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Old 04-03-2005, 08:46 PM
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Default Power sanding gelcoat.

I am going to try one more time to restore my red gelcoat before I give up and paint it.

What is the easiest way to sand the gelcoat that will do it the fastest? Can I use some kind of a power sander even though I have to keep the paper wet? I suppose I could go buy an air sander but is this the best way to do it?

What grit should I start with and how will I know when I should switch to a finer grit?

I would appreciate anyone with any experience to give me some pointers as I'm going to start the sanding tomorrow.

Russ
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Old 04-03-2005, 11:15 PM
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Default RE: Power sanding gelcoat.

Have you tried this: http://www.aqua-buff.com/



I've used it on two boats (white gelcoat) and it brought the gelcoat back to showroom finish.
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Old 04-04-2005, 07:03 AM
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Default RE: Power sanding gelcoat.

Are you trying to remove oxidized gel coat? If so, on how large an area? This would be my decision maker. If I was trying to refinish a 4 sq foot area. i would do it by hand. If it's the whole hull, an air sander is the only way. I have a Craftsman 6in random orbital air sander that I used during the painting of my motorcycle and 3 repaird hatch lids on my boat. I have never looked for wet/dry discs for it. I suppose they make them?

Are you sure you need to sand it. What about going to an abrasive polish and an electric buffer? Check here for 3M polishing compounds.

http://products3.3m.com/catalog/us/e...er/output_html

Depending on how much gel coat you have to remove. These shold do the trick. Just start with something abrasive and move your way up to the finishing compounds. Their automotive stuff has worked great for me on the motorcycle paint jobs I have done.
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Old 04-04-2005, 07:55 AM
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Default RE: Power sanding gelcoat.

Being a chemist it is hard for me to agree with a physicist but I think kev is right. Before you start sanding, exhaust all the rubbing/polishing compound options. 3M Super Duty rubbing compound is worth a try. It is an aggressive compound that leaves a decent finish when used with a mechanical polisher.

Sanding should be your last option. Once you open that can of worms there is no turning back until the job is done and it is a hell of alot of work. Running a buffer is alot easier. Completely redid my boat bottom last season so I am speaking from experience. You can see the results here: http://thehulltruth.com/forums/thread-view.asp?tid=25754&start=1&posts=40. Burried in that link is a step by step that I wrote up that might help you out.


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Old 04-04-2005, 08:32 AM
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Default RE: Power sanding gelcoat.

Chemguy...That is a beautiful boat. I really like the simpleness of the way it looks. I'm even more impressed now that I have gone back and looked at the work involved. It should give all of us a little incentive to keep 'em looking good.
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Old 04-04-2005, 09:19 AM
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Default RE: Power sanding gelcoat.

Thanks for the responses but I think I've exhausted every chemical solution for the gelcoat. I have spent hours upon hours with at least 8 different rubbing compounds and color restorers buffing with my Makita power buffer. I've tried using 3 different buffing heads in combination with different chemicals.

I just looked in my cabinet and I still have these compounds that I have tried last year alone:

-3M Marine super duty rubbing compound.
-Mequires #49 heavy oxidation remover.

I tried a product my mechanic told me about made by Mary Kate products called Trewax rubbing compound. He swore it would do the job but after 3 cans the gelcoat only looked a little better. The gelcoat surface is smooth to the touch even where the heaviest oxidation is. I'm beginning to wonder if it is oxidation or something in the gelcoat that cannot be removed.

I tried using 500 grit sand paper last year on a small area and it didn't do anything to the cloudy appearance of the gelcoat. I have to do the entire boat so I'm not looking forward to sanding but everyone on the forum has told me not to paint and there is something that will work, but I haven't found it. I haven't tried Aqua-buff that mpostgate suggested but I don't have much confidence that will work either.

If anyone has a suggestion I would be happy to e-mail you pictures of the boat if that would help.

Russ
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Old 04-04-2005, 09:59 AM
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Default RE: Power sanding gelcoat.

Russ-

It sounds like your hull was as far gone as mine was. The oxidation layer on my boat was thick enough to require very aggressive sanding. This is what I did:

1. Dry sand 150 grit with 1/4 sheet orbital finish sander
2. Dry sand 220 grit with 1/4 sheet orbital finish sander
3. Wet sand 300 grit with 1/3 sheet air sander
4. Wet sand 400 grit with 1/3 sheet air sander
5. Wet sand 600 grit with 1/3 sheet air sander
6. Compound with 3M Super Duty
7. Compound with 3M Finness-it
8. Wax with Collonite 845

Wash the hull really well in between each step to remove the previous grit and keep the sander moving all the time. It is alot of work but your hull will look new.

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Old 04-04-2005, 04:11 PM
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Default RE: Power sanding gelcoat.

ChemGuy,
Wow that sounds pretty aggressive, did you have any problems sanding through your gelcoat? How do you know you have sanded enough with each grit? Do you get all of the oxidation out with the dry sanding and then the rest is just to get out the scratches from the previous paper?
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Old 04-04-2005, 08:49 PM
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Default RE: Power sanding gelcoat.

