Concrete step replacement

[robgraham]

The story is this - my workshop is a wooden shed possibly 50+ years old ( it was old when I got the property 30 years ago). I'm having to do the 50+ year make over !

I've now worked out that the guy laid a rough concrete base without a membrane, built the woodwork and then laid a 40mm concrete floor inside against the framing - yes I know it's astonishing it's remained standing this long. Anyway that's being sorted. The other thing I've worked out is that the entrance door was originally at one end but was moved to the side with the frame work cut away at that point and a bit of new concrete added to form a door cill. It also explains why the lintel is so low at that point such that every so often I scalp myself on it! - that also is going to addressed.

It's this 40mm deep x 75mm wide x 800m long step that has broken up completely and needs replacing. The base is rough concrete.

Do I just paint the base with neat PVA and add a dollop of PVA to the screed/concrete; how much is 'a dollop' and do I lay the step with the painted on PVA still wet?

Thanks

Rob

[Stuart Noble]

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.

[Andrew Gabriel]

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).

[robgraham]

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

Rob