We have a footpath outside our sliding doors. We want to lay a patio. Is it possible to pave over the footpath and continuing paving onto the “grass” area to make the patio larger? Is it likely the slabs on the “grass” area would move over time causing cracking between the slabs set on the “grass” and the footpath?
But you rightly anticipate a problem on the extended area. You need to have a very solid base of hardcore stone, well compacted with a whacker, to make sure it does not sink relative to the concrete base.
In general, the best solution is to simply break out the concrete path and remove off-site. Then lay a soild 15cm foundation under the area to be paved. This approach gives you complete control over setting the new level.
It is not as big a task as it seems, or all that costly, to remove a concrete path.