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Old 29-10-2008, 15:59   #1
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Fiberglass sanding

Hi all
WE Have an older lagoon catamaran with a domed main salon roof. The old vinyl came off. I tried to cover it with FRP panels ( spent the whole hot summer), but the end result just didn't look professional. So my husband and I tore the whole thing down and are back to the bare fiberglass again. There is still some old glue, but it is somewhat flat but there are imperfections.

We decided to sand it and paint it with some sort of epoxy paint to fill in some of the imperfections. Has anyone done this? Any suggestions on how to get a reasonable surface to paint? Any suggestions on what kind of paint and base coat?

Thanks for whatever suggestions you might have

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Old 29-10-2008, 17:44   #2
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Sand & Paint

I went through a similar project last winter.

I had a glued on hull liner where the foam backing was disappearing. I pulled all the liner off and was left with foam and glue. I wanted a clean surface to apply contact cement for the new liner.

I tried many methods to remove everything, from wire wheels, which was good for the foam. For the glue and surface clean up I used a paint stripping disk made by 3M (looked like a blue puck) that fit on my polisher/grinder. It worked a treat! I had spent weeks fiddle farting around to get a square foot cleaned, and with the 3M Coating Removal Disc I completed all my removal in a day!

The Paint I used was a metal paint, along the lines of Tremclad, wiped down the surface with acetone and then painted. Did the paint 3 years ago and looks good.

My experience, good luck


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Old 29-10-2008, 19:33   #3
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If you want semi-gloss or flat white, just block sanding until everything is uniform and painting a few times will do the trick unless there are some serious blemishes.

If you want it to look like gelcoat with no waves:

Buy a long board to do the sanding of flat surfaces. 3M makes nice ones, as is their sandpaper. Adhesive backed, and comes in rolls.

Use cheap spray paint on the ceiling that has a high contrast to the color currently there. This will show the low spots, where the color remains, and you need to add fairing compound. Where there are high spots, the cheap spray paint will disappear.

Shoot various lines and zebra stripes over the area you are working, and replace as needed. I use cheap enamels, and spray from a decent distance away so the paint is practically dry when it hits.

I don't like sanding raw fiberglass... so scuff up the low spots and apply a fairing filler. I see no reason why auto body fillers can't be used inside a boat, if they are the waterproof non-shrinking variety. (IE a step or two up from Bondo.)


For the curves you will need to sand them by hand. The easiest way to go about it, is to use a high build primer. Scuff the surface real well, spray it, and sand the primer till your low spots show themselves. I use a layer of rubber from a thick rubber industrial floor mat, fun noodles, and whatever else is soft and conforming. What you don't want is to grab the sheet of sand paper with your bare hands and rub low spots in with your fingers.

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Old 29-10-2008, 19:53   #4
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For a lot of my interior I've used a Jotun product called Jotacote 605. It's a very high solids, epoxy paint. It's actually meant for painting concrete floors, so it has good filling properties and is very tough.

I rolled it on, using a normal 6mm nap roller for the first coat, and then lightly sanded (mostly to remove some of the hairs that had come out of the roller) and recoated using a 5mm mohair roller. It produces a pleasant textured, semi gloss finish similar to vinyl.

It does a good job of hiding minor surface imperfections.

It is an epoxy paint though so it shouldn't be exposed to direct sunlight.

There are other brands of concrete paint available that aren't epoxy based, some are water based, and would probably give off less toxic fumes when wet, but I've never used them.

On my ceiling I sprayed a satin polyeurethane paint. That required a great deal more surface prep to get an acceptable finish though.

Some pics here:
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Old 29-10-2008, 20:23   #5
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The pictures look great. What kind of surface prep did you use on the ceiling? Did you get a spray gun or does the paint come in a spray can? Your ceiling is exactly how I wish mine would turn out. Did you find something to trim the windows with? Sorry for so many questions.

Thanks a bunch
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Old 29-10-2008, 20:46   #6
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Well thanks, it took a LOT of work! I had some fibreglass tapes to fair in, using epoxy and Q-cel bog, then sprayed with highbuild paint with some Q-cel mixed to thicken it, a couple of times, before a final application of straight highbuild, then the topcoat.

In between there was HEAPS of sanding. Difficult work too, sanding overhead, especially inside the compound curved areas. I don't think there is any easy way of doing it (unless you pay someone else). I just wrapped some foam rubber in sandpaper and went for it. (Wear gloves or you lose skin). On the flatter bits I used a random orbit sander.

I don't know what your surface is like, it might need more work, or hopefully much less....

The topcoat I used is Jotun Imperite 300, with a de-glossing agent added. I've heard talc works as a de-glosser, but never tried it. I sprayed it on, (I'm building the boat so I have a compressor) it's a 2 pac paint so it probably doesn't come in aerosol packs.

I shouldn't need anything to trim the windows with, it's a tidy fibreglass edge, and it took the paint fine.

Good luck!

Cheers, Alan.
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Old 02-11-2008, 08:15   #7
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I wouldn’t spend much time at all sanding the glass, other then roughing it up.
Get some filler like bondo (there are some specifically for fiberglass) and some of those plastic “putty” knives…..a little more time applying the putty will pay dividends when it comes to sanding.
Wet sanding will save a fortune in paper costs.
Most paint is an expensive and very poor filler.

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fiberglass, sanding

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