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Fiberglass repair the right way?

7K views 36 replies 14 participants last post by  chef2sail 
#1 ·
I cann't post links so:
Google search "casey fiberglass repair"

I seems pretty clear that Casy says to fix a hole starting with a piece of cloth 1/2" bigger all around than the hole. Then adding layers each layer 1/2" bigger all around for each layer.


Goto Google video and search for "west fiberglass repair"

Am I seeing this wrong. They are saying to start with the biggest piece and make each subsequent layer smaller.


Who is right?
Seems like a really major difference.
 
#2 ·
It Depends.

There is no hard and fast answer. It depends on what part you are fixing, what side you are fixing it from, how it is supported, how much stress it needs to bear, etc. etc.

When you are making a repair, the reason for the increasing size of your patches is to spread the load over as big an area as possible. The smallest piece is going to be the one in the center of the hole, so if you are fixing it from one side only, then this will be the first or the last piece that you put on.

If you are patching the hole on both sides, then you're going to start with the piece that is about an inch bigger than the hole, then lay a larger piece on top, then a larger one, and maybe a fourth one too. When that's set up, you'll fill the hole itself with a couple of pieces and the repeat the layering on the other side.

If you're fixing a hole where one side is butted firmly against something, or you have seald it, then you're going to start with the smaller pieces and get bigger as you work your way out.
 
#3 ·
Davidpm-

Part of the problem is that the order the layers go on in depends a lot on what kind of damage you're repairing and how you are repairing it. There is also some difference in the thought behind which will yield a stronger repair.

If you start with the smallest and work your way to the largest, the idea is that the patches will correspond with the existing laminate the best. The idea of starting with the largest and going to the smallest may have something to do with the fact that fiberglass has the greatest strength if the glass fibers run for a greater distance...and by putting the largest patch on first, when you sand or fair the repair, you'll still have the strength of the longest and largest patch, which might not be the case if you put the patches on smallest to largest, since you'd be sanding through the longest glass fibers.
 
#4 ·
It may worth the effort to check out West Systems website. They have alot of information on different types of repairs. You can also purchase literature and DVD instructional material that is very helpful. I have also called their tech service line to get information regarding specific projects, very helpful and patient service techs.
 
#5 ·
One thing, I would recommend MAS epoxy over West...since it doesn't have the same amine blush problems that West Systems epoxy has. The amine blush is also known to be one of the components of epoxy that causes allergic reactions.
 
#7 ·
Sailingdog, i'm not familiar with the MAS prodcuts. Iv'e used the West products due to easy local availabilty in CA, discounts plus their excellent tech service. Amine blush hasn't been a problem as long as instructions are followed.
Sailernan, I'm not sitting up straight, I'm relaxing in my bunk so maybe not paying as much attention as usual. I would however take West Systesms instruction over Casey's when it comes to dealing with epoxy.

Cheers
 
#8 ·
It does not matter that much whether You start with the big or small patch.
The most important is how the 'new' patch bonds to the old, that the caracteristics of the new patch (flexibility/hardness etc) is as close to the original as possible.
If Your boat is polyester/fiberglass, then use polyester fiberglass for repair and not epoxy/kevlar.
 
#15 ·
The most important is how the 'new' patch bonds to the old, that the caracteristics of the new patch (flexibility/hardness etc) is as close to the original as possible.
If Your boat is polyester/fiberglass, then use polyester fiberglass for repair and not epoxy/kevlar.
I agree with the first part of this post and as such, very much disagree with the second half. A repair patch is a mechanical bond, and epoxy is much stronger adhesive than polyester. The most important part is properly prepping the are to be repaired, and then use a good epoxy with your choice of glass/aramid/etc.

As to the hole repair, I have used both methods, and perfer the large patch first method. I have found that in the process of fairing, you tend to sand through much of the last piece of glass, and if that piece is the largest, you lose most of the advantages of having it there in the fisrt place. Just my $0.02.

