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What is Spar Varnish?

By Jodee Redmond
Updated May 23, 2024
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Spar varnish is a high-gloss product that is used for outdoor applications, including wooden furniture. It is also known as "marine varnish." This type of varnish is made to provide protection from changes in temperature, as well as the sun's ultraviolet rays.

Wood is a living product, and it responds to temperature changes by expanding during warm weather and contracting when the mercury in the thermometer dips. Varnishes made for outdoor use must have a certain degree of flexibility, or the finish will crack. A spar varnish is also made to be water-resistant, since exposure to moisture will cause wood to rot over time.

Light amber in color, this finish is made with tung oil and linseed oil, as well as phenolic resins. The better grades of spar varnish have a higher level of tung oil in the product. Some manufacturers produce a product that doesn't contain any linseed oil at all. Linseed oil does break down over time, and causes the finish to deteriorate.

Before using spar varnish, read the instructions on the container carefully. They will indicate how long the product will take to dry. Another important bit of information on the label is the recoating time. The user will need to give the varnish some time to cure in between coats, and it's better to apply several thin coats than one thick one.

Another tip that will be in the instructions is whether the product should be thinned with mineral spirits before use. Adding between 5-10 percent mineral spirits will help to make the spar varnish flow off the brush more smoothly. Pour some of the varnish into a separate container before adding the mineral spirits. Do not return the thinned varnish to the original container after use.

A good quality bristle brush should be used to apply this product. Look for tapered bristles when choosing one. Dip the brush into the container and press it against the side to remove any excess product before brushing it on. This product works best when applied to a small area at a time. Over brushing leads to bubbles on the surface where the spar varnish is being applied.

Before applying a second or a third coat of spar varnish, sand the surface thoroughly. It should be wiped off with a tack cloth to remove any dirt, dust or particles before adding more varnish. Always let the varnish dry thoroughly in between coats.

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Discussion Comments
By John57 — On Aug 31, 2011

I have some log benches that sit outside in the weather all the time. I try to keep them looking in good shape and apply some exterior spar varnish from time to time.

This does a good job, but I have found that it is best to apply this in very thin coats. If I apply it too thick, I will get little bubbles that surface and make the finish look and feel rough.

When I use a good, clean brush and make one pass with a thin layer it works a lot better. I wait until it is completely dry and apply another thin layer to give a smooth, glossy finish.

By LisaLou — On Aug 30, 2011

We always look forward to hot summer days and spending as much time out on the boat as possible. I am always sad when we take the boat out for the last day of the season.

After this, I know I need to get the boat ready to store for the winter and be ready to use again in a few long months.

This process always involves applying some marine spar varnish to the wooden parts of the boat. The water can take quite a toll on the boat, and you need a product that is going to take the abuse from the water well.

It takes some time because I like to apply more than one coat and do some sanding between coats so it continues to have a nice, glossy finish.

When I get the boat out for the first time the next season, I am always glad I spent the time to apply the varnish and keep the boat looking nice.

By golf07 — On Aug 29, 2011

Every fall I apply a couple coats of minwax spar varnish to some wooden chairs that sit out on my front porch.

Even though the porch is covered, the chairs still get weathered from some rain and the elements of being outside.

When the season is over and I am putting the chairs away for winter, I like to apply some spar varnish so they continue to look nice. I like a glossy finish and something that holds up well outside, so this type of product is a perfect solution.

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