I know there is a lot of advice about this, but as a beginner, I need advice on whether I should continue with Sanderson primer/undercoat (I think it's oil-based) straight onto the walls (they are fully dry). This stuff is very thick and cannot be diluted - seems wrong to use it on the plaster. I have painted a small patch only and don't know whether to continue. If not, what should I go over it with, to ensure the end result does not look patchy over the area where I used this primer. thanks.