centres. Treat timber with wood preserver.
2. Board installation: Fix backer boards with stainless screws at 200mm centres, keeping screws minimum 15mm from edges. Use washers to prevent screw heads pulling through.
3. Joint treatment: Apply waterproof tape over all joints, bedding in tanking compound. Pay special attention to corners — use pre-formed corner tape where available.
4. First tanking coat: Apply tanking compound in vertical strokes across entire surface including taped joints. Extend 150mm beyond wet area boundaries.
5. Second tanking coat: After 24 hours, apply second coat in horizontal strokes. This cross-coating ensures complete coverage.
6. Tiling: After 48 hours, fix tiles using flexible cement-based adhesive. Use 3mm spacers for grout lines in shower areas.
7. Grouting: Use epoxy grout in shower areas — it’s waterproof and resistant to mould. Standard cement grout will eventually discolour and fail.

Total time for this process: 5-7 days including drying times. Attempting to rush any stage risks long-term failure.

Cost Breakdown: Bathroom Plastering Materials (2026 Prices)

Understanding material costs helps with budgeting. These are typical trade prices from Screwfix, Wickes, and Travis Perkins as of 2026.

Labour costs vary by region but expect £150-250 per day for a qualified plasterer in Kent and the Southeast. A typical bathroom (walls only, no ceiling) takes 2-3 days for preparation, boarding, and rendering/tanking. For comprehensive pricing information, see our complete plastering costs guide.

Common Mistakes to Avoid

After 15+ years plastering bathrooms, I’ve seen these errors repeatedly. Learn from others’ mistakes:

1. Using standard plasterboard “because it’s getting tiled anyway”
The tiles aren’t waterproof — water migrates through grout lines. The substrate must be moisture-resistant regardless of finish.

2. Insufficient drying time before tiling
Cement-based materials release moisture as they cure. Tiling too soon traps this moisture, preventing proper curing and causing adhesion problems.

3. Inadequate joint treatment
Joints between boards are the weakest point. Every single joint must be properly taped and waterproofed — no exceptions.

4. Forgetting thermal movement
Bathrooms experience temperature swings from hot showers. Leave 3-5mm expansion gaps at perimeters and use flexible sealant, not grout, at changes in plane (wall to floor, wall to bath).

5. Poor substrate preparation
Painting directly onto cement render without primer causes paint adhesion failure. Use a suitable primer (acrylic or alkali-resistant) after render has fully cured.

6. Neglecting behind-the-scenes areas
The wall cavity behind backer boards should be ventilated to prevent condensation buildup. Don’t seal cavities completely — leave small ventilation gaps at top and bottom.

Alternatives to Traditional Plastering in Bathrooms

Sometimes plastering isn’t the most practical solution. Consider these alternatives depending on your requirements:

PVC Wall Panels

Completely waterproof plastic panels that click together over battens. Popular in budget renovations and rental properties.

• Advantages: 100% waterproof, very fast installation, easy to clean
• Disadvantages: Looks cheap, can appear dated, limited colour choices
• Cost: £15-30 per m² including battens and trims

Acrylic/ABS Shower Panels

Large-format panels (typically 2400mm high) that eliminate grout lines almost entirely.

• Advantages: Very fast installation, minimal maintenance, modern appearance
• Disadvantages: Limited design options, visible joints, can crack if impacted
• Cost: £120-300 per panel set (typically 2-3 panels needed)

Waterproof Plasterboard with Direct Decoration

For areas outside Zone 1, moisture-resistant plasterboard can be painted directly without tiling.

• Use moisture-resistant board throughout
• Apply bathroom-specific primer (containing anti-mould agents)
• Use bathroom paint with mould inhibitors
• Ensure excellent ventilation
• Expect to repaint every 3-5 years vs. 7-10 years in dry rooms

For design inspiration and current trends in bathroom finishes, explore our complete bathroom renovation guide.

Frequently Asked Questions

Can I use normal plasterboard in a bathroom if it’s not near the shower?

Technically yes, but it’s poor practice. Even areas away from direct water contact experience elevated humidity levels from steam. Moisture-resistant plasterboard costs only £2-4 more per sheet — the minimal extra cost provides insurance against future problems. In my professional opinion, use moisture-resistant board throughout any bathroom, toilet room, or utility room. The only exception would be a large bathroom with zoned sections, where areas more than 2 metres from any water source might use standard board if ventilation is excellent.

