Sub-base Preparation — Excavation, Membranes & Compaction
A durable patio, driveway or slab starts with a well-built sub-base. We handle the full process: excavating to the right depth, assessing and improving the subgrade, installing geotextiles where needed, selecting the correct aggregate and compacting it in controlled layers to laser-set falls. Edges are contained so the stone can’t migrate, drainage is considered from the outset, and surfaces are left ready for the next trade. The result is a firm, even platform that won’t pump, rut or settle—so your finished surface stays level and looks good for years.
Excavation & Subgrade
We strip topsoil and soft spots to reach competent ground, protecting the formation from rain and trafficking. The subgrade is checked for consistency, moisture and bearing; weak areas are excavated and replaced or stabilised. We confirm design depths against finished levels so thresholds, steps and manhole covers align. Access is planned to keep sites tidy and safe, with arisings stockpiled for reuse where suitable or removed promptly to avoid contamination. Before any stone goes down, we proof-roll or plate test to confirm the formation is firm, even and ready to build upon.
Depths, Edging & Disposal
Depths are set from a fixed datum so the finished build-up (membranes, sub-base, bedding and surface) meets the correct height at doors, paths and kerbs. We install edge restraints early—kerbs with concrete haunching, steel or sleeper edging—so the sub-base is locked in place. Waste is segregated; soils and rubble are carted with duty-of-care paperwork, and reusable clean hardcore is identified where appropriate. This disciplined approach keeps the excavation neat, controls costs and ensures the new construction can’t creep or spread once traffic is introduced.
Geotextiles & Separation
Membranes stop the sub-base stone from punching into the soil and prevent fines from migrating up into the aggregate. On stable ground we use a non-woven separation layer; on marginal or wet subgrades we can specify a stronger, woven product or a composite that adds reinforcement. Overlaps, orientations and trench laps are detailed so there are no weak seams. Penetrations for drains or ducts are sealed neatly, and edges are turned up against kerbs to form a cradle. The result is a clean, separated build-up that drains and compacts as intended.
Stabilising Weak Subgrades
If the formation is soft or waterlogged, we have options: increase excavation and backfill with well-graded stone, introduce a stabilising geotextile/geogrid, or lime/cement-improve the top layer (as appropriate). We proof-roll between steps to verify the improvement, and only proceed once the subgrade resists rutting. This ensures the sub-base compacts uniformly, avoids differential settlement and protects finishes from reflective cracking or rocking slabs.
Aggregate Selection
Choosing the right stone is critical. For most patios and conventional drives, a well-graded, crushed aggregate such as Type 1 MOT gives dense, interlocking compaction. Where a permeable build-up is required (SUDS), open-graded Type 3 is specified to allow water to pass through to the drainage layer. In light-duty paths or as regulating layers, quality scalpings can be used sensibly. We’ll match the material to loading, drainage strategy and surface choice so performance and cost are balanced.
Type 1 MOT, Type 3 (Permeable) & Scalpings
Type 1 MOT creates a tight, stable base that resists rutting—ideal beneath slabs, resin, tarmac and block paving. Type 3’s larger voids support permeable surfaces and rapid drainage, often combined with soakaways or attenuation crates. Scalpings are suitable for temporary works or minor regulating layers where dense interlock isn’t essential. We check moisture content before placement and reject contaminated loads, ensuring consistent compaction and long-term stability.
Placement & Compaction
Sub-base is placed in controlled layers and compacted progressively so density is achieved through the full depth, not just the top. We spread evenly, avoid segregation and maintain moisture within the optimal range for compaction. Each layer is compacted with the appropriate plant (roller or heavy plate) and tested visually and by feel; where specified we can verify with a Clegg hammer or plate test. Building in thin lifts prevents later settlement and gives a solid, quiet platform for bedding or asphalt.
Layer Thickness & Roller/Plate Passes
Typical lifts are 75–100 mm for rollers or 50–75 mm for plate compactors, adjusted to aggregate size and site conditions. We run systematic, overlapping passes—edge to edge, then at right angles—until refusal is reached and the surface “rings” tight. High spots are trimmed, low spots are corrected with additional material (not fines), and we never “make up” levels with bedding. This methodical approach delivers consistent density and a flat plane ready for accurate laying.
Levels & Falls
From the first scrape we’re working to finished levels. Using lasers and straightedges, we build the sub-base to the same planes and falls the surface will follow, so bedding layers remain thin and uniform. Typical patio falls are set around 1:60–1:80 towards channels, gullies or garden drainage, adjusted to surface type and site constraints. Drive gradients and thresholds are coordinated so water sheds away from buildings and pooling is avoided. Accurate levels at this stage make laying faster and finishes noticeably sharper.
Laser Set-out & Drainage
We set control pins and rails to a fixed datum, checking frequently as layers go in. Drainage points—ACO channels, gully pots, inspection covers and soakaway locations—are positioned and boxed neatly, with the sub-base trimmed to receive them. Interfaces to walls and edging are struck straight and true so perimeters look measured, not guessed. With levels confirmed at sub-base, the next trade can achieve perfect lines without over-bedding or last-minute compromises.
Why Choose DM Jones Contractors
- ✓ Proper ground assessment, separation membranes and stabilisation where needed.
- ✓ Correct aggregates selected for loading and drainage (Type 1 / Type 3).
- ✓ Controlled lift thickness and thorough compaction for lasting stability.
- ✓ Laser-set levels and falls that match the final finish—no over-bedding.
- ✓ Edge restraints installed early to lock the build-up in place.
- ✓ Clean sites, compliant waste disposal and tidy interfaces for the next trade.
- ✓ Clear communication, fair pricing and local references.
Book Sub-base Works
Send a photo, rough sizes and the finish you’re planning (slabs, blocks, resin, tarmac). We’ll confirm depths, aggregates and falls, advise on drainage and edging, and provide a clear, itemised quotation with a realistic programme. If you already have drawings, share them and we’ll build to spec and leave the site ready for the next trade.
