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martin.langhoff

Remove thin gelcoat layer -- over CF

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I need to remove gelcoat-over-CF (and some glass) on a patch of about 1m by 5cm. Gelcoat layer is thin (1mm or less), fire engine red :-)

Right now, I'm using a circular wire brush thing on a drill, seems to take out the gelcoat fine, if a bit slow, and preserves the CF. Spots of glass (some parts have layers of glass, scarfed...) sand easier than the CF, so I've eaten into a couple of glass spots. The process leaves some gelcoat residue and unevenness, I'll use a disc sander, with a small disc, later.

I need to preserve the CF and glass layers, apply extra layers to reinforce.

Is there a better, faster way?

Also, is it reasonable to do it 'wet' to reduce the amount of gelcoat/cf/glass dust? Even with protection, I'd rather not have a cloud of it around me.

 

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My Bosch 6” sander and Fein vacuum keep the dust down

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Yeah I'd just use a RO sander with 80 grit discs. Wire brushes will eat through without taking all the gelcoat and will get into the carbon. Just cheat and tilt the sander at a shallow angle.

Or get a detail sander and lots of spare sanding pads.

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What you need is a regular 4 1/2 inch angle grinder with an AVOS disc set up, they look like this. 

Use a 60grit disc, dont go pussy and use anything less. The great feature of these is when they are spinning at 10,000RPM the holes let you see the surface underneath and with a little bit of practice you can use them to remove 1 later of paint at a time. 

If I had time I would put up a vid showing how good they are but the bar at the YC is about to open.

Screen Shot 2018-08-29 at 3.37.34 PM.png

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4" grinder with a basic disc sander kit or one of the newer more expensive style ones  like Mitre cuts is the perfect tool for composites. We call them detailers. As others have mentioned a good RO sander like a Bosch or Festool with the rotary cut switch will also do the  trick. It sounds like you have very little gelcoat to remove 50mm x 1000mm. Any random orbit sander would work fine. Stop using the the wire brush. It will eventually start tearing up the fibres. Those things are ment for removing paint or rust off of metal. 

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5cm wide by 1 meter long?

I would rip a hard foam sanding block down to 4cm, and use 40-60 grit sandpaper alternating scratch patterns and occasionally skewing the board to touch both borders.  Hard backed "inline paper" that is sold in 16 inch sticks works well, on a 4-5 inch long sanding block.  An air hose helps to blow the sanding dust out of the paper, but if not a pass with a 2 inch chip brush that has the bristles cut down to a 1/4 inch or so works too.

Just work it by down a foot or so at a time, and it'll go pretty quick, 3-4 inch long passes back and forth with a lot of pressure instead of speed.  Once you see your fibers, leave a bit of a haze of red to them so you don't have to get destructive to prep for your next structural layup. 

 

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