When painting over old paint, it is important to determine if it is oil-based or water-based so you can properly paint over it the first time. If you paint water-based paint over an oil-based paint, peeling and streaking might occur.
Below is an easy way to to tell which type of paint is already existing on a wall.
If purchasing new paint, the type of paint will be printed directly on the bucket or a salesperson will be able to let you know immediately. Oil-based paint usually has a very strong odour and requires white spirit to use on walls.
Visit your local hardware store and buy a small can of methylated spirits, also known as denatured alcohol. It should be in a metal can sealed with a safety lid.
Dip the rag into the spirits so a piece of the rag is saturated. It is helpful to use a rag that is an opposite tone of the paint you are checking, so if any paint comes off you will see it immediately.
Hold the rag against the wall you want to test for about 30 seconds.
Move the rag away from the wall. If the paint appears soft and begins coming off the wall, then it is water-based paint. If the paint does not move, it is oil-based.
Methylated spirits are highly flammable. Make sure to not store the bottle near an open flame.