How To: Tell If It’s Oil-Based Paint

You’ve got an old house with layers of paint and you’re ready to apply a fresh coat of paint, but you don’t know what you’re up against. That top layer of paint is staring you straight in the face and making you worried. How can you tell if it’s oil-based paint? And why does that even matter?

It matters because if you plan to repaint, oil and water (latex) don’t play well together. You have to prepare your surfaces differently if you want your paint to stick for more than an afternoon.

As a restorer of historic windows all my projects are covered with multiple layers of all kinds of paint like antique linseed oil paint, late 19th century oil-based paints, and modern latex paints. For the best results you should remove all the old paint, but that can take a lot of work or cost a lot of money.

In the interest of saving you money there is an easy way to tell if it’s oil-based paint or latex paint that doesn’t require any special skills or materials. Once you know the type of paint you have you can prepare it properly.

Testing For Oil-based Paint

For this test you’ll need to grab a cotton ball or cotton rag with acetone and rub it on the surface you want to test. If the paint softens or comes off then it’s latex or acrylic paint. If it is unscathed then it’s oil-based paint.

If you don’t have acetone handy then rubbing alcohol will work as will most nail polish removers since they contain acetone.

It may be hard to tell the results if the paint is white and you’re using a white cotton ball though. In that case, if the paint is white then I use a black rag (really any color other than white will work) for the test.

If it’s latex paint then in order to repaint all you have to do is wipe the trim clean with TSP cleaner and you’ll be ready for a fresh coat of latex paint. If it’s oil-based read on.

What to Do If It’s Oil-based?

If it ends up you have oil-based paint it’s not the end of the road. There is an easy way forward, you just have an extra step before painting.

Liquid Deglosser

The first option is to use a liquid deglosser to give your new paint something to adhere to. Wipe the surface with the deglosser and let it dry. Once dry you can paint directly over top of it with latex paint and you should have resolved the adhesion issues common to oil-based paint. This method is quick and cheap but not the best in my mind because it doesn’t always produce perfect results.

Oil-Based Primer

The best option, in my experience, is to prime the surface with an oil-based primer. You may be thinking, “I thought oil was the problem.” When it comes to primers it’s a different story. Oil-based primer bonds well to almost anything AND provides an excellent base for any paint whether you are going back with oil-based paint or water-based latex and acrylic paints.

Oil-based primers have a strong odor and higher levels of VOCs so make sure you have excellent ventilation when you use an oil-based primer. They also require mineral spirits to clean up spills and clean your brushes so be prepared for the extra work during cleanup.

Now you know both how to tell if it’s oil-based paint and what to do if it is. If you want to know more about working with oil-based paints see my earlier post How To: Paint With Oil-Based Paint.