Concrete is a fundamental material for many DIY projects, whether you’re building a patio, setting fence posts, or constructing garden paths. Understanding the difference between cement and concrete is essential. Cement is a binding agent, while concrete is a mix of cement, sand, aggregate (gravel or crushed stone), and water.
Concrete Ratings and Uses
Concrete in New Zealand is rated based on its strength, measured in megapascals (MPa). Common ratings for DIY jobs include:
- 20 MPa – Suitable for patios, paths, and non-load-bearing surfaces.
- 25 MPa – Ideal for driveways and light structural work.
- 30 MPa – Used for structural walls and heavier load-bearing elements.
Mixing Concrete
To make concrete, you can either gather the materials separately or use a convenient option known as builders mix, a pre-mixed combination of sand and aggregate. The most common mixing ratio for DIY projects is:
- 5 or 6 parts builders mix
- 1 part cement
- Water (added gradually)
The water amount is crucial—too much can weaken the mix, while too little makes it difficult to work with. Aim for a thick but pourable consistency.
Mixing Methods
Depending on the size of your project, you have several options for mixing concrete:
- For small jobs (like setting posts), mix concrete in a wheelbarrow using a shovel. This is a quick and manageable method for small quantities.
- For larger DIY projects (like driveways or patios), using a concrete mixer is more efficient. You can rent one from most equipment hire shops, ensuring a smoother, more consistent mix.
- For very large projects, it’s more practical to order ready-mixed concrete from a supplier. Concrete trucks can deliver up to 6 cubic metres per load, ensuring you have enough material for extensive projects like house foundations or large slabs.
Strength and Waiting Times
Concrete gains strength over time, so proper curing is essential:
- Initial set time: 24-48 hours (depending on weather conditions)
- Full strength: Reached after 28 days
For small projects, you can walk on the concrete after 24-48 hours, but wait a full week before applying heavy loads, especially for structural applications.
With the right mix and method, your DIY concrete project will be durable and long-lasting, whether it’s a simple garden path or a new driveway!