What mix of concrete should I use?

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Hi,

I need to make a cavity floor repair due to the relocation of some pipework and am just wondering what would be the best mix to use? I have never concreted before so nothing is obvious to me! :) I was wondering if I would need to do anything special as I need it to bond with existing concrete,

Please see the picture here https://1drv.ms/f/s!AjnJhtmhYMJlhpZmWfHQBA4kbB8DGA

Any advice would be greatly appreciated!
 
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I guess its screed?

1part cement to 3parts sharp sand

Im not sure what prep is needed, it looks like a floating screed so it needs connecting well to the original or it will tend to break up.

Is that insulation underneath?
 
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Thanks for replying!, Yes it is insulation, I have some new insulation to lay down first to line up to the existing, should I then put a bed of sharpsand down on top of the insulation first and then screed? I have heard of some formula you can paint on existing concrete to help the bond just need to find it! :)
 
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Thanks for replying!, Yes it is insulation, I have some new insulation to lay down first to line up to the existing, should I then put a bed of sharpsand down on top of the insulation first and then screed? I have heard of some formula you can paint on existing concrete to help the bond just need to find it! :)

Usually PVA is used for something like that.

I did wonder whether some holes should be drilled and some rebar resin'd in as you are effectively forming a day joint.
 
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Are you proposing to bury those push-fit pipe fittings in or under concrete ???
 
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no, they are just temporary until I plumb the new towel rail
 
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Thank you Notch, I will look into rebar :)

Im not sure if thsts the best dolution, but screed on top of insulation is not too bad if it is 1 complete slab, once cut, you have a few weaker bits of screed sitting on the insulation and day joints could work apart.

Im sure a builder on this forum will be along to advise a practical solution......
 
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I was wondering about strength.. should I have posted this in the building section?
 
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