Ryan
 
#9 ·
Sailernan, I'm not sitting up straight, I'm relaxing in my bunk so maybe not paying as much attention as usual. I would however take West Systesms instruction over Casey's when it comes to dealing with epoxy.
Was just kidding about the 'pay attention' part.

I think it's good to read some things about the way other people do things, but when it comes down to it, it's all pretty simple stuff. You need to know how to mix the goods and how long it needs to set up, but outside of that it's just logic and patience.
 
#11 ·
I've used the Casey method with great success. It makes sense to me to do it this way, because the edges of the hole must be ground out. The result is a taper leading from the good glass down into the hole. The deepest part of the hole is the smallest, so use the smallest piece of your repair patch there. As your repair gets thicker, it matches up to a larger diameter part of the taper and you use a larger diameter patch.

If I used too large of a piece of glass to patch the hole, it tends to pull up in the center if using mat, or pucker if using cloth. Then again maybe I'm just not familiar with the other technique.

John
 
#12 ·
I've used the Casey method with great success. It makes sense to me to do it this way, because the edges of the hole must be ground out. The result is a taper leading from the good glass down into the hole. The deepest part of the hole is the smallest, so use the smallest piece of your repair patch there. As your repair gets thicker, it matches up to a larger diameter part of the taper and you use a larger diameter patch.

If I used too large of a piece of glass to patch the hole, it tends to pull up in the center if using mat, or pucker if using cloth. Then again maybe I'm just not familiar with the other technique.

John
With all due respect it is the oposite of Johns discription, it does seem ass about but you start with the largest piece of cloth to make the largest possible contact with the depresion you will have ground into the hole.
Because its back to front in relation to what you would think would be the right way is what makes it easier to remember.
 
#14 ·
the first thing i see wrong is filling a circle. no matter what or how you fill it,, you will always see it, even through the best paint job. it needs to be odd shape,, take a grinder to it and put some lightning bolts into it on the outside of the O so its more like # or {} amything except a O
 
#16 ·
what haffiman is saying is, that rock hard epoxy doesnt flex the same as the poly,,,there lies ya problem and where ya cracks are going to be. so to keep that from happening you need to use what everything around the patch, is made from poly,,,,, and the mechanical bond is bout the same for poly as epoxy,,, its just that the epoxy is harder,,it doesnt mean it "sticks" any better
 
#18 · (Edited)
I really hope you don't build boats for a living. The secondary bonding characteristics of epoxy is much stronger than that of polyester or vinylester resin. That is a major reason why epoxy is generally used for repairs.

Yes, epoxy-based GRP and Polyester/vinylester-based GRP will flex and expand at slightly different rates under the same stress and temperatures, but that generally isn't much of a problem unless you've made one side of a boat in epoxy-glass laminate and the other in polyester-glass laminate.

When you're talking about relatively small patches, like filling in a 4" instrument hole or 2" through-hull hole, the differences in flex and such are not really a major consideration IMHO-especially given epoxy's stronger secondary bonding characteristics and greater tensile strength.



As for your earilier post about making the hole non-circular-you don't seem to realize that by expanding the scope of the hole more than necessary to grind out the non-circular shape you're actually damaging the existing laminate and weakening it, and effectively exacerbating any problems you'd have due to the strength and expansion differences between the patching epoxy and existing polyester resin.

BTW, the fibers in any laminate provide the greatest strength when they are fully continuous. This is why chopper gun fiberglass layup is so much weaker than using tri-axial roving-since the strands are much shorter in chopper gun fiberglass. By sanding an irregular outline around the hole, you're effectively weakening the laminate all around the hole...and since the outline is irregular, it is unlikely that you can repair that area with contiguous strands of glass in the patch. This is also one major reaons I generally like to put the largest piece of glass down first, rather than the smallest-when you're sanding the surface fair, you tend to go through the outermost layers quite a bit...and that would leave you with the shorter layers intact, but break up much of the longest fibers in the repair.

