You cannot use any acrylic polymer, such as tar gel, over cwm or cwm/oil surfaces, unfortunately. As nice as it would be, there is inadequate
adhesion between the cold wax medium and acrylic polymer. However, you can do the opposite - you can work with acrylic/polymer mediums such as tar gel (and in my case I add the extra step of coating with acrylic clear gesso) and then proceed with cold wax/oils.