can anyone help me with a concrete question ?

[Everett S]

I had to put a drain pipe under my sidewalk at home last weekend. I didn't mix enough concrete for the job and need to expand my culvert. Can I put a new layer of concrete on top of the first or will this cause cracking ?

[ozwinner]

Hi
I wouldnt be putting new concrete over old, unless it is a thick layer.
If it is a thin layer you will find it will crack, and lift off after a while.
There are poducts around which you paint onto the old concrete, and add to the new when wet that is supposed to bond both together, but I'm not sure that they work all that well.

Cheers, Allan

[journeyman Mick]

Everett,
you'll need 50mm min thickness, more if you'll be driving over it.

Mick

[glenn k]

PVA glue will help hold layers together. Usually bought as bondcrete but same stuff