Q: Is it advisable to pour a three- or four-inch patio on top of an existing one or is it necessary to remove it first? Pouring on top of the existing patio would not only be
cheaper, but it would also provide a raised border around the flower beds. Also, no doors or gates would be affected by the additional height of the patio.
A: Yes, it would be fine to pour three to four inches, or even a thinner layer, of new concrete over an existing patio as long as you have room under the weep screed, doors and gates.
You just need to apply epoxy over the top of the original patio to create a membrane between the two layers.
Also, the new concrete should be made with a higher sack mix and some fiber additive.
Ray Nelson, Nelson Concrete Works, Sacramento, CA