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Solids, is the material that remains after the solvents evaporate and is the material that forms the film or coating. If you have more or higher solids in a gallon of lacquer you will have more film or coating left in an equal application. For instance, if you have a 25% solids lacquer and you spray out 4 wet mils of material you will end up with one dry mil of finish since 25% of 4 equals one. If you add reducer you will reduce the solids content so if you have a 25% solids lacquer and cut it 1:1 you now have a 12.5% lacquer since you diluted the solids by 50%. A higher solids lacquer will build faster since you are leaving more material per coat. Viscosity doesn’t necessarily correlate to solids content. Different types of nitrocellulose or other resins yield different viscosities as well as hardness. You can easily formulate a higher solids product with a lower viscosity than one with lower solids. Certain solvents will drop viscosity faster than others enabling you to lower the viscosity further with less solvent. Other solvents take more volume to make the same reduction in viscosity and reduce the solids more. This is dependent on the resin used in the formula and its solubility in different solvents.
As I mentioned earlier the resins affect the hardness of the lacquer as well and can be manipulated to accomplish different characteristics. This is one reason why you see different solvent blends and materials listed on different types of lacquers. Others could be dry times or flow out. A furniture grade lacquer used in a production environment may need different characteristics than an instrument lacquer where optimal flow out and rubbing characteristic are more important than faster dry times. Our Stringed Instrument Lacquer is made softer to provide the flexibility needed to hold up on a thin bodied instrument like an acoustic guitar. These thinner woods are more likely to flex or move than thicker woods and the lacquer needs to be able to flex with them. It is also common to build thicker finishes as well on these instruments and thicker films are more brittle than thinner films. Harder lacquers have limits to the maximum film build allowed to prevent them from cracking as these woods come and go. This is why you will often see a limit of 4 dry mils on most of our furniture grade finishes. These coatings are designed to be really hard to withstand the rigors of household furniture. If you use these lacquers on hollow body guitars and exceed 4 mils you can just about ensure that it will crack. On the other hand you don’t often see a vase placed on a guitar or need to stand it on end to get it through a doorway. They aren’t packed in cartons and stacked 10 high in a trailer for shipment with a high weight per square inch placed on them either so you can get away with a softer finish.
Michael,
The solids make up in our instrument lacquer is a proprietary blend of nitrocellulose, alkyd, gum resins and plasticizer. Every thing else in the formula evaporates away leaving these materials to form the film finish. In the case of a sealer or a flattened lacquer you would include the sanding aids and silica flattener and any other material that remains to form the film.
Most lacquers will bond very well to a properly prepared bare wood surface and can be used in a self sealing application. Stearated lacquer sanding sealers, which for years have been the predominate furniture sealer, are nothing more than nitrocellulose lacquer with the addition of stearates to aid sanding. While there can be other differences in formulation they’re basically the same. Therefore self sealing with a lacquer topcoat would give you an equal bond but would be more difficult to sand. The addition of vinyl resin to a nitrocellulose sealer does have some adhesion improvements and improved resistance to vapors. Most vinyl sealers are stearate free to prevent a reaction with catalyzed finishes. Shellac has very good adhesive properties, sands well and provides and excellent barrier to oils, contaminates and stains which can bleed upward. It imparts a nice amber color tone into the wood which can enhance its appearance if you are finishing a natural wood finish or using it as a pre-stain sealer. It is compatible to lacquer and will work well with it but it can be hard and more brittle in nature so I would limit its use to a seal coat and then proceed to your lacquer topcoats. If you are using heavy stains and glazes I would prefer lacquer as a sealer since the solvent blends in lacquers are better able to permeate these products ensuring a bond to the substrate below.
Thank you,
Phillip Pritchard
Mohawk Technical Service Representative
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