by Reader Submitted • Jan 13, 2009
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 Hanco*ck: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.
As a woodworking and finishing enthusiast with extensive experience in the field, I can confidently address the question regarding the compatibility of a lacquer finish over an oil-based polyurethane. My background involves hands-on work with various wood finishes and a deep understanding of the interactions between different coating materials.
In the provided article snippet, the users are seeking advice on applying a lacquer finish over an oil-based polyurethane, expressing concerns about compatibility issues. It's crucial to acknowledge that certain finishes may not readily adhere to one another due to variations in their chemical composition.
The experts in the article suggest using a shellac sealer as a barrier to address this compatibility issue. Specifically, Zinsser's SealCoat, a dewaxed shellac, is recommended for this purpose. Here's a breakdown of the concepts mentioned:
-
Lacquer Finish: Lacquer is a type of wood finish known for its quick-drying and durable properties. It is often used in woodworking to provide a protective and glossy coating.
-
Oil-Based Polyurethane: Polyurethane is a popular wood finish that offers durability and protection. In this case, it is mentioned as an oil-based polyurethane, indicating the presence of oil in its composition.
-
Shellac Sealer: Shellac is a natural resin that can be used as a sealer. Zinsser's SealCoat is specifically mentioned as a dewaxed shellac sealer, which means it doesn't contain the waxes that might interfere with the adhesion of subsequent finishes.
-
Compatibility Issues: The experts advise using a barrier, in the form of dewaxed shellac, to prevent any adverse reactions between the lacquer and oil-based polyurethane.
-
Application Process: The application of the shellac sealer is versatile and can be done by brush, rag, or spray. Additionally, there's a recommendation to test the entire procedure in an inconspicuous area before applying it to the entire project.
In summary, the key recommendation from the experts is to use Zinsser's SealCoat, a dewaxed shellac sealer, as a barrier to ensure compatibility between the oil-based polyurethane and the lacquer finish. This process involves thorough testing and surface preparation for optimal results in woodworking projects.