You can't have it both ways. Either you should minimize the use of epoxy, due to the difference in bonding and expansion characteristics, or you should maximize the contact area because having an irregularly shaped patch will increase the strength of the repair... :rolleyes:

Again, I really hope you don't build boats for a living or that people don't use your boats for anything serious, given what you're saying on this forum.
 
#17 ·
To add a little complication the West Systems Video shows wetting out all the layers of the patch and sticking them together on your work table, then slapping them in the hole in one dramatic moment.
I suppose if it is too thick you just peel off the last, smallest layer.
I am loathe to argue with the West people as they have been doing this a while. I wonder if the difference in style has to do with the difference between a production technique by someone with 30 years experience and a technique more in line with average skills.
 
#19 ·
um yes i do er,, did build boats for a living, and i painted too. and the people that taught me all this are the very top boat builders in the world. and when ya talking bout a small patch yes it dont matter,, but didnt the patch this thread is about end up like WAY bigger then a few inches?, and if the hole is a circle its a stronger patch then if the hole is a jagged edge? hmm what science is that?
 
#20 · (Edited)
and P.S. the only boat that i've built to come back for major repairs other then cosmetics was an apogee 55 that when it was built the dude didnt know what he wanted for port lights so we had blanks in them,, when he decided they put them in using epoxy ,, 8 years later every port light cracked,,guess where and why?, and before ya wanna insult,,, i didnt have nothing to do with the epoxy ;)
what production line did you learn from? i bet i've repaired one of em :)
and dont over exaggerate ,, putting a small 1/4 nick in that circle doesnt compromise anything
 
#22 ·
LOL... actually, physics also supports that idea... the water pressure would help hold an external patch in place, but would be working against an internally place patch, since the water would be pressing itw away from the repaired surface, not into the repaired surface. :D

BTW, I don't see where the OP (davidpm) ever said how large the patched area in question was... if you did, please quote it for me... since you said that the patch in question was significantly larger.
 
#24 · (Edited)
Working from Inside
If the damage area is small and above the waterline, make the repair from inside the hull, if possible. You are going to bevel the edge of the hole with a 12-to-1 chamfer, so if you repair a 3-inch diameter hole through a 1/2-inch-thick hull from the outside, you end up with about 15 inches (diameter) of surface damage to refinish. Repair it from the inside and you have only a 3-inch hole to refinish.<<< 15 inch hole , quoted from the casey page,,, and nowhere did i say that poly adheres stronger then epoxy i said the mechanical bond is bout same hehe ( how deep into the poly does epoxy melt into, and if it does that isnt it a chemical bond?),, just because something is stronger or does something better doesnt mean its ALWAYS the right answer,,and if your any kind of fiberglasser you know there is shrinkage and you deal with that and it ends up right,,,,,,take a 3 foot square of glass,,lay it up with poly,,, cut a hole bout say,,5 inches,,repair it with epoxy,, now take it and bend it,,,,,what flies?,, that epoxy patch does,,,,now do the same with epoxy and glass,,,fix the hole with epoxy,, bend,,, what flies??? nothing.
 
#25 ·
and i fergots bout the way the epoxy was mixed,,, all 3 guys have been doing glass work for over 30 years each,, they tried telling the owner not to use epoxy,, but he got it in his head that it was stronger so it had to be better,, and i cant imagine they did ALL 8 port lights in 1 batch of resin,, and i cant imagine they could mix it wrong all 8 times. and i know them slow old dudes didnt do it on same day.
 
#26 ·
While it may not have been mixed incorrectly each time, the person, if unfamiliar with epoxy work, may have used the wrong type of hardener or done something else, like mix epoxy in the wrong type of container, and contaminated the epoxy each time. In one case, down at my marina, a guy was using waxed paper cups to mix epoxy... with somewhat unpredictable results.
 
