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Old 06-07-2020, 10:35   #1
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Best buffing compound for gelcoat?

I had to tie on a concrete wall in high wind conditions (long story, I had no other choice). I had plenty of fenders on, but there was a lot of grinding of the fenders, and now I am left with several black marks on the gelcoat (see picture attached). I can feel that at least in a couple of places, the fenders actually ground into the gelcoat. Still quite superficial, but it is there...

I have three areas like this (this one is the worst though), corresponding to three fenders

Somebody at the marina told me that it may likely be resolved just by buffing the gelcoat.

I have no previous experience with gelcoat buffing (I have some limited experience with structural fiberglass repairs/strengthening, but never in visible areas). I watched a couple of videos on YouTube, but I am still very hesitant on how this should be done.

Can the gelcoat experts in this forum help by answering the following questions?

- What is the best compound for this kind of job? I understand there are different compounds with different characteristics.

- What are the steps to prepare for buffing? Just cleaning and de-waxing the area, or do I need to sand as well? Do I isolate the area with mask tape or you are supposed to buff a much larger area?

- Better done by hand or by power tool? (I actually have access to a buffer, but I have never used it). The area is not that large, can be handle by hand if that is the easier way...

- Other tips/suggestion

Thank you!
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Old 07-07-2020, 04:01   #2
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Re: Best buffing compound for gelcoat?

Before getting into wet sanding or buffing, I would try a “Magic Eraser” (generics work fine) moistened with water. Since these contain only a fine abrasive (no chemicals released) a simple and safe way to remove a multitude of sins on board.
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Old 07-07-2020, 04:49   #3
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Re: Best buffing compound for gelcoat?

Short version - Clean it with mild soap and water, then Presta Gel Coat compound with a rotary (not orbital or dual action) buffer.
Long version - https://www.cruisersforum.com/forums...long-6469.html
This original post is from years ago, some of the products have been updated so look at later posts or search Mainesail buffing and compounding for more info.

The key to this job is follow the directions and recommended products rather than try every other option before finally following the directions and recommendations
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Old 07-07-2020, 06:04   #4
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Re: Best buffing compound for gelcoat?

As others have suggested, I would try an aggressive cleaner first. That would be one with a very mild abrasive. I have used Collinite cleaner and cleaner wax to remove marks from the white hull on my boat. Often these marks were due to hard rubbing of an unprotected fender. I have subsequently added fender covers and highly recommend them to prevent the kind of marking you seem to have suffered.

For a really serious treatment of your gelcoat, follow Mainesail’s advice.
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Old 07-07-2020, 07:31   #5
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Re: Best buffing compound for gelcoat?

I second the magic eraser, what do you have to lose?
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Old 07-07-2020, 07:35   #6
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Re: Best buffing compound for gelcoat?

Careful using ‘Magic Eraser’ over a dark (painted) cove strip..lots of minute scratches may appear..
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Old 07-07-2020, 09:05   #7
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Re: Best buffing compound for gelcoat?

Quote:
Originally Posted by a64pilot View Post
I second the magic eraser, what do you have to lose?
magic eraser works wonders have 100 of the cheap ones from amazon think under 7.00 and for tire marks and shoe scuffs and tree yuck does great even those moldy green and brown spots wash after and seal with your favorite wax
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Old 07-07-2020, 09:22   #8
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Re: Best buffing compound for gelcoat?

If Magic Eraser doesn't do a complete job-the scratches are too deep- I have had excellent results with 3M Marine Cleaner Wax & a buffer. / Len

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Old 07-07-2020, 09:35   #9
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Re: Best buffing compound for gelcoat?

If Magic Eraser doesn't do the job then I would recommend either Aqua Buff 2000 or 1000 (# = grit size) or Meguiars One-Step. JMHO
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Old 07-07-2020, 09:48   #10
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Re: Best buffing compound for gelcoat?

From fine to course grit size:

Magic Eraser
Glazing compound
Cleaner/Wax compounds like Colonite or Mother's or Meguire's
Bon Ami or Bartenders Friend
Soft Scrub
Polishing Compound
Rubbing Compound
1200 grit wet/dry
600 grit wet/dry


Try using the smallest (closest to top of the list) grit that is effective. Use a foam sanding block or similar. Circular motion is good. The finer the grit the smaller the scratches made in the gel coat. Smallest grit leaves the glossiest surface. Sometimes carefully using a razor blade like a cabinet scraper works fine for removing heavy black scuffs followed by a polish.
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Old 07-07-2020, 09:48   #11
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Re: Best buffing compound for gelcoat?

We had some nasty brown stains near the waterline, a fellow boater suggested On and Off gel (got it from Ace hardware) which worked wonders before I waxed the hull.
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Old 07-07-2020, 09:59   #12
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Re: Best buffing compound for gelcoat?

I had good luck with the Total Boat compounds from Jamestown Distributors. Total Buff then Total Shine. Worked great on getting marks out and bringing the shine back.
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Old 07-07-2020, 10:31   #13
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Re: Best buffing compound for gelcoat?

I owned and operated a boat repair facility for years--have seen this many times. I recommend thoroughly cleaning the area with something like Soft Scrub to remove any debris from fender or dock. Use heaving duty rubbing compound (3M automotive is fine) to remove fine scratches. Lightly sand what is left with 1000 grit wet sandpaper, then rebuff gently with rubbing compound. If any marks remain, determine how deep they are and are they through the gelcoat. If very deep or through the gelcoat, you will want to fill with manufacturer's gelcoat.
Should you have to fill deep scratches (gouges), first thoroughly clean surface with acetone. Tint the resin with appropriate gelcoat, catalyze, and and apply to the gouges. You can use a small piece of wax paper and plaxtic spreader to smooth the new material. Place the paper over the inlay and gently smooth with the spreader. Let this set for at least 12 hours before removing paper. After material cures (24-36hrs), wet sand starting with 600 grit wet/dry sandpaper to get the material to dimension and switch to at least 1000 for surface quality. When sanding, wrap the paper tightly around something hard and straight such as a paint stick and keep the surface and paper wet with a spray bottle. Finish by polishing with a polishing compound.
Note: sand few inches out around the area of repair to smooth the transition from the molded surface to the repaired surface--repair will/should be smoother than the molded surface. After polishing you can expect to see a brightness halo around the repair as the original gelcoat has been slightly yellowed by sunlight. If you use original gelcoat, this halo will gradually disappear over 3-4 months.
While it may be tempting and quicker to use automotive paint, paint simply won't hold up over time and was never designed for the variety of harsh conditions faced by a sailboat.
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Old 07-07-2020, 10:45   #14
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Re: Best buffing compound for gelcoat?

Here you go, good information here:

https://www.youtube.com/playlist?lis...g98Cxe6VLOq83B
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Old 07-07-2020, 10:58   #15
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Re: Best buffing compound for gelcoat?

Mequyers One Step - best product I have ever used
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