Pour me a slab

Pour me a slab

In last week’s blog we talked about cutting concrete, and mentioned a few tips on how to make cutting concrete a bit easier. Our discussion raised a few points about pouring concrete, particularly making something simple such as a concrete path or a pad for firewood or rubbish bins. A few hours work can certainly help in tidying up the backyard and reducing the risk of mud getting trampled into the house. So here’s our tips for laying a concrete path

1. Excavate to the correct depth

Depending on the final use of the concrete pad or pathway, you’ll probably need to remove about 150 mm of topsoil in order to create a stable foundation. It pays to check the local regulations first.

2.Lay the foundation

Again depending on the use of the pad or pathway and the relevant building requirements, you’ll need to add back some gravel to create a stable base. This should usually be about 75 mm thick (but please check first) and well compacted. Our smaller plate compactors are ideal for these sorts of jobs. Add a small amount of sand to fill in any holes and provide a smooth base. You may also want to place some steel mesh, elevated 20 mm or so, to provide extra strength to the finished slab.

3.Nail the boxing

Using something like 25mm x 100 mm timber, nail together the desired boxing for the concrete. The nails should not be hammered home, so that the boards can be easily separated once the concrete has been set. We also had someone suggest we wipe down the boards with some old engine oil to prevent the concrete sticking to the timber.

4.Find your level

With the nailed frame in place, carefully lower it into place and check that all the corners are square and the top faces of the boxing are level.

5.Peg into place

Perhaps using some of the boxing off cuts, knock the pegs into place, ensuring the tops of the pegs are below the boxing. This will make ‘floating’ off the excess concrete easier and quicker. Use some 50 mm screws to tie the pegs to the boxing, as these are easier to undo once the concrete has set. Check the levels and the lines again.

6.Prepare for the concrete

Before pouring in the concrete, lightly spray the surface with water. Bone-dry foundations will tend to draw the water out of the concrete, resulting in quicker setting of some parts of the concrete and possible cracking. Allowing the concrete to set evenly can reduce the risk of cracks appearing in the final slab.

7. Box to the Pour

It’s not wise to float off two separate pours of concrete, as there is a risk of a distinct crack or mark appearing. If you are pouring a large amount of concrete requiring more than one truck load or mixing your own, one wheelbarrow at a time, it’s often better to box up one section per pour so that you float off the correct section of concrete. For instance, if you are mixing your own concrete in a concrete mixer, it may be best to box up alternative 1.0m sections of a pathway and fill these (and float them off) on day one, and then complete the remaining sections a day or two later.

8.Use the right floats

Having got the right size screed to level off the concrete, you can then work the concrete to achieve the final finish. Steel floats are great for moving concrete around and working the mix into all the small gaps. However steel floats also tend to bring the large stones in the aggregate to the top. Wooden or magnesium floats are great for bring the sand to the top, but also sending the aggregate to the bottom, providing a bit more strength. As the concrete starts to set, a quick brush with a broom can help provide a slip resistant surface.

Remember to have everything prepared and all the tools available  before you start pouring. You’ll only have a short period of time during which the concrete is manageable, so don’t try and pour too much too quickly. We’d be interested to hear your tips for pouring concrete so please feel free to add them in the comments section.

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