I had the same problem,

Wash boat, sand using a random oribatal sander and 220 grit, wash boat and sand with 320 grit, wash boat and sand with 600 grit, wash boat and sand with 3M Finishing Film disks PN 00970 P800, wash boat and sand with 3M PN 051131-00968 P1200, wash boat and finish with 3M polishing pad. Wash and apply Vertglas using at least 6 coats. Althought my boat is white this should work. Still looks good after 4 years.
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Old 04-04-2005, 09:18 PM
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Default RE: Power sanding gelcoat.

Cody,
Did you also dry sand or did you wet sand all of the different grits?

Russ
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Old 04-04-2005, 09:23 PM
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Default RE: Power sanding gelcoat.

I have used the aqua-buff product. It is very good. A boat dealer that I know recommended it to me. Very little goes a long way and it leaves a nice gloss finish. I used it on a black hull. I no longer own the boat so I cannot take pictures, but it did a very nice job.
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Old 04-04-2005, 09:41 PM
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Default RE: Power sanding gelcoat.

Russ-

"did you have any problems sanding through your gelcoat?"

There were a couple of good sized dings in my gel coat that let me identify how thick it was. I kept this in mind while sanding. I went through to the glass once trying to*feather in some of my own crappy gel coat repair but that was it. If your gel coat is decently thick and you don't fall asleep with the sander against the hull you will be OK.

"How do you know you have sanded enough with each grit?"

My hull is an off-white color, more tan than white, so I sanded with 150 grit until the correct color was showing. With the remaining grits I just went until all the scratches were the same size.

"Do you get all of the oxidation out with the dry sanding and then the rest is just to get out the scratches from the previous paper?"

Yup. The oxidation was removed with the 150 grit. All the rest was to get those 150 grit scratches out.

I started with 150 because I found that it took less time to quickly sand and then step up a grit than grind away with a finer grit until the oxidation was gone. It sucked. It took forever. My hull looks brand new.
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Old 04-05-2005, 11:56 AM
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Default RE: Power sanding gelcoat.

Another option to sanding is PoliGlow. http://www.poliglowproducts.com/
I haven't used it but it might be worth a try before going the trouble of sanding the gelcoat down.

thanks, Fishing-Rod
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Old 04-05-2005, 03:18 PM
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Default RE: Power sanding gelcoat.

Since the chemist was so nice, I guess I have to be

The poli-glo or whatever it is was used by my father on his 27' Catalina sailboat. It's a 1981, and it looks brand new. The boat had serious chaulking and 2 coats of that stuff did the trick. I have no idea if it will help in your situation, but it's worth a look. The effect is quite surprising.
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Old 04-05-2005, 08:16 PM
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Default RE: Power sanding gelcoat.

Russ, I only dry sanded the hull. But I took it easy and did not put a whole lot of presssure on the sander.
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Old 04-06-2005, 04:20 PM
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Default RE: Power sanding gelcoat. (Update)

I started sanding at 8:30 this morning and I just quit at 5:00. I started out wet sanding with 220 grit and finished almost all of one side with the 220 grit. There are still some spots that are cloudy but I sanded through the gelcoat in one spot about the size of a finger nail so I think I'll leave the still cloudy parts alone.

Tomorrow I'm going to finish the port side with 220 grit and then start with 320 all the way to 2000 grit and completely finish the port side.

I can't believe how much sanding it has taken to get the oxidation out. I've been using an electric orbital sander along with hand sanding with a sanding block. My arms are about to fall off but I think I made some head way.

Russ
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Old 04-07-2005, 06:37 AM
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Default RE: Power sanding gelcoat.

Russ, I have a feeling you are using the wrong type of "buffer". An orbital buffer/polisher used for applying and/or removing wax isn't aggressive enough. You NEED to use a compounding machine that turns at a slow speed, whether two wheels or one, and work on small areas at a time. I'm just guessing about your "machine", but a 3M Rubbing Compound used with the right machine should show some great reults, right away. The 3M Finesse It II used with the same machine should make it shine. Maybe it's just the "buffer" you are using!!!
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Old 04-07-2005, 09:08 PM
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Default RE: Power sanding gelcoat.

Blue C's

I'm using an orbital with sandpaper now, not rubbing compound. I have a Makita 2 speed buffer that I've used to rub out the hull at least seven times with various rubbing compounds. With the sanding I'm having to do to get to clean gelcoat no amount of rubbing compound would have worked. I've got some places where I've had to wet sand with 220 grit paper for 20 minutes to get the oxidation out. It's like the oxidation or discoloration or whatever the cloudiness is from is deep in the gelcoat.

I'll be back it again in the morning as long as it isn't raining like it did all day today.

Russ
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Old 04-07-2005, 09:36 PM
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Default RE: Power sanding gelcoat.

damn you guys are making me tired just reading about this - try Interlux Perfection - new urethane made for rollers and brushes...seal it and be done with it....

http://www.yachtpaint.com/usa/default.asp
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