old-to-new concrete bonding ?

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Hello. I wonder if anyone has any advice or experience of bonding old concrete with new. I want to build a low wall on a sound exisiting concrete base/foundation, this is because; 1. digging up the concrete is a major headache, 2. the base is at least 3-400mm deep and 100mm wider than the wall on both sides so big enough, and 3. I'm afraid I'm looking to save some money and work. The wall is about 800mm tall (3ft ish) so not a big deal in weight terms.

My issue is how to bond the old existing concrete with a new levelling surface of concrete from which I will begin to build the first course? How about PVA painted on the old concrete and a PVA additive in the mix to bind them together, or is this a load of blx?

Any help gratefully received. Thanks.
 
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Old should be very clean. Then slap on some neat cement slurry. Let it dry off. Then pour on new concrete. That's what the concensus seems to be. Can't see what PVA would do for you.
 
cement slurry. pva is indeed a load of old *******s unless you are making something on blue peter
 
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Thanks for the help, appreciated.

Btw, cb9002, can you expand on what you meant by acid etching the old concrete, is this a formulation I can get from a normal builders merchant or is it a specialist thing?

I get the advice about a cement slurry, but I thought I'd just check above first before I go ahead.

Ta.
 
The new concrete is intended to create a level surface/foundation for the wall, so at it's thinnest it will be 100mm (4") and at it's thickest 200mm over a distance of 9 meters (600mm wide). This is what needs to bond with the old concrete.

Any advice on a mix for this application would be great if you think it requires something out of the ordinary.

Thanks
 
no it doesnt need to be acid etched at that thickness. 1:6 is fine
 

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