For any tile supplier, understanding and communicating the importance of correct grout line width is essential. Grout width, also known as grout line or grout gap, isn’t just an aesthetic choice—it’s a key factor in creating durable and visually appealing tile installations. Although professional tilers and DIY customers are often highly knowledgeable, British Standards such as the BS 5385-1 can change recommendations. By staying up-to-date with the latest guidelines, our customers can confidently advise on grout widths, substrate options, and industry trends.
This useful guide explores the factors influencing grout width and how the latest standards can help your customers achieve professional, long-lasting results.
1. Why Grout Width Matters
Grout width, or the gap between tiles, serves more than just an aesthetic function. It provides structural integrity by allowing for thermal expansion, substrate movement, and size variations among tiles. Grout also acts as a barrier against moisture, dust, and debris, particularly important in high-traffic or wet areas.
In recent years, there’s been a shift towards smaller grout widths, as larger tile formats have become popular. This trend, along with updated tiling standards, emphasises the importance of correct grout width in achieving a seamless, cohesive look that withstands daily wear and tear.
2. Key Changes in BS 5385-1: 2018 for Tile Grout Widths
The 2018 revision of BS 5385-1 introduced significant changes that affect grout width recommendations, substrate materials, and tile placement methods, with a strong focus on quality, longevity, and ease of maintenance:
Elimination of Plywood as a Suitable Substrate: The new standard explicitly excludes plywood as a direct tiling substrate. Plywood’s tendency to absorb moisture and move with environmental changes can compromise the stability of tiles. Instead, tile backer boards are now recommended, as they offer greater stability, moisture resistance, and are more cost-effective given their compatibility with larger tile formats.
Updated Grout Widths for Large Tiles and Ceramic Panels: For large-format tiles and thin ceramic panels, BS 5385-1 now recommends minimum grout widths that correlate with the tile’s size:
Small Tiles (less than 600mm): A minimum grout width of 2mm is generally suitable, keeping lines visually tight without compromising function.
Large Format Tiles (600mm to 1200mm): Minimum 3mm grout width, especially for seamless floors, as the width allows for minor expansion.
Extra-Large Tiles (over 1200mm): Minimum 5mm grout width, which is now specified in the updated standard. For tiles larger than 80x80cm, a wider joint (2-3mm) prevents the tiles from cracking under environmental changes.
Enhanced Grout Requirements for High-Movement Areas: Wooden substrates and floors with movement require a grout width of 3-5mm, paired with flexible grout, to prevent cracking or displacement. The standard reinforces that flexible adhesives and grouts should always be used with wooden substrates to manage expansion and contraction.
3. Practical Considerations for Grout Width Based on Tile Type and Substrate
Several factors influence the choice of grout width, including the type of tile, its dimensions, and the substrate it’s applied to.
Rectified vs. Non-Rectified Tiles
- Rectified Tiles: With machine-cut edges, rectified tiles allow for tighter grout widths (1-3mm) for a seamless finish.
- Non-Rectified Tiles: Tiles with irregular or “wobbly” edges require a slightly larger gap (3-5mm) to accommodate these natural variations and maintain a uniform appearance.
Wall vs. Floor Tiles
- Wall Tiles: Smaller grout lines (1-2mm) are often preferred for walls, especially when using rectified tiles. However, a small grout joint—even as narrow as 1mm—is recommended to prevent water infiltration.
- Floor Tiles: Floors experience more movement and benefit from wider grout lines (typically 2-5mm). In wet rooms, a larger grout joint (4-6mm) can help manage slopes toward a drain while supporting the stability of the installation.
Underfloor Heating
Joints in tiles installed over underfloor heating systems should be at least 3mm wide, as this allows for expansion and contraction with temperature changes.
Wet Rooms and Shower Areas
Larger grout widths (4-6mm) help maintain tile stability, especially when directing tiles toward a drain. Anti-bacterial grout is recommended to reduce mould and moisture issues.
Tiles with Curved Edges
Certain kitchen wall tiles may have curved or uneven edges. For these, use a larger grout joint (3-6mm) to create a visually balanced look.
4. Choosing the Right Colour and Type of Grout
Colour and type are just as crucial as the width. Here’s how to make the best choice:
- Grout Colour: Light-coloured grouts are typically used with wall tiles, while floors benefit from darker shades like grey or charcoal to minimise visible staining. For dark tiles, dark grout can create a sleek, cohesive look.
- Grout Type:
- Cementitious Grout: Suitable for most wall and floor applications.
- Epoxy Grout: Ideal for areas prone to moisture, such as bathrooms or kitchens, due to its resistance to stains.
- Flexible Grout: Essential for floors and substrates with movement, as it can withstand expansion and contraction.
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5. Step-by-Step Guide to Achieving the Ideal Grout Width
Here’s how to ensure your customers achieve the correct grout width for their projects:
Step 1: Prepare the Substrate
A stable, clean, and dry substrate is essential. For areas exposed to moisture, recommend tile backer boards instead of plywood, which aligns with the updated BS 5385-1 standards.
Step 2: Plan and Dry-Lay Tiles
A trial layout of tiles and spacers helps visualise the final design, ensuring the right grout width is achieved.
Step 3: Use Spacers to Ensure Consistency
- Place spacers along each side of the tile to ensure even spacing.
- For larger tiles or uneven surfaces, tile levelling systems such as the Tylix kits are effective in preventing “lippage” and maintaining a consistent grout width.
Step 4: Incorporate Expansion Joints
Large areas require movement or expansion joints (typically every 5-8 meters) to allow for shifts in the floor. Our range of quality Qtrim movement joints prevent cracking and other stress-related issues, whilst maintaining high visual appeal.
Step 5: Remove Spacers and Apply Grout
Once adhesive is partially set, remove spacers before it fully cures, and then apply grout to the gaps. Flexible or epoxy grout is advised for areas with movement, underfloor heating, or high moisture.
Quantum Group – Optimising Grout Width for Professional Results
For wholesale tile suppliers in the UK and Ireland, staying informed about the latest industry standards is crucial. By offering retailers and tiling professionals clear guidance on grout widths, substrates, and best practices, you help ensure the highest-quality results in every project, enhance customer satisfaction, reduce callbacks, and reinforce your reputation as a trusted supplier. To find out more about the products included in this blog post, please contact our sales team for more information.