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Old 03-28-2013
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Bottom Sanding

This is the first year I have worked on getting the bottom smooth and I sanded with 220 grit sandpaper with an orbital connected to a HEPA vac. I was thinking about doing a final sand with a higher grit sandpaper maybe around 400. How do you prep your bottom prior to launch? What grit do you end up sanding too?
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Old 03-28-2013
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Re: Bottom Sanding

mm,

I'm a little confused...

Are you prepping for bottom paint, or are you trying to polish a non-painted bottom?

If you are prepping for bottom paint, you are going in the wrong direction. If you use too fine of an abrasive, the paint will have a lot of difficulty adhering to the hull and it will ultimately come off in sheets.
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Old 03-28-2013
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Re: Bottom Sanding

Right.
If you are merely prepping to put new paint down on top of the old paint (now sanded) you don't need to go to extremes with fine sandpaper. You want to leave some "tooth" for the paint to adhere to, hence a final grit of around 150# or so is fine.
If, on the other hand you are sanding your bottom that has no paint on it and trying to make it smooth like a babies bottom you can really go crazy with the fine grits 220# -> 320# -> 440# -> 600# -> 1000#.
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Old 03-28-2013
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Re: Bottom Sanding

Hey,

Pettit paints recommendations for previously painted surface (this is for SR40 but most are the same):

Previously Painted Surfaces:
If the previous coating is in good condition, thoroughly sand with 80 grit paper then solvent clean with 120 Brushing Thinner to remove residue. Apply two finish coats of Ultima SR-40. If the previous coating is soft or in poor condition, remove to the bare surface by sanding or using a paint & varnish remover. Proceed with appropriate bare system as described below. Old tin copolymers must be removed before applying Ultima SR-40

http://pettitpaint.com/fileshare/pro...ds/1109206.pdf



I use 40-60 grit to remove old paint, then 80 grit to smooth it and give the right amount of 'tooth'. If I had a race boat I would use different paint and then wet sand, but that is too much work for me when I could be sailing.

Barry
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Old 03-28-2013
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Re: Bottom Sanding

you are reminding me of all those things I will be doing soon.. sanding is very low on my list of things I enjoy
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Old 03-28-2013
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Re: Bottom Sanding

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Originally Posted by mad_machine View Post
you are reminding me of all those things I will be doing soon.. sanding is very low on my list of things I enjoy
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Re: Bottom Sanding

I know.. Friend of my mom's years ago was refinishing her coffee table. She sanded it down and then appllied a nice varnish. Between the dust in her lungs from sanding and the varnish fumes.. she badly badly damaged her lungs.

This was 30 years ago.. not sure if she is still around or not.. but I know she was in pain with every breath for a very long time
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Re: Bottom Sanding

I am VERY surprised the yard allows you to dry sand even with a vac system!

I wet sand with 80 grit. I have an angling head like a Swiffer mop fitted to a broom handle. It holds a 1/4 sheet. It makes the job easier quicker and hence a lot less tiring.
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Old 03-29-2013
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Re: Bottom Sanding

Bottom paint is so thick that it's pointless to prep with fine grits - I don't go finer than 80 on an orbital. If you want a super slick bottom you use the fine grits on the paint, not the substrate.
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Old 03-30-2013
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Re: Bottom Sanding

I came home today blue!
Thursday, Friday and Saturday to scrape, sand and two coats of bottom paint.
Man! Are my shoulders and knees sore!

DeWalt 5" orbital set up on the 6 gal craftsman vac did the trick! No blue snot... I ended up using 80 grit; as the 50 grit that I got was a tad too aggressive. I razored the remains of the barnacles off.It was easier than sanding and boy! howdy...do those critters eat sand-paper! Only 6 discs for a 27'hull ! Two-thirds of a gallon of Pettit Sea-Kote (?) later and she's ready to go back in!
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