Render Question - Sand finish to Acrylic

Hi All

I need some advice. The builder has made a fairly large mistake and I want it fixed properly. We asked for an acrylic render finish and they have completed the render in sand finish. They are going to apply the acrylic but I want to make sure it is done properly. At this point they have applied the coat of sand finish render, sealed it and then applied a coat of paint.

What would you expect them to do to prepare the current render to apply the acrylic render? Will they need to rough up the current surface and will the paint affect the acrylics ability to bond to the wall? Do they need to strip it back to brick and start again?

Any thoughts would be appreciated.

cheers