You have old stencil concrete or covercrete or just exposed aggregate and you want to give it a birthday. It is very important that the concrete is correctly prepared before anything new is installed over the top.

Often an acid wash is insufficient in correctly preparing the surface. If you have covercrete and its peeling away (delaminating) then the whole surface needs to be ground back to allow for anything new to correctly bond. If you just pain over the top it will peel off. One way you can grind the surface is using a wet grinder. This is a petrol powered grinder that requires the surface to be wet. Whilst it will create a bit of a mess (slurry) this is a fairly fast and effective way for grinding outside. If you have exposed aggregate then really this is the only effective method of grinding. Once you have ground the coating off in the case of covercrete or stencilcrete or you have ground the exposed aggregate flat with the cement, then the concrete is ready for you to either paint it or have a contractor reinstall covercrete or simply seal and leave it natural.