Block Paving Installation: Sub-Base Depth, Sand Bedding, Soldier Courses, Cutting and Joint Sealing

Summary

Block paving is one of the most common residential driveway surfaces in the UK, and getting the construction right from sub-base upwards is what separates a driveway that lasts 20+ years from one that starts settling and rocking within five years. The three most common failure points are: inadequate sub-base depth, poor edge restraint (which allows the whole surface to spread), and using the wrong sand fill in joints.

The principles are straightforward but unforgiving if shortcuts are taken. Block paving is a flexible pavement — unlike concrete or tarmac, it has no structural rigidity and depends entirely on confinement and compaction to function. The edge restraint must be installed and cured before the main blocks, the sub-base must be compacted in layers, and the bedding sand must never be compacted before blocks are laid (only after, by vibration through the blocks).

For a tradesperson, understanding the BS 7533 specification means you can justify your method and specification to customers, defend your work against complaints, and produce a surface that genuinely lasts.

Key Facts

• BS 7533-3:2005 — British Standard for pavements using clay, natural stone, or concrete pavers; design for residential driveways and footways
• Sub-base minimum depth — 100mm Type 1 granular sub-base for standard residential driveway (vehicle use); 150mm on weak or made-up ground
• Type 1 sub-base — Recycled or primary crushed aggregate, well-graded, maximum particle size 37.5mm; must be compacted in layers not exceeding 200mm
• Bedding sand — 40–50mm sharp sand (grit sand); not building sand (too fine, retains moisture, causes settlement)
• Block depth — Minimum 50mm for residential block paving; 60mm for commercial/light HGV use; 80mm for heavy commercial
• Laying pattern — Herringbone (45° or 90°) gives best interlock; stack bond (grid) gives least interlock and is generally not used for driveways
• Soldier course — Perimeter restraint course of blocks laid soldiers (on edge perpendicular to main blocks) or sappers (on edge parallel); haunched in concrete min C20 before interior blocks
• Concrete haunching — 100mm wide × 75mm deep minimum at each edge; must cure before vibrating main surface
• Kiln-dried sand joints — Swept in dry, vibrated down; prevents block rocking; sealant can be applied afterwards but must not trap moisture
• Vibrating plate compactor — Required for bedding and jointing; minimum 75kg plate; use rubber mat to protect block faces
• Falls — Minimum 1:80 (1.25%) fall away from buildings; 1:60 preferred on smooth blocks
• Permeable block paving — Jointing must use 2–5mm grit or permeable grout, not kiln-dried sand, to maintain SuDS compliance
• DPC clearance — Finished paving level must be minimum 150mm below damp proof course (DPC) of adjacent building
• Compaction before bedding — Sub-base must be fully compacted before bedding sand is screeded; never compact bedding sand alone

Quick Reference Table

Detailed Guidance

Sub-Base Construction

Excavation — Calculate total excavation depth as: finished level + block depth + bedding sand + sub-base + geotextile (if used). A standard residential driveway often requires 250–300mm of excavation from finished level.

Geotextile — On clay or silty soils, lay a woven separation geotextile over the formation (the excavated ground level) before placing sub-base. This prevents sub-base aggregate mixing with fine-grained soil under traffic loading. Use a geotextile with adequate CBR (California Bearing Ratio) improvement properties. Non-woven geotextiles can blind and impair drainage on permeable installations.

Sub-base placement — Place Type 1 in layers not exceeding 200mm. Compact each layer with a vibrating roller (at least 1-tonne dead weight or equivalent plate compactor with forward and reverse passes). For small residential jobs, a 300–400kg vibrating plate is typically used, but must make multiple passes and overlapping runs.

Setting levels — Compact sub-base to finished design level minus block depth minus bedding sand depth. For 50mm blocks with 40mm sand bedding, set the sub-base to 90mm below finished surface level.

Edging and Restraint Installation

Edge restraints must be installed before the main field of blocks. Without them, the blocks will gradually spread under traffic loading, gaps will open, and the surface will become uneven.

Options:

• Concrete haunching — lay perimeter soldier/sapper course first, then haunch the outside edge with C20 or stronger concrete; simple, economical
• Proprietary plastic or metal edge restraints — flexible edge systems (e.g. Brickset, EcoEdge) hammered into sub-base; better for curves; no concrete curing time needed but less robust under vehicle tyres
• Raised kerbs — precast concrete kerbs (BS EN 1340) haunched in concrete; gives a formal edge profile; commonly used adjacent to roads and at driveway entrances

Haunching specification: Concrete must be placed against the outside face of the perimeter blocks, extending at least 100mm wide and 75mm deep. Allow minimum 24 hours curing before vibrating the main surface with a plate compactor.

Screeding Bedding Sand

Material — Sharp sand (also called grit sand or coarse sand) with particles 2–5mm. DO NOT use building sand (fine, sticky, high clay content — causes plastic deformation under load). Some installers use a 50:50 mix of sharp sand and crushed limestone fines, which gives good interlock. Washed angular grit is the best choice.

Screeding — Run two parallel screed rails at the correct height and use a screed board to pull the sand level. Bedding sand should be 40–50mm depth before blocks are laid.

CRITICAL: Do not compact or tamp bedding sand before laying blocks. Any pre-compaction creates voids under block edges. The sand is compacted only by vibrating through the blocks once they are laid.

