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Morning all.
I'm in the throes of making a concrete perimeter footing for SWMBO's greenhouse.
6" thick walls, due to site slope it goes from 6" deep in one corner to 16" deep at the diagonally opposite corner.
I've placed rebar mesh on edge within the wall, and poured the concrete to a depth of 3" below the top face, the rebar is still proud of the concrete.
My question is do I need a bond between the final 3" of concrete and the existing stuff (will be 2 days old by then, been kept under covers the whole time).
I'm imagining an SBR/cement slurry painted on and allowed to dry wouldn't hurt, what say's the collective?
Thanks in advance,
Nick
If I’ve understood right, you’ve currently got a slab that’s 3” thick at one end and 13” t’other. You wish to raise it by a further 3”. Right?
In which case the final 3” is really a screed. It’s a bit thin for regular concrete. That means considering finer aggregate or indeed just sand. Definitely sbr slurry as primer. Possible add sbr to the whole screed mix.
Is green house a euphemism or is it commercially sized .... Cause that's some substantial foundations and blockwork your doing !
If you need to raise walls by only 3” and wall top is level use 1 course brick? need to cut mesh off with concrete,clean all loose bits off with wire brush and carry on with sbr etc either way can you then fix g’ house down into existing concrete rather than 3” layer
@trail_rat, the greenhouse is 12' x 8', it still cost considerably less than my last bike so no judgement here!
Hoping to get 10mm ballast for the top section, this situation has come about as a combo of bank holiday delivery restrictions, a broken trailer and my health not being all that, I realise the 2 part pour isn't ideal but I'm dealing with the possible here!
Hopefully the rebar, finer aggregate and SBR will suffice, the footings are recommended to be concrete not brick or block so the greenhouse gets fixed to one solid lump rather than (in time) individual bricks.
Thanks for the replies so far 🙂
If you have a pressure washer, you can blast off the surface laitance before it gets too hard, then apply the SBR to the concrete below. If no pressure washer, a wire brush.
When you concrete the next layer, keep the mesh 4cm below the surface. As concrete ages, it reacts with CO2 in the air and becomes less alkaline, which allows the reinforcing to rust. The expansion of the rust splits the concrete.