Primer is not waterproof. No paint is waterproof. All paint has an element of pourosity to it. If left enough then the surface of the primer will break down quicker as it’s not got a reflective coating.

Does paint primer waterproof?

A thin layer of paint may still be permeable to water. Water can permeate into the wood and cause warping, mildew, or dry rot. Primer improves the waterproofing of the finish.

How long after priming can I waterproof?

Priming of cementitious substrates is required if the substrate is damp, using Wet-seal Top-coat 300 Two-part Water based epoxy and allowed to dry for a minimum of 24 hours. Wet-seal Fibre-coat is tile ready in 48 hours (depending on temperature and relative humidity).