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  • 1 Post By Gary M
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Old 04-02-2012
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Fiberglass question

Quick question to everyone with some knowledge of fiberglassing in an old through hull. I was reading the latest issue of one of my favorite sailing magazines which happened to have a very good write up of glassing in an unused, or three, through hulls. I have read else where and it was the case in this article, that the hull should be ground out in a feathered fashion creating a concave depression that has roughly a 12:1 slope to the edges.Then consecutively increasing (or decreasing depending on point of view) discs of glass matting should be cut totaling 10-12 layers in total.

Here is the part that confused me. The article has the circles of matting being laid in with the largest diameter disc first working out to the smallest. This seems backward to me. Isn't the point of the different sized discs to get them to overlap their edges as they build up? The article seems counter intuitive, I would think the smallest diameter disc would go against the through hull opening and then the next larger, next larger, and so on.

I know this was a long winded question that I could probably find a convincing answer to if I look long enough, but I know that there are several experienced glass repair folks on Sailnet that can probably set me straight without too much effort.

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Silvio
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Old 04-02-2012
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Re: Fiberglass question

The article is correct but what you say is intuitive, in fact the first through hull that I glassed in was done as you say. Some one here I believe explained the correct way.

The first layer of glass should cover the maximum area as it is the most important one and really needs to bond well.

Start with the full sized disc and gradually get smaller until the tapered depression if fairly flush then fair it.
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Old 04-02-2012
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Re: Fiberglass question

Silvio, Though I agree with Gary M and his understanding of the proper procedure, Thanks for the question. I, too, always think that the reasonable method would be to have the greatest number of layers bonded to the original surface, but then I remember that my reasoning does not match the instructions. Take care and joy, Aythya crew
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Old 04-02-2012
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Re: Fiberglass question

When you place the largest piece first each subsequent layer bonds very well to it. I do it that way and the other reason is that any sanding will not abrade the largest piece.
I wouldn't use only mat - it has little strength. I like biaxial 1708 which is stitched roving with mat on one side and epoxy compatible. Usually only 2 or 3 layers are needed. I glass the inside as well.
After grinding the taper outside tape something over the inside of the hole and fill the hole from outside with thickened epoxy flush with the ground edge. When the inside is glassed with one layer only a bit of sanding is required and there is no reason to fair if it will be hidden.
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Old 04-02-2012
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Re: Fiberglass question

The confusion came about because in a book Casey described doing it small to big. West system directions describe it big to small.
I actually wrote to Casey and he told me his book is wrong, at least the edition I had, and big to small is the current standard.
Yes it seems backwards but for the reasons others have said it is the standard.
In truth with epoxy it probably doesn't make a lot of difference.
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Old 04-02-2012
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Re: Fiberglass question

One of the best places to get tips for fiberglass repairs and re-coring as well as many other ideas is here Northern Yacht Restoration | Tim Lackey:* One Man, One Boat at a Time
Click on "Project Logs" - he details everything he does with pictures.

Tim hasn't written a book but he is doing it every day. I don't know if he has read Casey's books - I haven't.
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Old 04-03-2012
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Re: Fiberglass question

Thanks everyone. Makes sense once you talk it through, really not what my first inclination would have been though.

Davidpm, it probably was either the book you said or an excerpt from that book that I was recalling as describing the order as smallest to largest.

Cheers everyone!
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