Fibreglassing tips for a good finish?

For the gel coat, once the GRP has been built up paint gel coat on (over thick!) and cover with parcel tape in multiple strips - do not worry about being too neat at this stage...

Then, when the gelcoat is cured, instead of sanding, use a very sharp cabinet scraper. This has the advantage on modern GRP where the gel is sooo thin that the sanding of the repair can cause damage to the existing gel, as it can be more accurate in the only area being removed. If the cabinet scraper is really sharp you can go straight to cutting compound to get the gloss finish, however, any "nicks" in the cabinet scraper will then need wet & dry then compound.

This was how we used to maintain the Norfolk Broads Hire Fleet when I worked on the yard, was quick and easy..

Good Luck

Jon
 
Sounds like the problems I've had with car panels. I used flexi metal grill as a backing and then built up the surface with cloth and resin,finishing off with gelcoat/ sanding. There are supplies in Halfords which are cheaper than boaty bits and better at finishing off.
 
GrahamM376 said:
What happened? ground loop?
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Lad flying in the junior nationals went in to a field and clipped a haystack. Ground loop folded the fuse behind the wings and popped the wing skins in several places' amongst other things. I bought the wreck, trailer and instruments for a grand, spent about 300 hours rebuilding her and flew her for two seasons. All told she only cost me about £3000.

I got a LOT more when I sold her on and she's still a competitive club class ship 12 years on.
 
The 2 key challenges are matching the gelcoat colour and finishing it imperceptibly. I don't think inexperienced amateurs can do this. Why not carry out the structural repair, leaving the patch very slightly recessed, then pay a GRP repair guy to finish it? There's a guy who often works in my marina who does absolutely unbelievable things with gelcoat - he did some on my old HR and it was a truly invisible repair. But it's a huge skill which reflects many years of experience.
 
pvb said:
The 2 key challenges are matching the gelcoat colour and finishing it imperceptibly. I don't think inexperienced amateurs can do this. Why not carry out the structural repair, leaving the patch very slightly recessed, then pay a GRP repair guy to finish it? There's a guy who often works in my marina who does absolutely unbelievable things with gelcoat - he did some on my old HR and it was a truly invisible repair. But it's a huge skill which reflects many years of experience.
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Yes, the glass bit is easy compared to the finishing work and I lack the patience and skill to do an invisible gel repair. The task nimbusgb took on is amazing, I've done quite a few smaller grp glider, car and boat repairs but wouldn't even consider tackling a job like that!
 
If they are in the coaming with a void behind why not enlarge them a bit to an oval or rounded end rectangle and mould two boxes to go behind them to form a couple of open coaming storage lockers for winch handles sunglasses or similar. You could even put your replacement speakers in there at the back or set in to the top. You would need to tidy up the edges of the apertures but there are plenty of moulded plastic lippings available for that situation if you do not get a good enough gel coat edge.
 
Quandary said:
If they are in the coaming with a void behind why not enlarge them a bit to an oval or rounded end rectangle and mould two boxes to go behind them to form a couple of open coaming storage lockers
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Because they would look a bit silly above the existing open coaming storage lockers.

Pete
 
Quandary said:
Sorry, I had not noticed those, silly me. I will keep stum the next time.
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Sorry - I just get a little frustrated with the standard forum habit of sidestepping the question the OP originally asked and telling him he should do something else instead. It's reasonable when the original proposal is clearly stupid, but I don't think "how do I get a good finish when filling a hole in fibreglass" falls into that category.

Pete
 
Hopefully an answer to the actual question, although of course for you to judge whether it might work for you.

I assume that you have got hold of some 2-part Polyester gelcoat repair paste of the exact colour match - otherwise your proposal of filling proud and sanding back wouldn't work. But instead of over-filling and sanding back have you considered building it up in several layers?

After the structural repair is done, put a layer of gelcoat on and smooth it as best you can so it's flush but not proud near the edges, and almost certainly sunken-in towards the middle. Let it harden, or nearly so, and apply some more. All the time don't let it get proud, and if it does scrape off (I like the cabinet scraper suggestion). If there's a void, don't worry, just come back to it once the current area is hard.

The advantage you have over the professional is a licence to do it in multiple small goes - far too expensive / time consuming an approach for a professional, but fine for a DIY job. It might need a bit of sanding eventually, but not so much that it's onerous.
 
jdc said:
I assume that you have got hold of some 2-part Polyester gelcoat repair paste of the exact colour match - otherwise your proposal of filling proud and sanding back wouldn't work.
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I have the remains of a five-litre bucket of white gelcoat :). I did a complete rebuild of the binnacle structure last year, so most of it is new gel, but there's a point near the bottom where it blends into the old. The change is visible, but not glaringly obvious, and that's the standard I'm willing to accept for this job.

Pete
 
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