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Extending a patio - need help with cement mix and hardcore

I’m extending an existing patio and have used old broken up bricks and roof tiles as hardcore to form a base. I have a lot of gravel in my garden (a lot of it used to be decked with the gravel underneath on top of a membrane) and was wondering if I could use some of this as well. Another question is getting concrete in the hole. How quickly will the cement set? And what’s the best way to get it spread out I’m going to rent a cement mixer which hopefully I can get in and out of my garden myself. In terms of the concrete mix I was told to use 1 part cement to 2 parts sand and 3 parts gravel. Is this correct? If not what is the best mix to use? I have a lot of gravel to use so I would add that and the sand separately and not buy a mixed bag.

Thanks in advance for any advice on this.

2 Answers from MyBuilder Groundworkers

Best Answer

You can buy ' ballast' which is ready mixed aggregate of sand and gravel. It's roughly 2 to 3 gravel to sand I think.
As for cement ratios a 5 to 1 I'd very strong but you can even go as lean a 8 to 1 ( they say)

So if I were you I would use the aggregate you have and the rubble as hardcore.
Keep the mix rich with cement and play it by ear.
Set a few planks of wood out to frame the perimeter and put the muck along the sides first off to secure the edges from bulging and leaking, then filll the centre from the back edge first to the front.
Shovel that gravel into the mixer and add some sharp sand to it as you see for. 2 to 3 grav to sand and a big scoop of cement will produce a nice strong concrete. Use a straight bit of timber to tamp the surface to the desired level. Keep the mix stiff to stop it all sagging. It will make it easier to level


Answered 25th May 2018

Is the concrete going to be the finished surface or are you laying slabs? You can add rubble, gravel, bricks etc to form a suitable base under the concrete to give it a solid base. I would hire a plate compactor to ensure the material is compacted. The concrete needs to be a min 100 thick and it may be cheaper and easier to get a small ready mixed load, dependent on access. If you need to mix by hand and want a nice finish add some sharp sand to a cement/ ballast mix in a 1/3/1 mix then you will need to spend time floating it up with a plastic float or some timber to get a nice finish . The previous answer explained about forming the perimeter with supported wood. Good luck


Answered 26th May 2018

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