Can You Spray Polyurethane on Oil Paint?

Considerations

• Oil-based polyurethane is suitable for spraying on oil paint, as they have the same base. Oil-base polyurethane generally dries to a tougher and glossier finish than a water-based polyurethane, and with fewer coats.

  There are some drawbacks. Oil-based poly is more susceptible to dulling and yellowing over time than its water-based counterpart. It will have more fumes and VOCs (volatile organic compounds), which may be a consideration if you have limited ventilation and cannot move the object you are coating.

  Moreover, there are some areas of the U. S. where oil-based polyurethane is not available, due to environmental regulations. If you encounter difficulty spraying oil-based polyurethane, it can be helpful to thin it slightly to improve flow; check with the instructions on the product to see the best solvent to use.

  Water-based polyurethane offers some advantages, but its adhesion to oil paint in all cases can't be guaranteed. The water-based polyurethanes are unrestricted in their availability, but require more work to apply to get an equivalent finish to the oil-based version.

  Water-based polys usually have lower VOC rates. They also clean up with soap and water, another advantage. There are some oil-modified, water-based products that will work over oil stains, but in any case, before you apply the water-based product to oil paint, check with the individual manufacturer to get recommendations on how to best use the product.

  You may need to sand the surfaces first, if that is possible without ruining the look, to provide better adhesion, and some manufacturers may recommend a barrier coat.