Concrete step replacement

I make up a 4 water: 1 pva mix. Anything stronger than that can end up being counter productive. I don't think it matters whether you allow it to dry or not. The aim is to seal the substrate without forming a film over it. The flag and brick system described here might be simpler than modifying the existing step.

Neat PVA isn't either waterproof or water resistant when set, so long term I don't think it will help used in that way any more than if you didn't use it in the first place.

PVA does have quite different and special properties in cement though, and you can use it as part of a cement slurry to bond the concrete together. For this, I would suggest mixing up a slurry of cement/PVA/water in a 2:1:1 ratio. Paint this on and as you say, pour the concrete step on it whilst it is still tacky. In the case of a concrete to concrete bond, the PVA in the slurry is probably not strictly necessary, but if your old concrete has anything about it which might prevent a new cement bond forming with it properly, the cement/PVA slurry should still bond. If the step is going to be subject to excessive moisture (e.g. part submerged in a puddle when it rains), then use EVA rather than PVA (it's usually sold as Waterproof or Exterior PVA, but again, this is only when in cement, not neat, and it's only a bit more waterproof than PVA).

Many thanks, Andrew - that clears the slurry from my ..... well you know what I'm getting at.

Rob