How much sanding before fairing and paint
How much sanding before fairing and paint
How do you guys determine how much sanding to do on the hull before you begin fairing for paint? I am going to be painting both the bottom and topsides of the hull, but I'm not really sure how far to sand down the original finish. The bottom paint seems to be adhered very well, and the hull has no blisters whatsoever. The hull topsides is the original gelcoat that is a little crazed here and there, but is in good shape for th most part. I have no problem sanding the entire hull down to glass if that's what its going to take to get the best finish, but is this nessecary?
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Tim
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There's no hard and fast rule for how much you need to sand your hull, unfortunately. It's one of those things where you need to do as much as you need to, and no more or no less. (Real helpful, right?)
Seriously, though: if your topsides are original gelcoat with minimal problems, sanding is going to be a pretty straightforward affair. You're looking for a smooth, even surface, with no gloss remaining. Even for old gelcoat, you should first dewax/clean the surface before beginning your sanding, as waxes and mold release products can be surprisingly tenacious even if there is no external evidence of them. Begin with a commercial degreaser, and then use a solvent wash (something like Awl-Prep plus, a heavy-duty dewaxing solvent) to remove any such traces, whether you know they are there or not.
Once this is done, sand the gelcoat only as necessary to dull/smooth the surface and make it evenly abraded. If the surface is generally smooth and fair and in good condition, beginning with 120 might be sufficient; if it's in worse condition, begin with 80. Go to 80 grit only if you find that 120 isn't doing the job, or is ridiculously difficult. Gelcoat is soft and usually sands easily; be wary of using a tougher grit than you need, as the scratches can be tough to remove completely. I'd sand it as far as 220, and then begin your repairs and fairing as necessary. Be sure to sand thoroughly with each grit.
On the bottom, I wouldn't worry about too much sanding if the original paint is in good condition. A quick sanding to abrade the surface will more than suffice with traditional bottom paint.
Seriously, though: if your topsides are original gelcoat with minimal problems, sanding is going to be a pretty straightforward affair. You're looking for a smooth, even surface, with no gloss remaining. Even for old gelcoat, you should first dewax/clean the surface before beginning your sanding, as waxes and mold release products can be surprisingly tenacious even if there is no external evidence of them. Begin with a commercial degreaser, and then use a solvent wash (something like Awl-Prep plus, a heavy-duty dewaxing solvent) to remove any such traces, whether you know they are there or not.
Once this is done, sand the gelcoat only as necessary to dull/smooth the surface and make it evenly abraded. If the surface is generally smooth and fair and in good condition, beginning with 120 might be sufficient; if it's in worse condition, begin with 80. Go to 80 grit only if you find that 120 isn't doing the job, or is ridiculously difficult. Gelcoat is soft and usually sands easily; be wary of using a tougher grit than you need, as the scratches can be tough to remove completely. I'd sand it as far as 220, and then begin your repairs and fairing as necessary. Be sure to sand thoroughly with each grit.
On the bottom, I wouldn't worry about too much sanding if the original paint is in good condition. A quick sanding to abrade the surface will more than suffice with traditional bottom paint.
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