What the grade numbers mean
Concrete mix grades like C25, C30 and C35 refer to the compressive strength of the concrete after 28 days, measured in Newtons per square millimetre (N/mm²). A C25 mix achieves a minimum of 25 N/mm², a C30 achieves 30 N/mm², and so on.
The higher the number, the stronger the concrete. Stronger isn't always better — the right mix is the one that matches what your project actually needs.
Common mixes and what they suit
C25 is the general-purpose mix for domestic work — paths, patios, driveway bases and non-structural slabs. C30 is typical for reinforced foundations, garage floors and light commercial slabs. C35 and C40 are used for heavier-duty applications — industrial floors, structural foundations and agricultural slabs.
Additives can modify the mix: plasticisers for workability, fibres for crack control, accelerators for cold weather, and air-entraining agents for freeze-thaw resistance.
Always follow the spec
If your structural engineer, building control officer or architect has specified a mix grade, use that grade — don't substitute down to save money. The spec is there for a reason.
If no spec exists, tell us what you're pouring and we'll advise on the right mix. With volumetric concrete, the mix is batched on site so we can adjust it if conditions change on the day.
Related services
Need concrete for your project? We supply volumetric concrete across South Wales, mixed fresh on site to the exact quantity you need. Request a quote or call 01495 820164.