Concrete: Practical Tips, Materials & Common Issues for UK Home Projects

If you’re thinking about a new extension, a garden room, or fixing a cracked foundation, concrete is probably the first material that comes to mind. It’s strong, versatile, and used in almost every kind of building work. But not all concrete is the same, and using the wrong mix or skipping a simple step can lead to cracks, costly repairs, or a weak structure. Below we break down what you need to know before you pour, from picking the right mix to fixing problems after they appear.

Choosing the Right Concrete Mix

When you ask a supplier for concrete, they’ll give you a few numbers – strength grade, slump, and sometimes a brand name. For most home projects, a 25‑30 MPa (mega‑pascal) mix works fine. It’s strong enough for driveways, floors, and small foundations, while still being affordable.

Pay attention to the slump rating. A higher slump means the mix is wetter and easier to work with, but it can also be weaker. For a slab that needs to stay level, a slump of about 75‑100 mm is a good balance. If you’re pouring a deep footing, ask for a lower slump to avoid sagging.

Don’t forget additives. A small amount of waterproofing admixture can stop moisture from getting into the concrete later on, which helps avoid surface scaling and freeze‑thaw damage. Air‑entraining agents are also useful in colder regions of the UK; they create tiny bubbles that give the concrete a little give when it expands in winter.

Finally, always get a concrete delivery schedule that matches your work plan. Concrete starts to set after about an hour, so you need enough crew on site to spread, level, and finish the surface before it hardens.

Dealing with Cracks and Repairs

Even the best‑mixed concrete can develop cracks. The most common reasons are settlement, temperature changes, or shrinkage as the mix dries. A hair‑thin crack (less than 0.5 mm) is usually harmless – you can just seal it with a clear epoxy or cement‑based filler.

If you see a wider crack, measure it. In the UK, a crack wider than 3 mm in a foundation is a red flag. It could mean the ground is moving or the original build didn’t have enough reinforcement. In that case, call a structural engineer before you try a DIY fix.

For DIY repair of a moderate crack (up to 5 mm wide), clean the area, apply a hydraulic cement mix, and press it in firmly. Hydraulic cement expands as it sets, creating a tight seal that stops water infiltration. Once it’s dry, brush off excess and apply a concrete resurfacer for a smooth finish.

Preventing cracks in the first place is easier than fixing them later. Make sure your sub‑base is well‑compacted, use proper reinforcement (like steel mesh or rebar), and keep the concrete moist for at least the first 48 hours – covering it with a plastic sheet works well.

These practical steps cover most of what homeowners need to know about concrete on a typical UK renovation or extension. Browse the related articles on our site for deeper dives into foundation crack sizes, the best cement for repairs, and raw materials you might need for bigger builds. With the right mix, careful pouring, and timely fixes, your concrete work will stay solid for years to come.