3 Bases and paving
Crushed stone with fines, compacted in thin layers, and the sand that paving sits on. This chapter is about load: what sits on top, and how much stone it needs under it. Patios, driveways (chapter 7) and garden paths (chapter 8) all build on these pages.
- 3.1Base for patios, paths and shedsFoot traffic, garden furniture and sheds. 100 mm of 0–16 or 0–32 mm crushed stone.
- 3.2Base for drivewaysCars and small vans on pavers. 150–225 mm of 0–32 mm crushed stone, compacted in layers.
- 3.3Sand bedding under paving25–30 mm of loose, sharp 0–4 mm sand, screeded on rails.
- 3.4Filling paving jointsDry 0–2 mm sand, swept in and vibrated until the joints are full.
The layers in this chapter compacted thickness
| Use | Base | Bedding | Top |
|---|---|---|---|
| Driveway (3.2) | 150–225 mm · 0–32 | 25–30 mm · 0–4 | Pavers |
| Patio, path, shed (3.1) | 100 mm · 0–16 or 0–32 | 25–30 mm · 0–4 | Slabs or pavers |
| Gravel path (7.3) | 100 mm · 0–32 | – | 75–100 mm · 0–8 |
| Gravel drive (7.3) | 150 mm · 0–32 | – | 75–100 mm · 0–16 |
Use the top of each range on soft, wet or clay ground. Sizes are in mm. Each page lists its sources.
Why the stone size matters
A 0– mix has every grain size down to dust. The small grains fill the gaps between the big ones, so the layer compacts dense and stays put. Clean stone without fines leaves open gaps. That is what drainage needs (chapter 6), but under paving the bedding sand washes down into the gaps, and on a gravel surface the stones roll aside under wheels.
Sources
- UFGS 32 14 13.13, Interlocking precast concrete unit paving (US Department of Defense unified facilities guide specification, 2019): a dense-graded base, within 10 mm under a 3 m straightedge; bedding sand screeded to an uncompacted average of 25 mm, left uncompacted and not walked on, and never used to fill low areas in the base; bedding sand to ASTM C33 with at most 1 % passing 0.075 mm; joint sand to ASTM C144 with at most 5 % passing 0.075 mm; joints 2–5 mm; gaps at edges at most 6 mm; at least three plate passes; no seating or joint filling within 1.5 m of an unrestrained edge; joint sand swept and vibrated until no more goes in; finished surface flush with or up to 6 mm above edges and drains
- Oregon State University Extension, 10-step guide to installing pavers: base of 4–6 in (100–150 mm) of 3/4-minus crushed rock, compacted in layers; bedding sand screeded to 1 in (25 mm); slope of 1 in per 4 ft (about 2 %)
- UK government (DCLG), Guidance on the permeable surfacing of front gardens: about 150 mm of sub-base, compacted before the surfacing is laid
- Bedford Borough Council, Appendix 11/1 Kerbs, footways and paved areas: block-paved light vehicle crossovers serving up to two houses: 65 mm blocks on 30 mm of 0/4 mm sand on 225 mm of Type 1 sub-base; sand layer at least 25 mm; joints filled with 0/2 mm sand
- UK Specification for Highway Works, Series 800, road pavements: unbound and bound mixtures (November 2021): Type 1 sub-base passes 100 % at 63 mm, 75–99 % at 31.5 mm, 43–81 % at 16 mm, 23–66 % at 8 mm, 12–53 % at 4 mm and 0–9 % at 0.063 mm; the part passing 0.425 mm must be non-plastic
- Gravel roads guidance (Skorseth, Western Transportation Institute): surface gravel at least 75 mm, all passing 25 mm, 8–15 % fines passing 0.075 mm, plasticity index 4–9; crown about 4 %
- EN 13285 Unbound mixtures: specifications. Mixtures are named 0–D, for example 0–32
- EN 13242 Aggregates for unbound and hydraulically bound materials
The guides above ask for a dense-graded base (UFGS 32 14 13.13: so the bedding sand is not lost into it) and for fines in a gravel surface.
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