This summer I will be painting the old home I just bought. I would like to match the type of exterior paint. How do I tell if the paint is oil based or latex?
Wet a rag with denatured alcohol and rub the paint surface. If paint comes off in the rag or the paints gets tacky, it is latex paint. If the surface remains untouched, it is oil based paint.
Most professionals do recommend matching the type of paint for good bonding and to match the hardness and flexibility characteristics. Often latex is applied over oil because it is more flexible and can breath if there are minor moisture problems.
Oil paint should not be applied over latex because it dries to a harder, less flexible, less porous, surface and to may peel and crack.