Why does the polyurethane finish I put on projects turn yellow after a few months?
Simon Watts: It’s most likely the wood that is turning yellow rather than the finish. However, most clear finishes will deteriorate, to a greater or lesser degree, when exposed to direct sunlight.
Michael Dresdner: As a rule, neither oil nor water based polyurethanes turn yellow after a few months, so clearly something is amiss. The one exception is a moisture cured urethane finish that was taken off the market and recalled several years ago. It would turn bright yellow in sunlight. Considering the short time it was marketed, and how long it has been off the market, it is highly unlikely that you have any of this.
Some woods can become more yellow in just a few months of sun exposure — are you sure this is not what you are seeing?
