How can I tell if my existing paint is oil-based?Updated 4 months ago

To test what kind of paint you have, get a small amount of methylated spirits (Vodka or Gin will also work) on a rag that is a noticeably different colour to the colour that is currently on the surface. Give it a small rub, if the colour comes onto the rag, you've got a water based paint and if it doesn't do anything beyond cleaning it a bit, it's oil based. If you have water based paint, all you need to do is give it a light sand and clean it up before painting. If it's oil based, you need to give it a light sand and use a coat of Tint Prep Plus before painting, otherwise the paint won't stick properly and you'll find it'll all peel off if you nudge it.