Behind every long-lasting driveway, pristine sports pitch, or sustainable drainage system lies an unsung hero: a high-performance sub-base. While the surface finish gets all the credit, it’s the aggregate underneath that does the heavy lifting – providing structural stability, bearing heavy traffic loads and managing groundwater.
Choosing the wrong aggregate for your project isn’t just a minor oversight; it can quickly lead to costly issues such as surface flooding, water pooling, frost heave and total structural failure.
Whether you’re planning a permeable paving installation, an equestrian arena or a commercial civil engineering build, selecting the correct sub-base is critical to long-term success. In this guide, we’ll explore what Type 3 aggregate is, examine how it compares to traditional MOT Type 1, outline its key applications and explain why it has become the go-to choice for meeting modern Sustainable Drainage Systems (SuDS) standards.
Designed specifically for free-draining and permeable applications, Type 3 (often referred to as Clause 805 or MOT Type 3) is a crushed primary aggregate engineered to offer the perfect balance of load-bearing strength and superior drainage. Unlike standard sub-bases that trap water, Type 3 features a reduced proportion of fine particles, creating open voids that allow surface water to filter through quickly and naturally into the ground below.
Specification Compliance
Type 3 aggregate is fully compliant with the Department for Transport’s Specification for Highway Works, Clause 805 (SHW 805). This national standard guarantees that the material meets precise criteria regarding strength, durability, and particle size distribution. When a project demands a certified, high-spec sub-base layer, specifying Clause 805 Type 3 ensures full compliance with local authority and engineering requirements.
Grading & Composition
Typically produced from crushed primary rock such as hard limestone or granite, Type 3 aggregate is supplied in coarse gradings, most commonly 0/40mm or 0/55mm. This means the material consists of a mixture of angular crushed stones ranging from larger 40mm or 55mm pieces down to smaller crushed fragments. The angular shape of the crushed rock is vital: it allows the stones to interlock firmly when compacted, creating a dense, stable bed capable of supporting heavy surface loads.
The “Reduced Fines” Feature
What truly sets Type 3 apart from other traditional sub-bases is its reduced fines content. In aggregate terminology, “fines” refer to the tiny dust and sand particles that fill the gaps between larger stones. While standard sub-bases rely on high levels of dust to lock solid, Type 3 is screened to remove the vast majority of these fine particles. By eliminating the excess dust, Type 3 avoids the risk of fine material washing away, clogging geotextile membranes, or silting up surrounding drainage pipes.
High Load-Bearing Yet Permeable
By combining crushed angular stone with reduced fines, Type 3 aggregate achieves what seems like a contradiction: a sub-base that is extremely tough yet highly porous. When rolled and compacted, the larger angular stones lock together to form a heavy-duty, load-bearing platform that won’t shift under vehicle or foot traffic. At the same time, the absence of fine dust leaves open voids throughout the compacted layer. These voids act as a natural network of channels, allowing surface water to drain through freely, preventing standing water and making Type 3 the ultimate sub-base for modern permeable installations.
Sustainable Drainage Systems (SuDS) & Permeable Paving: Used under permeable block paving, porous asphalt or gravel driveways to comply with UK planning regulations on water run-off.
Equestrian Menages & Arenas: Provides a firm, free-draining structural bed for horse arenas and gallops to keep surfaces mud-free year-round.
Sports & Leisure Facilities: Ideal sub-base layer under 3G artificial turf, tennis courts and golf course drainage zones.
Utility & Infrastructure Works: Protects surrounding drainage networks or geotextile membranes from being clogged by fine dust.
TJ Transport’s Type 3 Limestone – a primary quarried aggregate compliant with Clause 805 – is a great choice. With a 0/55mm grading, it is sold per tonne, with delivery available in 5-29 tonne loads. It can also be delivered as fast as the next day, depending on availability and your location. Input your postcode on our product page to get an accurate price for delivery to your location.
Find out more about our Type 3 Limestone and place your order today…
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