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27a. Varnishing - the tools and technique

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This is what I use on my kayaks. The varnish here is Z*Spar Flagship 2015. I use Z*Spar T-10 varnish thinner or Epifanes 333 brushing liquid for thinning and better flow-out.

The other indispensable tools are tack cloth, paint sieve to strain the varnish from the can and disposable foam brushes. Every coat will take one. It is possible to clean them with lacquer thinner but it is more pain (not to mention the explosive potential) than it is worth.

Actually, having said that, a used foam brush cleaned with lacquer thinner becomes a better tool on the next round of varnishing because all leftover dust is permanently stuck to it with the dry varnish residue AND the foam is stiffer and will not expand and soften like a 'fresh' brush when it comes in contact with the varnish solvents. This just means you will have more control over the working foam tip. I save the reused brushes for the final coats.

This is another premium quality varnish I am trying right now. It is paler in color than the z*spar.
This varnish seems to produce a slightly better gloss and is also more abrasion resistant (it is certainly harder to wet sand than z*spar).

For all its good qualities, it seems to dry about 2 to 3 times longer. While I customarily, sand and do one coat of z*spar per day, I find it impossible to do with the Goldspar. It just clogs up the paper.

"The Technique"

  • each half hull is done one at a time with the varnish seam at the keel
  • varnish is applied from the keel down to the sheer in a 2 ft swath at a time
  • I am going backward from the varnished area smoothing and feathering the 2ft section from the dry area into the finished coat. (Do parallel overlapping strokes to catch all drips and dry spots)
  • Avoid starting the brush stroke in the finished coat.
  • The surface can be wet sanded (320) at the same time the next day. (Assuming a dry shop)

It is not unusual to get a varnish sag or drip in every coat you put on (only practice and knowledge of varnish behavior will improve it).
The quickly drying varnish leaves only a short window of opportunity to go back and touch things up. If you don't catch these sags within 45 seconds or so, don't even attempt to go back and fix it. The fresh varnish will refuse to feather and blend seamlessly into the 'older' coat and more sags are sure to follow. Instead, wait until the next day and before you start to wet-sand for the next coat, highlight the high spots of the sags with a magic marker so that you can see them when you sand. Unmarked drips are completely invisible under a sheet of water. When the magic marker disappears, you know that the drip has been safely sanded out (spend some more time on the spot just to make sure).

I don't like to use power tools for sanding between the coats because even the fine grits (320-400) will sand through the thin skin. The best tool for large areas is a hand held 'plaster sander'. It works like a fairing board that continues to improve the quality of the surface by knocking down the high spots and allowing the dips and scratches to be filled.

With that said, don't rely on varnish as a filler. Five or six lightly sanded coats will hide all sanding scratches but not ripples from poorly sanded wood.
Use your hands only to sand the sharp contours such as the bow/stern tips. Remember that the varnish layers are vital in protecting the epoxy from UV light and not just for a glossy look.
The picture illustrates sanding with 400 grit before the final fifth coat.
After wet sanding the surface between the coats, the sanding residue (white powdery stuff )on the surface must somehow be removed. Using plenty of water and a rubber squeegee minimizes the usage of cloth and paper towels ( read DUST& LINT).
This tool is also good to check on the progress of drip and sag removal. Remember that ALL imperfections are completely invisible under a layer of water.

When dry, lightly swipe the surface with a clean tack cloth.

Don't sweat the imperfections, drips, shiny spots and dust on the first coats of varnish. Sanding will remove those and by the last coat you will be looking at gleaming KAYAK itching to get on the water!

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Last page update: 29 October 2013