Reinforcement Spacers Guide: How Many to Use

Getting the right number of spacers is just as important as choosing the right mesh or rebar. The correct spacers make sure your steel sits at the right cover, so your slab is stronger, more durable and compliant with standards such as BS 7973.

At Next Day Steel we stock three main spacer types for mesh and rebar:

• Plastic mesh spacers
• Wire snake spacers (deck spacers)
• Concrete spacers and castle mesh blocks

This guide shows you where each type is used and a simple way to calculate how many to order for your slab.

1. Quick Spacer Guide Per Mesh Sheet

For standard merchant mesh sheets 3.6 m x 2.0 m (common A142, A193, A252 etc.), a practical rule of thumb is:

For larger sheets or heavier duty industrial slabs, increase the number of spacers so that unsupported gaps between supports stay within roughly 600-800 mm.

2. Step-by-Step: Calculate Spacers for Your Slab

You can also work things out from slab area if you don't want to think in sheets.

Step 1 - Work Out Your Slab Area

Area = length x width in metres. Example: a 5 m x 4 m patio = 20 m².

Step 2 - Choose a Usage Rate

• Light domestic slabs (patios, paths, sheds): around 0.5 spacers per m²
• Driveways, garages, small commercial slabs: around 0.75 spacers per m²
• Heavy duty / industrial slabs, double mesh, poor ground: 1 spacer per m² or more, and/or tighter wire snake spacing

Step 3 - Multiply and Round Up

• Example 1 (domestic patio, plastic mesh spacers): 20 m² x 0.5 = 10 spacers - round up to the nearest pack
• Example 2 (small commercial slab, castle spacers): 50 m² x 0.75 = 37.5 - order 40-50 spacers
• Example 3 (industrial slab with wire snakes): 120 m² x 1 = 120 spacer points. Use this to set out lines of wire snakes at 600-800 mm centres and add a few extra for overlaps

We always recommend adding 10-15% extra to cover overlaps at joints and trimming on site.

3. When to Use Each Spacer Type

Plastic Mesh Spacers

Plastic mesh spacers are designed mainly for ground floor slabs and beams poured on top of a polythene DPM. The broad base helps prevent puncturing the membrane and keeps the mesh stable during walking and placing.

Typical applications:

• Domestic and light commercial ground slabs
• Internal floors with DPM
• Ground beams and edge thickenings

Usage guidance:

• Minimum 8 plastic mesh spacers per 3.6 x 2.0 m merchant mesh sheet
• Increase to 10-12 per sheet for heavier loads or poor sub-base
• Aim for spacers roughly 600-800 mm apart in a staggered pattern, not in straight lines

Shop Plastic Mesh Spacers

Wire Snake Spacers (Deck Spacers)

Wire snake spacers are continuous welded wire chairs, typically supplied in 2 m lengths, that provide a line of support across the slab. They are ideal where you want regular, continuous bearing under the mesh or between layers of mesh.

Typical applications:

• Slabs and decks where mesh needs continuous support
• Double-layer reinforcement where one layer is carried above another
• Situations where you want to avoid point loading on a DPM

Usage guidance:

• Each wire snake spacer is 2 m long
• Allow around 5 snakes per 3.6 x 2.0 m mesh sheet (laid perpendicular to the length of the sheet)
• Lay the snakes in parallel lines at approximately 600-800 mm centres
• For heavy duty / industrial slabs, reduce spacing to 400-600 mm centres to limit deflection

Shop Wire Snake Spacers

Concrete Spacers and Castle Mesh Blocks

Concrete spacers and castle mesh blocks are manufactured from high-strength concrete and are designed to comply with BS 7973, offering non-combustible, durable support that closely matches the concrete of the slab.

Typical applications:

• External slabs and pavements
• Heavy duty industrial floors
• Structural elements where fire resistance and long-term durability are critical

Castle mesh spacers:

• High-strength fibrous concrete with minimum 50 N/mm² strength
• Designed to BS 7973-1:2001
• Typically supplied with 40/50 mm cover options and 100 pieces per bag

Concrete clip-on spacers:

• Concrete body with integrated plastic clips for rebars or mesh, typically 8-16 mm diameter
• Four-point support to minimise contact with formwork and give even cover

Usage guidance (castle spacers):

• Standard slabs: 4-6 castle spacers per 3.6 x 2.0 m mesh sheet
• Heavy duty / external / industrial slabs: increase to 6-8 per sheet, maintaining support spacing below 800 mm
• Space in a staggered pattern across the sheet, avoiding long unsupported strips of mesh

Shop Concrete Castle Mesh Spacers | Shop Concrete Spacers with Plastic Clips

4. Practical Layout Tips on Site

Whatever spacer type you use, a few simple rules will help keep your steel at the correct cover:

• Place spacers on a reasonably firm and level base (blinded hardcore, insulation or shutter)
• Lay spacers in a staggered grid, not in straight lines, so the mesh is supported evenly
• Keep the distance between spacer supports within roughly 600-800 mm; reduce to 400-600 mm for heavy duty or industrial slabs
• Add extra spacers around laps, openings and edges where the mesh is more likely to move

Always follow the structural engineer's drawings and any project-specific specification. Where in doubt, use the guide numbers above as a minimum and increase spacer quantities for heavier loads, poor ground or complex reinforcement.

5. Need Help Choosing Spacers?

If you are unsure which spacers to use or how many to order, our team can help you size and specify the right solution for your project. Send us your drawing or quantities and we can advise on:

• Best spacer type for your application
• Approximate quantities for your slab area and mesh size
• Delivery options, including next-day where available

Call us: 020 8079 7719 | Email: sales@nextdaysteel.co.uk