The simple answer is no. You cannot render over paint.
We understand that not everyone has a large budget and people would be looking to save money where they can but rendering over paint is not one of them.
We get a lot of calls where people assume that we can render over paint and expect to do so with no issues. However, this is not the case.
The problem with rendering over paint is that there will be a weak interface between the paint and render. Any movement or impact on the rendered wall will cause the render to fall away due to a weak bond.
Also, organic growth will affect rendering over paint. Although it may have been brushed off, it can remain in the pours of the substrate. When this happens, delamination can occur. Delamination is the separation of layers which also means a weak bond between render and substrate. Again, any impact or movement to the building will cause the render to fall away.
The best way in order to avoid these weak interfaces and bonds is to remove the paint before rendering. In the short term, it may cost you more but in the long term, you save money. This is because if the rendering falls away before the 10-25 years that the render is meant to last then you will be paying to have the rendering re-done before you were meant to.
You would avoid any unnecessary costs if you remove the paint beforehand and the problem wouldn’t occur in the future. It is also good to note that no rendering company will offer any guarantees, if you decide to render over paint. However, if you do decide to render over paint, then please ensure that a lightweight render system is used. This will have a much better chance at lasting compared to a heavier render system.