Hi,
I'm going to try and repair my fin which has the bottom 2 cm mostly missing. I think I may have success because of the way it broke, which left behind a reasonable amount of material to overlap/glue on to.

One person recommended that I use carbon cloth. I bought a bit but I've never worked with carbon before and I was surprised at how big and loose the weave was. Maybe there are other carbon clothes better suited to this job, I didn't have a lot to choose from. I'm quite doubtful it's what I should use. It's either that, some tight weave 4oz cloth, looser weave boat cloth or some mat cloth. Any suggestions?

The tip isn't that critical, you could use almost anything. The only factor is wear, carbon isn't that good at abrasive resistance, so if you regularly run into the bottom glass would be better. Probably the best job is with the 4oz glass.

If it was any more than 2cm, and it's a carbon fin, you probably should use carbon.
Io fix a break, I'd tack it together with 10min epoxy. then grind one side back close to the centre line. lay that up, when cured, turn fin over and do the same to the other side.

I don't understand the bottom broken bit, mentioned is 2cm. Are you ::re - constructing that 2cm with material?
try talking me through it again

boardlady.com/finrepair.htm

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forceten said..
I don't understand the bottom broken bit, mentioned is 2cm. Are you ::re - constructing that 2cm with material?
try talking me through it again

Op did you go away

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forceten said..
I don't understand the bottom broken bit, mentioned is 2cm. Are you ::re - constructing that 2cm with material?
try talking me through it again

Sorry, I got really busy with work the past week...

A picture is worth a thousand words. Or something like that. My plan was to support the fin on the underside with some play-doh (modeling plasticine), build up the layers on this side, then flip it over and build up the other side. But I somehow need to get the surface of the plasticine flat. Or I could put a thin leveling coat of epoxy on the underside before I build up the glass.

Not a bad idea, but I still reckon to tack it first, rather than do a full on lay up. That way, if you've judged the angle wrong, it's easy to pull apart and start again. Also you can grind both pieces while they are together, getting a nice smooth surface for glassing.

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decrepit said..
Not a bad idea, but I still reckon to tack it first, rather than do a full on lay up. That way, if you've judged the angle wrong, it's easy to pull apart and start again. Also you can grind both pieces while they are together, getting a nice smooth surface for glassing.

I didn't understand you at first but I think I do now. What would you suggest for grinding? I have an angle grinder but I don't believe I can grind a flat surface with the any kind of precision. I have a belt sander that a could maybe clamp to my workbench. I can't imagine the tacked on piece will withstand much side force though.

thanks

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shmish said..
What would you suggest for grinding? I have an angle grinder but I don't believe I can grind a flat surface with the any kind of precision. I have a belt sander that a could maybe clamp to my workbench. I can't imagine the tacked on piece will withstand much side force though.

thanks

Sorry, I'm getting old and stupid, should have said "sanding". It's just that I use a small right angle grinder with a sanding pad. A fresh 80 grit sanding pad will remove material very quickly without using very much pressure. And it's easy to get a concave curve happening, so it's deeper at the break, and tapering back out to the original surface over about 2 or 3cm on each side.

Why not support it with something flat underneath like plastic masking tape, wont stick to the resin too.

If I was doing a fin that had that much missing, I'd be doing a bit more work first. Its a lot to replace and just filler won't do.
It needs a bevel sanded first so you don;t end up with a basic butt joint that will snap off. Sand a bevel up at least 3cm on both sides, then tape one side with 5 or 6 layers of plastic tape and lay up about 10x layers of 4oz.
Tape needs to be peeled back at the bevel of course, then gently flattened down again
After that's set, build up with some JB Weld or similar and sand back to be a bit lower than needed, now another 10x layers of 4oz.

Sand to shape.

Basically the board lady method but with (1) some support as its so big (2) some strong fill in the middle to avoid the pain of 40 layers of glass.

As to sanding, much prefer finer grit and fast. a sanding disc with 120 in angle grinder and fin clamped to bench will enable you to shape it by eye pretty fast and accurately