Varnishes for Fiberglass: Best Tips on to Prolong Fiberglass Hull Life

Some boaters look at their fiberglass boat and are happy with coating it with a gel-coat every year or so to keep the hull protected. Others spend a lot of time on their boat and recognize that gel-coats may be great at first, but wear down over time. The best solution to maximize protection of your fiberglass boat is to paint and apply layers of varnish over the waterside hull.

When you’ve finished applying epoxy paint to your fiberglass boat – be it a yacht or a kayak – you must let the epoxy cure totally before you apply varnish. Most painters will let their boats sit from anywhere from two days to one week before they apply the first coat of varnish. Allowing the epoxy paint to fully cure – especially if it has antifouling properties – ensures there is a good seal between the paint and the boat substrate before you put more wet media against it (i.e. varnish).

Once you have a cured surface, very lightly sand the hull with 220 grit sandpaper. Ensure you use a sanding block to get an even sanding job, and save your sanding block for between coats of varnish as well. Then, wipe down the entire hull. Also spray water with a plant sprayer in the work area to ensure dust is removed from the air about a half hour to an hour before your first varnish application.

Use pure water to wipe down the surface of your boat before coating with varnish and dry with clean paper towels. Using anything else can risk surface contamination, which can cause your varnish to mar or dry unevenly. Ensure the temperature of the area is steady – between 70 degrees to 72 degrees – and the dew point is well below 80.

Varnishes for Fiberglass

Varnishes for Fiberglass

When you’re ready to apply your varnish, use three brush strokes: once with the grain of your fiberglass (horizontal), once against the grain (vertical) and then one last time again with the grain. This ensures maximum even coating of the varnish. Give your first coat of varnish on a fiberglass boat several days to dry before sanding. Once it’s dried, get your 220 grit-sanding block ready and go over it again.

In between coats of varnish, make sure you keep the rim of your paint can free and scum-free. Varnish is especially susceptible to contamination. If you find that your varnish has gotten dust or debris into it, you should start fresh with another can to ensure the best absolute finish on your boat. Why waste all that time applying bad varnish?

Repeat the sanding and varnishing process at least two to three times. More is always better and eventually, you will get a slick mirror-shine finish on your fiberglass boat. Of course you could have gotten this with a gel-coat, but nothing lasts as long or provides the same level of protection as a beautiful professional marine paint job.

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