How far is too far with sanding

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Cruiser
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Location: Bowmanville, Ontario

How far is too far with sanding

Post by Cruiser »

I just finished sanding the outer hull with 80 grit ... I have the weave pattern showing in a few places, but I think it is epoxy laydown pattern. Problem is that I don't really know what the FG would look like if I really did get that far.

What I have is not a white colour, which is what I think the glass would look like if I was actually that far down. This is more like the off white of the sanded epoxy .... the pattern is the same colour as the sanded epoxy.

If it turns out that I am that close, I think I would just roll on a thin epoxy coat and then hand sand for the final finish with 120.

Any insight would be most appreciated.


Brian
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Jim Dodd
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Re: How far is too far with sanding

Post by Jim Dodd »

Hi Brian

Just finished sanding the outside of my hull.

When you start seeing weave, stop. If you see wood, that's to far. Time to patch.

What I do, is sand down just enough to remove the shiny spots, feather out the edges of my second layer, and the bias strips, two on each end.

When you varnish, the weave will disappear.

Don't worry if you just have small areas of weave showing.

I also used 80grit. Tried the same grit on an old paddle that I had glassed years ago. I went through two papers, and I'm still sanding ! Age really hardens that stuff.

Good luck !

Jim
Keep your paddle wet and your seat dry!
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John Michne
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Re: How far is too far with sanding

Post by John Michne »

When you are doing the fill coats, you will get to a point, usually after the third fill, where you see the weave is filled. But then you sand it, essentially converting the last coat to sanding dust which is now no longer on the boat. My rule of thumb is when I reach the assumed last fill coat, I scrape the runs off and sand lightly, then add another coat. Since the runs and bumps were previously scraped off, the final coat will be relatively smooth, thereby requiring less sanding and leaving more epoxy on the boat rather than on the floor.

If you see the weave after sanding, beware. You can varnish over it and it will become seemingly invisible. When viewed in sunlight, though, it readily shows.

John
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Jim Dodd
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Re: How far is too far with sanding

Post by Jim Dodd »

Good points John !

To avoid runs, I apply while the previous coat is still tacky. This Really eliminates runs, and no sanding !

Resins differ in the amount of coats needed. When I was using System Three's Clear Coat, I would apply as many as 6 coats to get that extra fill coat, as you say gets sanded off. I really liked the Clear coat.
On my latest, I used RAKA, and the 350 non blushing hardener with great results. Three coats pretty much did it, but the fourth was my insurance policy.

Jim
Keep your paddle wet and your seat dry!
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Cruiser
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Re: How far is too far with sanding

Post by Cruiser »

Since this is my first time FGing and therefore also the first time sanding, I am wondering if there is any difference in the colour/appearance of the weave pattern that might tell me that I am at the glass or just the epoxy pattern.

I don't think I have over sanded, simply because I am using a good quality paper, but I have only used 3 pieces (5" ROS) for the whole outer hull to this point. I sort of thought the actual FG would likely show as a white pattern as opposed to the offwhite of the epoxy pattern, I figured it would be better to ask than to experiment by continuing. This is not a stage I want to messup.

Just as an aside, for the sanding all I was trying to accomplish was to smooth out the epoxy and make sure I had most of the gloss removed, leaving smaller bits for the 120 second sand. The boat is a Freedom Solo 16 version, and I have only sanded to where the hard chine starts, simply because the chine to the sheer should be a lot easier to handle, once the boat is removed from the molds and placed upright.

Putting a thin epoxy finish coat is not the end of the world (it is a pita with the curing time though), but I want to be sure it is required.

Thanks for the continued support

Brian
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