Moisture — Sand should be damp but not wet. Dry sand is hard to screed; wet sand will shift. A good guide: squeeze a handful — it should hold shape without dripping.

Laying Pattern

Herringbone (45° or 90°) — recommended for driveways. Blocks interlock in two directions, distributing vertical loads and resisting horizontal spreading. 45° herringbone gives the most attractive appearance with fewer off-cuts on straight boundaries; 90° herringbone is easier to set out.

Basket weave and running bond — decorative patterns with lower interlock; suitable for patios but not recommended for driveways subject to regular vehicle loading.

Setting out — Snap chalk lines from a datum at 45° or 90° to the house/boundary. Always start from a fixed line and work outward. Cut blocks at boundaries last.

Cutting

Angle grinder with a diamond disc cuts individual blocks cleanly. A hydraulic block splitter (guillotine) is faster for repetitive straight cuts and produces a cleaner natural break. For curved cuts (around manhole covers, sweeping curves), mark and cut with diamond disc.

Safety — Block cutting produces respirable silica dust (RCS). Under COSHH Regulations 2002, a risk assessment is required. Always use:

• Water suppression (wet cutting preferred) OR
• H-class vacuum extraction with dust-shrouded cutter
• FFP3 dust mask as minimum if using dry cutting
• Do not dry cut without controls — RCS WEL is 0.1 mg/m³ (8-hour TWA)

Vibrating and Joint Filling

First pass — Once blocks are laid across the main area, dry sweep kiln-dried jointing sand over the surface and vibrate with a 75kg+ plate compactor (rubber or polyurethane pad attached to avoid scuffing). Work in overlapping passes. The vibration compacts the bedding sand and drives kiln-dried sand into joints.

Top up joints — After first vibration, joints may have settled. Sweep in more kiln-dried sand and re-vibrate. Repeat until joints are full.

Keep blocks dry — Kiln-dried sand will not flow into joints if blocks are wet. Work in dry conditions; if blocks are wet, allow to dry before sweeping sand.

Permeable paving — For permeable installations, use 2–5mm granite or limestone grit as jointing material. This maintains the void structure. Never use kiln-dried sand for permeable paving — it reduces permeability.

Joint Sealers

Optional but popular with customers. Benefits: prevents weed growth, ants, and joint erosion. Types:

• Polymeric jointing sand (e.g. Gator, EasyJoint) — contains a binder that activates with water; highly effective at locking joints
• Liquid joint sealers — applied after normal jointing; penetrates and binds
• Full block sealer — protects block face as well as joints; changes appearance (some add gloss)

Note: Sealers trap moisture if applied too early. Allow new blocks to weather for at least one season before applying full block sealers.

Frequently Asked Questions

Why is my block paving sinking in the middle?

Almost always a sub-base issue: either insufficient depth, or the sub-base was not properly compacted in layers. If there's a soft spot under the sub-base (old tree root, void, made-ground), that will also cause localised settlement. Repair: lift blocks, excavate, improve sub-base, re-lay bedding sand, re-lay blocks.

Can I lay block paving straight onto existing concrete?

Yes, with important conditions: the existing concrete must be structurally sound (no cracking, heave, or active settlement), clean, and at an appropriate level. Lay 25–30mm of sharp sand bedding on the concrete. The concrete provides the structural base so sub-base excavation is avoided. Check that the finished level will still be 150mm below DPC.

How do I stop weeds growing through block paving?

Weeds grow in the joints, not through the blocks. Full joint filling with kiln-dried sand prevents weed establishment. Polymeric sand or a liquid joint stabiliser is more effective for the long term. A geomembrane weed barrier between sub-base and bedding sand provides an additional barrier but does not replace joint filling.

What's the maximum slope for block paving?

Practically, up to 1:10 (10%) is achievable with block paving. Above this, the blocks tend to creep downhill under vehicle braking loads. For slopes above 1:8, consider bound alternatives (tarmac, resin bound) or incorporate retaining features. Minimum slope for drainage is 1:80 (1.25%).

Regulations & Standards

• BS 7533-3:2005 — Pavements constructed with clay, natural stone or concrete pavers: Part 3 — code of practice for laying precast concrete paving blocks and clay pavers for flexible pavements

• BS EN 1338:2003 — Concrete paving blocks; requirements and test methods; the product standard for concrete blocks used in driveways

• BS EN 1344:2002 — Clay pavers; requirements and test methods; the product standard for clay/brick paving

• COSHH Regulations 2002 — Control of silica dust from block cutting; requires dust risk assessment

• Building Regulations Part H — Drainage of buildings; relevant for driveway drainage to sewer or soakaway connections

• Town and Country Planning (GPDO) 2008 — Permitted development rules for driveways; 5m² impermeable limit for front gardens (see suds regulations driveways)

• Interpave: Block Paving Guide — Interpave (Precast Concrete Paving and Kerb Association) technical guides

• BS 7533-3:2005 via BSI — British Standard for pavement construction with precast paving blocks

• HSE: Silica Dust in Construction — guidance on RCS exposure control

• suds regulations driveways — planning permission requirements for impermeable driveways over 5m²

• paving edging restraints — edge restraint options and concrete haunching specification

• paving near dpc level — finished paving level requirements relative to damp proof course

• block paving lifting repair — repair methodology for settled or damaged block paving