gouache over Acrylic paint?

It can be done but it will be a fragile painting. As soon as acrylics dries it becomes a waterproof skin that will only stick to another layer of acrylics. flakes and cracks will almost be inevitable... but that may be a stylish effect.

'Priming' the painting with some clear acrylic medium will ensure a good binding but you need to work fast as it will only help as long as it's wet. Gouache can also be mixed in while the acrylic paint is still wet and become basically acrylics itself but once dry.... not really a good idea.

I asked this in a college design class a few years ago. My professor had experimented with the technique. Essentially, gouache over acrylics can work. However, you should not place acrylics over gouache.

It should be fine. Acrylic is plastic, so if it's dry the gouache should work on top of it. Just don't water it down too much, or it won't be opaque enough and it won't show up as well.

I'm not so sure that it will work out.