Aggregates, Sand & Pumice

GAP 20 (General All Passing 20mm) is a versatile crushed aggregate used for driveways, garden paths, sub-bases under paving and concrete, and as a foundation layer under outdoor entertaining areas. It compacts well because the mix of particle sizes – from fine dust up to 20mm – lock together under pressure to form a firm, stable surface. It’s the most commonly used residential aggregate product and a go-to for landscapers and DIY homeowners alike.

The number refers to the maximum particle size: GAP 20 contains particles up to 20mm, GAP 40 up to 40mm, and GAP 65 up to 65mm. GAP 20 is the standard choice for residential driveways, paths, and as a sub-base for paving. GAP 40 is used for heavier driveways, road bases, and foundations where load-bearing is more critical. GAP 65 is for heavy-duty sub-base work on commercial or civil projects. As a general rule: the bigger the project and the heavier the load, the larger the GAP grade you need.

For more information on this, check out our article Building, Landscaping, or Drainage? How to Choose the Right Aggregate

Calculate: Length (m) × Width (m) × Depth (m) = cubic metres. 

For a standard residential driveway, a two-layer approach is recommended: GAP 40 base at 100mm compacted depth, then GAP 20 surface at 50mm compacted depth – total 150mm. 

Example: A 20m × 3m driveway at 150mm = 20 × 3 × 0.15 = 9m³. 

Add 15% for compaction losses: 9 × 1.15 = approximately 10.5m³. 

Gammans’ minimum truck delivery is 2m³, most driveways will require at least one full truck load.

Try our handy Volume Calculator to help estimate the total volume of aggregate you’ll need.

For drainage applications – French drains, soakage pits, behind retaining walls – you need an open-graded aggregate that allows water to flow through freely without compacting or clogging. 

Gammans Drainage Aggregate (Drainage Metal) is specifically designed for this. Scoria and Drainage Pumice are also excellent options, particularly where weight is a consideration (both are significantly lighter than standard aggregate). Avoid using GAP products for drainage. They contain fine particles (fines) that compact and restrict water flow, which is the opposite of what you want.

Crusher dust is the fine material produced during the rock crushing process – particles ranging from dust up to approximately 7mm. It compacts to an extremely firm, smooth surface and is ideal for: paths and walkways where a hard-wearing finish is needed; bedding layers under pavers; compacted bases for sheds, garden structures, and light-use areas. It’s not recommended for driveways with regular vehicle traffic – use GAP 20 or GAP 40 for that. Crusher dust is also used as a gap-filling material between and under paving stones.

Both products are volcanic pumice, but graded for different applications. Horticultural Pumice is a fine grade used in potting mixes and to strike roots on cuttings and general propagation and also in garden beds to improve drainage and aeration around plant roots. It’s a key ingredient in many of Gammans’ custom potting mixes, ideal for cactus and succulents. Drainage Pumice is a coarser grade used for structural drainage applications – behind retaining walls, in soak pits, and as a lightweight alternative to drainage metal. If you’re improving soil or potting mix, use horticultural pumice. If you’re managing water drainage in a built structure, use drainage pumice.

For laying pavers, you need a coarse, sharp sand that won’t compact into a solid layer under the paving – this is sometimes called paving sand or bedding sand. Gammans stocks Paving Sand specifically for this application. Avoid using fine building sand or sandpit sand for paving – they are too fine, compact under load, and can cause pavers to sink unevenly over time. For the sub-base underneath the bedding sand, GAP 20 or crusher dust compacted to the correct depth will give you a stable, long-lasting result.

Both. Gammans aggregates are available in bags for smaller projects, and in bulk by truck delivery for larger orders or 1 tonne sling bags for the hard to reach areas. For smaller quantities – say, a trailer load for a garden path or small driveway – our free courtesy trailers are available for 2 hours when you purchase at the yard. Single axle trailers hold up to 1m³ of aggregate; double axle trailers hold more. Call ahead to check availability and confirm quantities before you head in: 027 548 1278.