What’s the difference between green board and blue board?h3>

Green board refers to moisture-resistant plasterboard with water-repellent additives in the gypsum core and treated paper facing. Blue board typically refers to soundproof or acoustic plasterboard, which has higher density for noise reduction but isn’t necessarily moisture-resistant. Always check the manufacturer’s specifications — the colour alone doesn’t guarantee moisture resistance. Look for products specifically marked as “moisture-resistant” or “MR board” conforming to BS EN 520 Type H1 classification.

How long must I wait before tiling over cement render in a shower?

The safe minimum is 7 days for modern rapid-setting renders like Limelite Tough Coat, and 14-21 days for traditional sand and cement render. This allows sufficient curing and moisture release. The exact time depends on thickness, temperature, and ventilation. A simple test: the render should be uniform in colour with no dark (damp) patches remaining. When in doubt, wait longer — tiling too early causes more problems than waiting an extra week. I’ve seen tile installations fail because someone tiled after 5 days instead of 7 to meet a deadline. Don’t let anyone pressure you into rushing this stage.

Is tanking really necessary if I’m using waterproof backer boards?

In shower cubicles and wet rooms (Zone 0 and Zone 1), yes, tanking provides essential additional protection. While backer boards resist water penetration, the joints between boards create potential weak points. Tanking membranes create a continuous waterproof layer across the entire surface, including joints. Think of it as a belt-and-braces approach. For areas outside Zone 1 (general bathroom walls), tanking isn’t essential if you’re using proper moisture-resistant boards and won’t be tiling. However, for tiled shower areas, I always tank — the £50-80 extra cost is cheap insurance against water damage to the structure behind.

Can I plaster directly onto brick walls in a bathroom?

Yes, and in fact brick or blockwork provides an excellent substrate for bathroom plastering. Use a cement-based render rather than gypsum plaster. The typical approach: apply a 10-12mm scratch coat of sand and cement (4:1 ratio), score it while still wet, allow to cure for 48 hours, then apply an 8-10mm finishing coat. Alternatively, use a single-coat product like Limelite Tough Coat up to 25mm thickness. The masonry substrate is inherently more moisture-resistant than timber stud walls, making it actually preferable for wet areas. Ensure the brickwork is sound and repoint any loose mortar joints before plastering.

What causes plaster to bubble or blow in bathrooms?

Bubbling or “blowing” plaster in bathrooms has several causes:

• Wrong plaster type: Gypsum plaster absorbs moisture, swells, and loses adhesion
• Poor substrate preparation: Dust, grease, or paint preventing proper adhesion
• Application too thick: Thick layers trap moisture and create internal stresses
• Insufficient drying between coats: Moisture trapped between layers
• Lack of bonding agent: Essential on smooth surfaces like concrete blocks or painted surfaces
• Rising damp or leaks: Water entering from behind the plaster through damp walls or hidden leaks

Prevention requires proper material selection (cement-based in wet areas), thorough surface preparation, appropriate bonding agents, and addressing any underlying damp issues. If you’re experiencing these problems, our article on repairing cracked plaster walls covers remedial techniques, though bathroom failures often require complete replacement rather than patch repairs.

Final Recommendations: Best Practice for 2026

Based on current materials, regulations, and industry best practice, here’s my recommended approach for different bathroom scenarios:

For budget bathroom refreshes (under £3,000):

• Moisture-resistant plasterboard throughout
• Tile backer boards in shower area only (Hardie Backer or similar)
• Single-coat tanking membrane in shower zone
• Paint walls outside wet zones with bathroom-specific paint

For mid-range renovations (£5,000-10,000):

• Moisture-resistant plasterboard in dry zones
• Premium backer boards (Marmox/Wedi) throughout wet zones
• Full tanking system in shower and bath zones
• Quality tiles with epoxy grout in wet areas

For high-end wet rooms and luxury bathrooms (£10,000+):

• Structural waterproof membrane throughout floor and walls
• Premium insulated backer boards for thermal efficiency
• Underfloor heating with tanking overlay
• Large-format tiles with minimal grout lines
• Continuous mechanical ventilation with heat recovery

Whatever your budget, never compromise on moisture protection. Cutting corners on materials to save £100-200 will cost you £2,000-5,000 in remedial work within a few years. The bathroom is the most moisture-intensive room in your home — it deserves materials specified for the task.

For more information about general plastering techniques and materials, visit our comprehensive guide on types of plaster explained, which covers the full range of plastering products and their appropriate applications.