If you are planning a project in Northwood and need concrete delivered, one of the first questions you will face is: which grade do you actually need? Getting the grade wrong can mean concrete that is too weak for the job, or paying for more strength than you need. This guide walks you through the four grades most commonly ordered for domestic and trade projects in the area, in plain language.
What Does a Concrete Grade Mean?
A concrete grade is a number that tells you how strong the concrete is. The number refers to the compressive strength in newtons per square millimetre, measured after the concrete has cured for 28 days. So C20 concrete has a compressive strength of 20 N/mm², C25 is 25 N/mm², and so on.
The higher the number, the stronger the mix. Stronger mixes use more cement, which is why they cost more. You do not always need the strongest mix available, but you do need the right one for what you are building.
For a fuller overview of concrete types and how they are classified, the Designing Buildings wiki on types of concrete is a useful reference.
The Four Grades Most Commonly Ordered in Northwood
The table below gives a quick overview before we go into detail on each one.
| Grade | Common Name | Typical Uses |
|---|---|---|
| C10 | GEN1 | Blinding layers, hard standings, infill |
| C20 | GEN3 | Shed bases, garden paths, internal slabs |
| C25 | ST2 | Driveways, strip footings, residential foundations |
| C30 | — | Structural slabs, heavy-duty foundations, commercial bases |
C10 Concrete
C10 concrete is the lightest mix in everyday use. It is often called blinding concrete, because one of its main jobs is to provide a clean, level surface to work on before the main structural pour goes in. You might use it as a base layer under a path, as infill beneath a step, or to firm up ground before laying slabs.
It is not designed to take heavy loads on its own, so it is not the right choice for a driveway or a load-bearing foundation. But for low-stress applications where you just need something solid and flat, C10 does the job well and costs less than higher grades.
C20 Concrete
C20 concrete is probably the most widely ordered grade for domestic projects. It sits in the middle of the general-purpose range, strong enough for most garden and light construction work, but not overspecified for everyday use.
Typical uses in Northwood include shed bases, garden path slabs, small patio areas, and internal floor slabs where the load is light. If you are putting up a garden building, a log cabin, or a greenhouse, C20 is usually the grade your supplier or builder will recommend.
C25 Concrete
C25 concrete is a step up in strength and is the standard choice for driveways and residential foundations. If you are laying a new driveway in Northwood, particularly one that will take a car or van on a regular basis, C25 is the minimum you should be using.
It is also suitable for strip footings on smaller domestic extensions and outbuildings. The extra strength compared to C20 means it handles frost and ground movement better over time, which matters in residential settings where the concrete is exposed to the elements all year round.
C30 Concrete
C30 concrete is used where the structural demands are higher. It is the right choice for reinforced slabs, more demanding foundations, retaining walls, and commercial or industrial bases.
For most straightforward domestic projects in Northwood, C30 is more than you need. But if a structural engineer has specified it, or you are working on a garage with a heavy vehicle in mind, or a basement slab, then C30 is the grade to order.
How the Concrete Is Mixed and Delivered
All mixes supplied to Northwood are produced fresh on site using a volumetric lorry. Unlike a traditional drum mixer that loads a pre-mixed batch at a plant and drives it to you, a volumetric lorry carries the raw materials separately and mixes the concrete at your site. This means you only pay for what you actually use, and the mix can be adjusted on the day if your requirements change.
For ready mix concrete in Northwood and the surrounding area, Base Concrete can supply all of the grades above, with lorries small enough to reach tighter residential roads and access points.
Not Sure How Much to Order?
If you know which grade you need but are not sure on the volume, use our concrete calculator to work out how much concrete you need based on the dimensions of your job. It takes a couple of minutes and gives you a cubic metre figure you can use when you call to book.
You can also browse our full range of ready mix concrete grades and services, or call our St Albans team directly on 01727 881979 to talk through your project.
