If unsure about moisture with in the pool substrate particularly with Marblesheen (Pebblecrete) and render a simple test will tell you if it’s too damp to paint. Get some heavy duty clear plastic sheet and cut into squares about 500mm. (you need 2 – 4 of them) Tape them securely around all edges to the pool surface and leave 16 hours, (over night). Check to see if any moisture droplets on underside next day. If so, it’s too wet to paint. Remove, let pool dry out for another few sunny, windy days and repeat until no moisture is present. Then you can paint. If you paint over a surface with moisture behind (underneath) you risk the Epotec bubbling up and coming off, as shown in the pictures here, under the clear plastic. (This is not the same as some dampness on the surface, which is acceptable) The right hand picture shows moisture droplets on underside of plastic sheet after overnight placement

A clear plastic sheet on bottom.

Moisture droplets on underside of sheet. Meaning too wet to paint. The Epotec has come away as was too wet within the substrate to paint.