C20 Concrete (20N) – Uses, Price & Delivery in London
C20 mix concrete is equivalent to a GEN3. C20 concrete mix holds a strength of 20 newtons after 28 days, and it sees frequent use in residential projects, with potential in select commercial uses as well. C20 mix is commonly used in a variety of projects, particularly on uneven surfaces. This characteristic adds to its adaptability, making it an easy-to-handle option suitable for various tasks.
C20 is commonly used for:
- Paving pathways and patios
- Creating bases for sheds and garages
- Constructing garage floors
- Making unreinforced strip footings
- Forming foundations for walls and single-storey structures
- Crafting internal floor slabs that will be concealed
Technically reviewed by Jim Taylor, Owner of Mixit Concrete, with over 42 years of concrete-industry experience.
C20 Volumetric Mix Design Ratios
When batching raw volumetric materials, a standard C20 structural grade follows an exact 1:2:4 mix ratio (1 part ordinary Portland cement to 2 parts clean sharp sand to 4 parts coarse 20mm aggregate). To guarantee a characteristic compressive strength class of 20 N/mm² at the full 28-day cure cycle, our computerised batch plants monitor material batch weights to maintain a minimum cement content parameter of 320kg per cubic metre (m³).
Maintaining this precise structural ratio ensures a dense, water-resistant matrix optimized for domestic slabs. It provides excellent resistance against surface wear and light vehicle traffic while preventing internal structural voids during the initial curing phase.
C20 Concrete – Delivered in London & Surrounding Areas
C20 concrete is one of the most widely used and trusted mixes in domestic construction. With a characteristic compressive strength of 20 N/mm², it offers a strong balance between durability, versatility, and cost‑effectiveness. It is significantly stronger than lighter mixes such as C10 and C15, making it suitable for a broader range of structural and semi‑structural applications around the home. Whether you’re building a driveway, laying a foundation for a garden room, or installing a robust floor slab, C20 provides the strength and reliability needed for long‑lasting results.
Homeowners and contractors often choose C20 because it sits at the sweet spot between affordability and performance. It is strong enough to support moderate loads, withstand regular foot and vehicle traffic, and resist weathering, yet it remains workable and easy to place. This makes C20 a go‑to choice for many domestic projects where durability is essential but heavy structural loads are not expected.
Use our C20 Concrete calculator to calculate & book instantly online.
C20 Technical Characteristics
Strength Rating
- 20 N/mm² compressive strength at 28 days.
- Often equivalent to GEN3 or ST2 in some UK specifications.
This strength level makes C20 suitable for a wide range of domestic foundations, slabs, and load‑bearing surfaces.
Workability
C20 is typically supplied with a medium slump, though higher slumps can be requested for easier placement. Its workability allows for:
- Smooth spreading
- Efficient compaction
- Reliable finishing
- Compatibility with reinforcement
C20 is workable enough for hand‑laying but strong enough for structural reliability.
Setting Time
Typical setting times include:
- Initial set: 2–3 hours
- Final set: 6–8 hours
- Full cure: 28 days
C20 can usually be built upon within 24–48 hours, depending on the application and weather.
Mix Composition
C20 contains:
- A higher cement content than C15
- Fine and coarse aggregates
- Water adjusted for slump
- Optional admixtures such as plasticisers, retarders, or accelerators
The mix is designed to provide dependable strength and durability.
Material Compatibility
C20 is compatible with:
- Steel reinforcement
- Damp‑proof membranes
- Concrete blocks and bricks
- Timber formwork
- Compacted MOT Type 1 sub‑bases
Avoid using C20 in:
- Sulphate‑rich soils without specialist cement
- Applications requiring very high compressive strength (C25+ recommended)
Customer Testimonials
“We used C20 for our new garage floor, and the results have been fantastic. The concrete set quickly, gave a perfectly smooth finish, and feels incredibly solid underfoot. Even with heavy tools and equipment, there’s been no movement or cracking. Highly recommended.”
How to use our concrete calculator to order
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Why Choose C20 Concrete?
C20 is the ideal choice when you need:
- A durable floor slab for garages or workshops
- A strong base for driveways and parking areas
- Foundations for small to medium domestic structures
- A reliable mix for patios, paths, and garden features
- A versatile concrete that balances strength and affordability
It is not suitable for:
- Heavy structural foundations
- Multi‑storey buildings
- High‑load industrial floors
- Applications requiring high compressive strength (C25–C40 recommended)
For those applications, higher grades such as C25, C30, C35 or C40 are more appropriate.
Engineering Specifications & Standard UK Code Equivalencies
For building contractors, structural engineers, and local authority inspectors, C20 concrete is specified under British Standard BS 8500-2 as the direct equivalent to GEN 3 (General Purpose Mix 3). This means it satisfies the design requirements for domestic floor slabs, internal garage bases without heavy loads, and outdoor paving structures in non-aggressive ground conditions (Design Chemical Class DC-1).
Choosing a C20 mix configuration provides the necessary structural support for domestic patios, workshop flooring, and lightweight concrete paths. If your site plans call out a GEN3 mix descriptor, this C20 formulation meets or exceeds those exact load criteria.
Slump and Workability Variations for On-Site Placement
Depending on how the mix is being placed on your site, the workability of the batch can be adjusted. For traditional wheelbarrow unloading or manual troweling on large surface areas, we supply a standard S2 slump. This provides a manageable consistency that finishes cleanly with a steel float or power trowel.
If you choose to use our ground line or boom concrete pump hire services, we adjust the batch parameters to an S3 slump. This increased fluid workability allows the concrete to glide through the pipelines smoothly, ensuring a consistent pour that reduces labor times on residential project sites.
Questions we are often asked about C20 Concrete
C20 is a medium-strength concrete commonly used for domestic foundations, garage floors, internal floor slabs, lightweight structural applications, and general construction work requiring good durability and strength.
(From: C20 Concrete)
Yes. C20 offers sufficient strength for many load-bearing tasks in residential construction, such as small foundations, floors, and footings. For heavier structural loads, higher grades like C25 or C30 are recommended.
(From: C20 Concrete)
C20 provides a reliable balance between strength, workability, and cost. It is strong enough for typical domestic foundations and floor slabs while being more economical than higher-grade mixes.
(From: C20 Concrete)
C20 reaches a compressive strength of around 20 N/mm² after 28 days, making it suitable for a wide range of medium-duty construction applications.
(From: C20 Concrete)
Yes. C20 can be pumped, and plasticisers or other admixtures may be added to improve flow and workability, especially for areas that are hard to access.
(From: C20 Concrete)
C20 typically begins to set within a few hours depending on temperature and site conditions. Light foot traffic is usually possible within 24–48 hours, but full curing takes approximately 28 days.
(From: C20 Concrete)
Yes. C20 is widely used because it provides a robust level of strength without the higher material costs of stronger mixes. It is ideal for residential and light commercial applications.
(From: C20 Concrete)
Technically reviewed by Jim Taylor
Jim Taylor, Owner of Mixit Concrete
This guide was technically reviewed by Jim Taylor, the owner of Mixit Concrete, who has over 42 years of experience in the concrete industry.
Drawing on decades of practical industry knowledge, Jim reviewed the information relating to C20 concrete strength, common applications, volume calculations, delivery requirements, concrete pumping and site preparation.
Jim oversees Mixit Concrete’s operations and has extensive first-hand experience supplying ready-mix concrete for domestic and commercial projects across London, Essex and Hertfordshire.
Technically reviewed: 16th June 2026
