We are often asked whether certain guitar finishing products are compatible with others. With so many great finishing products available, it is tempting to try a new combination of filler, sealer, and finish. But caution is in order. Even if you carefully prepare a test piece, there is no guarantee that incompatibility between finishing products won’t generate unwelcome results weeks or even months into the future. That can lead to a very unhappy luthier.
The first thing we want to clear up is that we (Luthiers Mercantile) cannot judge the compatibility of products that we do not carry. Even products that are likely very similar in their composition, nitrocellulose lacquers, for example, may have differences between brands that could lead to problems down the line. It might seem like a fairly safe bet to apply one lacquer over another (or use one brand of sealer with another lacquer brand) but the threat of having to refinish a guitar, perhaps after it has already been delivered to a customer, should dissuade you from trying it!
The safest route is to stick with products within a single brand, but that is not always possible. Here are some guidelines to help you. If you have any doubts after reading, please feel free to call or email us. We are happy to help!
Shellac. Seems to be compatible with everything when used as a sealer, but be sure that the solvent (alcohol) is fully evaporated before applying any finish, especially a water-based one. This recommendation applies to dewaxed flake shellac, like the kind we carry. Avoid pre-mixed shellac products from the hardware or paint store. Royal-lac, which is a great product on its own, might also have issues if used as a sealer beneath other finish types.
Solvent-based pore fillers. We do not recommend you use with waterbased finishes
Water-based pore fillers. We do not recommend you use this with solvent-based finishes. One exception is the LMI Pore fillers we sell. They are compatible with any finish.
Epoxy filler/sealers. The ones we carry we know to be compatible with both solvent and water-based finishes.
Oil finishes and varnishes. These should be used alone. Do not combine in any way with other finish products.
Aquacoat This water-based filler is compatible with lacquer just be sure it has completely dried before finishing.
Waterbased finishes. Though combining nitrocellulose lacquer types might be okay in some circumstances, the differences between water-based finishes are far greater and so it best to assume they are incompatible.