How to fill a skin fitting hole properly?

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jollysailor17

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I would like to know once I have removed a redundant skin fitting from my fibreglass hull, how I can fill the hole so that it is strong and waterproof and also smooth enough on the outside not to show?

Look forward to your replies. Many thanks.
 
Not an easy job I'm afraid.

If you are experienced with using GRP it is quite do-able but if not; go to your nearest GRP specialist.

Let me know if you are happy using GRP and gel-coat and I'll ttry and give you some pointers.
 
IIRC the method most often taught is to chamfer the hole so that it is wider at the outside and then cut discs of random matin graduated sizes to fill the hole. brace a board over the inside to work against, lined with polythene to avoid it sticking, and then start laying up from the outside. However, the largest patch is fitted first so as to get a good grip on the bevelled edge and then the others in "reverse" order. Final fairing is done with resin filled with glass spheres or colloidal silica.

If you're unsure of how well your handiwork will stand up to the challenge, you could always put an oversize patch on the inside afterwards.

Mind you, I used to crew in a boat with an aluminium patch epoxied over an old hole...

Rob.

P.S. Companies like West Systems publish lots of advice on such jobs - take a look at their websites.
 
Hi
I used to sail a wooden boat but now have my first fibreglass boat, so have no experience whatsoever working with fibreglass, epoxy and all things sticky! However, I can usually turn my hand to most things, so feel okay about doing the repair myself, once I know the drill.
Thanks for all the links, I will take a look at those. A chap in the boatyard reckoned I should use polyester resin and matt, as the boat is built of grp back in 83. Is that correct, or should I use grp matt circles and epoxy?
 
jollysailor17 said:
A chap in the boatyard reckoned I should use polyester resin and matt, as the boat is built of grp back in 83. Is that correct, or should I use grp matt circles and epoxy?
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Some people reckon that epoxy sticks better to old polyester than new polyester will. I'm not sure whether that's true, and I happily fill holes above the waterline with polyester, but I'm not sure which I'd use for a major hull repair.

What you should not do is use conventional stranded glass mat with epoxy. It's held together with a binder that dissolves in polyester resin but doesn't in epoxy. For epoxy you need to use woven mat or tape - if it's anything else make sure it specifically says it's ok for epoxy.

Pete
 
I have a similar job on the horizon but its about a 2¼" diameter hole.

I am thinking of using epoxy

It will make a better bond with the old GRP than polyester
and it wont need a gelcoat to make it waterproof.

But it needs a special glass cloth , not the chopped strand mat that one might use for polyester resin.

Also epoxy must be accurately mixed . Precise proportions of resin and hardener are not quite so important with polyester.
 
The experts agree that epoxy has much better adhesion to polyester that is not green as it is when still in the mould. Biaxial roving is a good choice and is what I use for this type of job. 1708 is stitched roving with epoxy compatible mat on one side. It is strong and thickness builds faster than with lighter cloth.
The hole should be ground to a 12 to 1 taper inside and out. Here is a good diagram showing the detail from West.
 
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If it's below the waterline, get it done by an expert, with a guarantee. You could do it yourself, but it may end up looking terrible, the laminate will probably be full of air pockets, it could leak or allow water to penetrate the surrounding matrix and it will take a lot of time to get a perfect finish - definitely not the ideal job for first use of glass and resin.
 
srp said:
I thought this was the Practical Boat Owners forum?
Do it yourself, there's very little skill involved, just common sense.
Some more information here.
Click to expand...

Brilliant.

I have saved that for future use.

Now I know exactly how I will be repairing the hole left by the old Ball-Hed when I remove it.
 
srp said:
I thought this was the Practical Boat Owners forum?
Do it yourself, there's very little skill involved, just common sense.
Some more information here.
Click to expand...
Hi SRP
Thanks for the link to the article on the Corribee website. It all made sense except Fig.1 Can you explain why the hole is chamfered from the inside and the outside?
Your link to Newlands Tech was interesting but I could not see the relevance. Did I miss something. I agree with you about the Practical Boat Owner forum, that is why I posted here in the first place as I like to do as much on the boat myself, as possible.
 
The chamfering gives you a wide contact area for the bond to form on against the old material. It also means no sharp edges for stress loading in the final layup. A chamfered plug is unlikely to push through the hole since its bigger than the hole. A newly laid up plug inside and out has a strong chemical bond in the centre patch bonding the 'yoyo' patch together so the inside stops the outside from dropping out or being pulled through and the outside plays the same game with the inside.
( did )

the sketch in mitiemp's post describes the cross section perfectly. If you are using polyester resin ( perfectly acceptable ) I would ( did ) leave out the epoxy puck in favour of forming the chemical bond between the inner and outer patches.
 
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jollysailor17 said:
Hi SRP
Thanks for the link to the article on the Corribee website. It all made sense except Fig.1 Can you explain why the hole is chamfered from the inside and the outside?
Your link to Newlands Tech was interesting but I could not see the relevance. Did I miss something. I agree with you about the Practical Boat Owner forum, that is why I posted here in the first place as I like to do as much on the boat myself, as possible.
Click to expand...

The hole is chamfered to give a good mechanical bond (I suppose in the unlikely case of impact or pressure from either side), and it also exposes a large area of clean grp for the epoxy to bond to. The method was detailed in PBO some time ago by someone (maybe Jake Kavanagh???) who went on a West Systems 1 day practical training course. The method has since been followed by several people I know,me included, with no problem. I can't claim any credit for the idea of doing the lay-up on a sheet of polythene, but it is an excellent way of doing patch repairs - especially those in awkward, difficult-to-reach places in the depths of a locker or bilge.
The Newlands Tech link is a rather blatant link to my day job - sorry if it wasted your time :o

Edit: ...and I see that Nimbus has already explained it all perfectly!
 
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jollysailor17

Have a go yourself, if you don't try, you'll never know if you can do it. The video clips on youtube are excellent, very self explanatory, and if you can follow their way of repairing the fibreglass, then you wont have any problems.
After you have completed your first patch, you'll be wondering what all the fuss was about.

Cheers Stevie.
 
I was taught to tape a mirror coated in wax on the outside and repair it from the inside, start with four coats of gell-coat on the mirror face followed by matting (weave) with resin, when finished you can remove the mirror and finish any missed bits with GRP filler then compond and wax.
As already said you have to bevel the edges first.
Done it a few times even under-water and was very pleased with the result.
 
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