Finishing With Polyurethane

Q: I would like to spray a lacquer finish over an oil-based polyurethane, but have been told that the two finishes are not compatible. Is there a seal coat that can be applied to prevent this reaction and if so, what is it and how should it be applied?

Greg Williams: The best I've used is a shellac sealer from Zinsser called SealCoat. It can be applied by brush, rag or spray. Test the whole procedure in an out-of-the-way place before proceeding.

Kevin Hancock: Why do you want to do this? Polyurethane is a more durable coating. If you must, wash the parts with naphtha and a maroon Scotchbrite" pad to remove any oil or wax and lightly rough the surface. Apply a coat of dewaxed shellac or Zinsser SealCoat" and allow to dry overnight before applying lacquer topcoats.

Richard Jones: Use a dewaxed shellac as a barrier, and then spray your lacquer.

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