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Sanding coaming

Submitted by aaronpotter on Sat, 05/04/2019 - 17:14

I’m getting close to finishing my Guillemot build after several years of work.  I did a final sanding on the boat before varnishing and decided that I would not be satisfied with the coaming lip.  I didn’t put a large enough radius on the fillet between the coaming lip and the riser so the outer layer of fiberglass pulled away from radius.  I sanded through the glass in several areas and dust got underneath leaving large white areas.  So I sanded more until the loose glass was removed.  I then mixed up some epoxy and cedar dust and put a larger fillet.  Today I sanded and sanded the radius smooth but found small white dots throughout the fillet. See pic below (the pic is upside down, vertical stripes are the rise, horizontal stripes are underside of coaming lip)

I’m not sure if these dots are due to air bubbles in the epoxy or have I not sanded far enough to totally level the surface?   Any suggestions?   I am really tired of hand sanding this tight area!

 

thanks,  Aaron

Coaming

Looks like sanding dust to me, try wetting with alcohol, if they disappear they are dust, so a little more sanding to completely smooth the surface is what is needed.

However nobody apart from you will ever see this area, so I would probably just leave it!

Justin

JohnAbercrombie

Sun, 05/05/2019 - 12:10

I agree with Justin. I wouldn't spend a lot more time sanding that area. 

If you have shop air, you could blow out the area (wear eye protection and open the window..).

Wetting with alcohol (as Justin suggested) is also a good idea. If you can get the dust mostly out of the pinholes, then painting on a thin coat of clear epoxy and warming it with a hair dryer to get the air bubbles to 'pop' can help. Or just let the varnish do the job, later.

mick allen

Mon, 05/06/2019 - 01:02

I developed a bad habit of stippling the resin into the glass by pounding a brush end vertically to wet out when I built a whole raft of polyester boats.  The habit stayed and in one of my later boats where there are lots of level inconsistencies I entrained a couple of trillion microscopic bubbles that then turned your nice white artifacts when I was trying to sand out those required level changes. Thousands literally from tiny to miniscule to microscopic.

So I tried everything: epoxy wetting, water hosing,  air, dental water high pressure 'toothpics' [I thought that would work for sure!], extremely thin SS wired brushes, swearing . . . the technique that ended up working like a champ was attaching a tiny medical syringe needle to a tube connected to a  low pressure source and individually blowing out each partially sanded thru bubble. In other words, the air was specifically directed into each bubble. White instantly gone.

It truly was magic - compared to the horrendous mess I originally had - every single hole was blown out. So there is hope, just try a bunch of different things. But don't resin over them before blowing out/removing or the problem is encased.

John VanBuren

Mon, 05/06/2019 - 08:11

Here is a possible solution.

A Nice coat of high gloss black paint in that small area would be a decent looking and easy solution. To get the visual impact you could mock up the area with black electrical tape to see how it would look.

John VB