Thinning Varnish

Varnish can be thinned by adding a solvent to the varnish to reduce its viscosity and improve the brushing ability and flow quality. Be sure to use the solvent specified by the manufacturer. Certain solvents will be better for warm or colder conditions; others are used specifically for brushing or spray applications. Only use the minimum amount of thinner possible to achieve the highest gloss and promote the fastest dry times.

The first coat of varnish is typically a “sealer” coat, which is varnish that has been thinned substantially, so it sinks into the wood grain. Straight varnish is too thick to do that effectively. The amount of thinner recommended for the sealer coat depends on the varnish, so read directions carefully.

For example, a traditional varnish, such as TotalBoat Gleam, is typically thinned up to 50% for the first coat. In contrast, TotalBoat Lust, with its 1-hour overcoating capabilities is thinned 100% for the first coat only, to achieve maximum penetration into the wood grain.

The sealer coat is followed by a succession of “build” coats, before the final coats are applied. The build coats are thinned as needed to make the varnish lie down easily and level out smoothly. More thinning may be necessary in warmer, more humid conditions. Take care not to add too much thinner, as this will affect cure times and gloss levels. The final coats of varnish are usually applied at full strength, with no thinner added.

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