Concrete over concrete

[Ex-repairman]

Sorry guys but wasn't sure if this belongs in "Building" or here.

I want to concrete down between my garage and conservatory walls, a gap of about 3/4 metre. The DPC on the garage is too low so I appreciate that I will need to leave a gap, possibly filled with some form of gravel, to prevent damp problems in the wall. I have plenty of height below the conservatory DPC (> 150 mm) so assume I can concrete right up against it?

I remember the builder that did the base of the conservatory saying that there appears to be an old path below some loose laid slabs in this area, although he thought it was in a poor cosmetic state.

My intention is to clear the site back to the old concrete path and extend this old path out to the front edge of the conservatory, using compacted hardcore as required, and then 'float' some concrete over the top of the old and out to the new perimeter. Are there any special considerations for doing this? Is there a required thickness of new concrete to allow it to bond? Will it just crumble?

Many thanks for any advice.

 

[noseall]

so long as the new concrete is over 3" thick and made of 'good stuff' i cant see you having any problems.

...provided of course there is no sulphate contamination within.

seriously, a couple of buckets of water chucked around the area to be concreted will afford you a good connection and prevent any cement products drying out too quickly.

 

[Ex-repairman]

Thanks Noseall, although your 'sulphate' comment went over my head I'm afraid!!

What mix would you recommend? And have you ever used cement colour additives? Can you recommend a manufacturer/supplier?

Many thanks.

 

[Bylough]

Hi may I suggest also that you consider- if the path is longish- putting in expansion strips every so often.