Fairing the hull for topside paint

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lsheaf
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Fairing the hull for topside paint

Post by lsheaf »

Hey guys,

So I have quite a few chipped paint marks that had to be sanded out. Those spots will need to be filled and faired. I also had to sand 4-6 inches off above the waterline where there was severe bubbling and some signs of osmosis. Some areas were sanded down to bare fiberglass.

What techniques should be used for filling small sanded out chips as well as larger areas that need to be faired to follow the contour of the hull?

Many people suggest using a long board while others claim it is a waste of time and I only need an orbital sander.

Also some people have recommended not using west system 407 filler and to use awlfair because it works better? When I asked why, I did not get a clear answer.

So I’m not sure what if I need the long board.
lsheaf
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Posts: 66
Joined: Tue Sep 10, 2019 8:41 pm
Boat Name: Stardust
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Re: Fairing the hull for topside paint

Post by lsheaf »

Here are some pictures of the hull
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9AC302EE-4F23-4BB9-B20D-78FBAC93247E.jpeg
4F933D5B-F222-4E70-8F3D-A96CAC51B28F.jpeg
4E8FFE9C-B5EA-44F4-8235-8BA79131AAC2.jpeg
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atomvoyager
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Re: Fairing the hull for topside paint

Post by atomvoyager »

People tend to recommend what they're familiar with, myself included, so there's that bias to consider. The next thing is, for various reasons, don't expect a consensus of opinion on anything. Having said that, it looks like you can fill low spots deeper than 1/8" or so and any cracks that you V'd out with a dremel with a colloidal silica thickened epoxy like West System with 406 additive. That's tough to sand so don't use it for final fairing. After feathering the surface and sanding any 406, apply 407 fairing compound or equivalent (all the popular ones will work) to any remaining low spots or roughness remaining in the surface and sand it fair with the 5" random orbital sander. If you're not skilled with the orbital then you can experiment using a long board but it's slow and laborious and shouldn't be required in this case. Larger areas of low spots do need a long board in order to span the low spot and not undercut it causing waves and ripples in the finish. Also, get the area smooth to eye and hand before priming and don't expect the primer to hide any roughness.
lsheaf
Rough Carpentry Apprentice
Posts: 66
Joined: Tue Sep 10, 2019 8:41 pm
Boat Name: Stardust
Boat Type: Allied Seawind 30

Re: Fairing the hull for topside paint

Post by lsheaf »

I did end up doing some experimenting with a long board which, gave excellent results, but after my final 220 grit sanding with an orbital I realized the long board was quite unnecessary for most of the work. So I’m now done with fairing and ready for primer.
I also did some experimenting with West systems 410 microlight filler (not near the water line). It worked well for fairing underneath the hull deck joint (where I fiberglassed) but not where there was any 407 in close proximity. Some areas with 410 filler sanded faster than areas with the 407 filler, requiring another round of filling and fairing.
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