#27 ·
i cant say what they did,, i wasnt helping, but i do know they knew a very lot bout epoxy, and worked with it for years. as of me i've used epoxy maybe enough times all together to stick 10 boards together ( short boards) , and it was them same oldies that told me how to repair it and why it happened, then handed me a 9 inch wildcat and said cut-em out.lol the perks of seniority ;)
so when it comes to epoxy im a idiot,,and will be learning forever,, but i do know what i've had to deal with and how the "teachers" taught me to do it so i didnt have to do it again lol ;)
 
#28 ·
So what is the bottom line here?
There seems to be two basic disagreements.
1. If you have a 4" hole in a 1/4" thick hull tapered out to a 10" depression do you put in a 5" piece first (1/2" overlap) or do you put the the 10" piece first and let it belly to the bottom of the hole?
2. Are you better off using epoxy for extra strength or poly to match hardness and shrinkage of hull?

If I got the questions right I may be able to find someone with an engineering answer.
It looks like any combination will work as we have two experienced people with different takes. The bottom line may be that it dosn't matter much. Or there may be certain conditions that favor one approach over another. I just want to make sure I have the question right before I take it to the engineers.
 
#30 ·
we usually go small first, that way your largest piece is usually just mat, there basically for the fairing,,thats why we go from small to big, and because if you start from inside where the strongest glass is, you only take out a little of what matters, leaving the cosmetic (largest) outside piece last. this i think gonna turn into the " chicken or the egg" threads haha ;)
as for #2 heh,,you got opinion ;)
 
#32 · (Edited)
I asked Don Casey the question directly and got a very comprehensive logical reply. The answer is that biggest first is best but lots of people have done it the other way for a long time and it has worked OK.
As a point of reference I just watched the http://www.bennettmarine.com/store/show_product.php?cat_id=59 Bennett Marine video and they show the expert using a patch with all layers the same size "large" and just slapping it in. It left a lump around the outside edge that he just ground off.
So it looks like we now have Don Casey, West Systems and Bennett all saying about the same thing.
Also this minor flap as shown how forgiving fiberglass is as a material for repair.

>>> Don Casey Response
Your original question:
Assuming a 3" hole in a 1/4" fiberglass skin ground to a 9" depression a West video shows the 8.5" piece of repair glass being the first piece laid down while your books show the 4" piece as first and 8.5" as last.
Do you think it matters? Would one way be better in some circumstances than others?
Also some people say patches on a glass hull can use epoxy while others say it is better to use the original resin to match the shrinkage and flex of the original material and not create a hard spot. Who is correct?

Our expert's answer:
When filling a depression the intuitive order is small to large but the problem here is that we are trying to replace cut-away or ground-away fabric and the new fabric, except for the bottom piece, will only attach to the original material at the perimeter-in effect a butt joint. Laying the largest piece first maximizes the surface area of the secondary bond. After that all subsequent laminates bond to this first piece and each other on a molecular level but applying them in a large-to-small order still maximizes the mating surfaces.

In addition, when using polyester or vinylester resin, the first piece must be mat. If it is the largest piece it gives you the required mat base for all subsequent laminates. If it is the smallest piece, even if it is mat, the next layer, which will be cloth, will not have mat between it and the existing laminate beyond the perimeter of the underlying piece. This will make for a weaker bond.

If you are using epoxy resin, the order of the laminates makes less difference to the strength of the repair. Small first tends to yield a neater appearance but the void created where the larger layer overlaps the edge of the one beneath can create a void that lets the thinner epoxy resin drain through unless you thicken it. A large-to-small order avoids this. Also the relatively recent development of epoxy-compatible mat makes a large-to-small schedule using mat between the cloth layers a possibility.

Bottom line is that despite counsel to the contrary in a number of books with my name on them, large to small is usually better unless you have a specific reason to do otherwise. A new edition of This Old Boat out late next year will reflect this change in thinking and technology.

As for which resin to use, I think the better adhesion of epoxy trumps all concerns about differing flex characteristics. Here again, however, you are right to question the "experts." The fact is that some fairly recent testing show a secondary epoxy bond just 15 percent stronger than polyester. If you were thinking it was more than that, this might influence your choice of resins based on either cost or consistency with the original lay-up.
>>> >>> End Don Casey Response
 
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