The Loose Association of Wargamers

Largely because the site gets banned whenever people tell.

I've never felt a great need to prime coin bases unless they're especially new and shiny. PVA does 'bead' somewhat on them, but I tend to find that a thin membrane of PVA adheres to the whole base and gaps very rarely appear after it's been dipped in my usual basing sand (unless the coin is very new and shiny, as mentioned above).

In the case of 28mm figures, I also tend to stick them to the base first before painting and spray-varnishing, so the base ends up getting part-primed and then fully varnished before slapping on the PVA in any case, so that probably helps.