Hull painting

[Shrubser]

Eh so...... I've been sanding down my hull using a rotary sander and have made a few (a lot) of little half moons as a result. Any ideas about how to get rid of them apart from lots of manual sanding?

[scars_scrapes]

yeah, no. I always long board in an "x" pattern to start with the most aggressive paper needed, and work my way finer to get scratches out. I normally have a filler in the deepest scrathes. when I get a few away from the final sand I start sanding in the fore and aft direction, water flow direction along the hull.
your paint will fill some fine scratches but not much

[49208]

Originally Posted by Shrubser

Eh so...... I've been sanding down my hull using a rotary sander and have made a few (a lot) of little half moons as a result. Any ideas about how to get rid of them apart from lots of manual sanding?

Are the half moons deep enough that they catch your fingernail ?

Were you keeping the sander flat on the surface and what grit paper have you been using ?

Is this prep for painting or to bring the gloss back in the gelcoat ?

[Shrubser]

Originally Posted by 49208

Are the half moons deep enough that they catch your fingernail ?

Were you keeping the sander flat on the surface and what grit paper have you been using ?

Is this prep for painting or to bring the gloss back in the gelcoat ?

1. Yes they are.
2. Trying my hardest but obviously not hard enough. I was using about a 120 grit.
3. Prep for painting.

[Eric Schwing]

120 grit is WAY WAY too coarse.
What you need to do now is re-sand using progressively finer paper. The rule of thumb is that you can only double the grit number each time, so if you used 120, you can go no higher than 240, followed by nothing finer than 480, etc. You'll need to go to at least 600, sanded wet.

[49208]

I'm guessing you were using a heavy duty sander like this



Since you are painting, you can either fill the defects now and then do one more sanding (switch sanders) or switch sanders and keep sanding until you have removed the defects and have a fair/smooth bottom

This type of power sander would be better for you:


or go to hand sanding with something like this:


I don't think 120 grit is too rough for the intial sanding, on the right sander, especially now that you have defects to deal with - Depending on your paint system, you may only need to go to 220 grit anyway.

[Shrubser]

You would be correct in your assumption about what I used. Perhaps a bit heavy handed.

I guess what I was hoping to find out is - is it ok to keep sanding to remove the dents or do they need filled. They aren't that deep so I'm gonna have a go at using the traditional hand sanding using a finer paper and a long board. There's no easy way eh! Lesson learned though. Next time I'll ask here first before charging in.

Thanks for your continued help chaps, it's invaluable

[lumpy]

This article might help
http://www.woodbin.com/misc/palm_san...tal_sander.htm
Also don't put much downward pressure on the sander let the sandpaper do the work and change paper frequently once it looses its edge.

Another idea is to wear an inexpensive cotton glove as that will absorb some of the vibration that is transfered to your hand.

[49208]

Originally Posted by Shrubser

You would be correct in your assumption about what I used. Perhaps a bit heavy handed.

I guess what I was hoping to find out is - is it ok to keep sanding to remove the dents or do they need filled. They aren't that deep so I'm gonna have a go at using the traditional hand sanding using a finer paper and a long board. There's no easy way eh! Lesson learned though. Next time I'll ask here first before charging in.

Thanks for your continued help chaps, it's invaluable

If it were me, I would fill the defects as opposed to sanding them out. The chances of keeping the hull lines somewhat fair are better that way. I think it would be faster as well.

[Shrubser]

Ok, so fill them with what?

[49208]

You can get pre-mixed fillers such as


at most marine stores or online.

I would avoid going the super cheap route and using anything that uses talcum powder as the filler (The cheap Bondo uses talc)

You can also mix up your own by buying the components (Epoxy, vinylester or polyester resin and mix in either microballons or easily sanded fillers such as West 410 microlight http://westsystem.com/ss/fillers/

[scars_scrapes]

guys a few things, random orbital sanders are not the answer when you want to great bottom, especially one with curves like a laser, too hard to control and "feel". hand sand the boat is not that big so you can feel what you are doing.

also don't press down hard, the paper should do the work and yes you will need to change out often, especially as the grit gets finer. you can get a nice paint job in the 4-600 grit arena and if you have a talented painter even a little corser.

[Kratos]

Originally Posted by Shrubser

You would be correct in your assumption about what I used. Perhaps a bit heavy handed.

You...tried to "sand" your hull with a mini-grinder?

[Shrubser]

Eh yeah, but it did have a sander attachment, not a grinder