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Old 04-10-2013, 19:17   #16
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Re: Fill or Glass?

Been the glass guy that has kept a fleet of Shamrocks working the last 11 years for an assistance towing firm....hard use..more tham even many "self proclaimed" pros here would ever see...

Yet Minerat is right on again....despite his detractors....

It's a good chance that the gaps/chunks you are talking about could just be filled with "Kitty hair" if you don't leave the boat in the water all year or a vinylester short strand chop repair paste and be done with it post haste.....as Minerat recommended with a "quick but realistic" repair.

Unless you are showing signs of damage in the interior...there was a boatload of filler and fairing used n Shamrock hulls that isn't structural at all along that hull joining seam....so all you are is replacing the filler and additional strength is not required.

No harm in using epoxy as a filler or on small tape job...but not really require either....unless there is more extensive damage not noted so far.

I reptaired the entire first 10 feet of a 26 Shammie that was crushed by a 80 foor crane barge and tug....they slap back together just fine with almost anything.
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Old 04-10-2013, 20:01   #17
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Re: Fill or Glass?

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Originally Posted by shamrock View Post

I don't understand why polyester is less time.

Numerous reasons. First, you can't use CSM with epoxy unless you get special hard to find CSM with an epoxy friendly binder instead of starch. Usually you must buy by the roll. Second, for a size able epoxy layup like this you generally can't get away with Fast hardener. This means it takes overnight for the repair to cure. And you may need to lay up twice. Third, you can't fair an epoxy layup with anything but epoxy. This means every time you trowel on some more filler for fairing, and it will take several applications at least to fair a stem, you must wait at least an hour, usually much more for it to cure to the point of sandability. Vinylester premium filler takes ten minutes, five with a heat gun. With epoxy, you must custom mix each batch, first mixing the resin and then thickening it. This takes time and creates wastage. With poly, you ladle it out of a can, catalyze it and go. Poly/vinyl ester generally sands easier too, using less grit and less time. I could do your stem fully faired in less than 8 billable hours for sure. Try it in epoxy and tell us how long it takes, please! Poly also allows the use of certain tricks. In this case, I would back grind and clean up. The wet out with poly resin, and apply some thixotropic resin to the big low. Then take 24 oz. woven roving cut to length and pull individual tows out of it. This gives you uni yarns. Apply into the thixotropic in the low until close to fair. Then apply a couple of matts over the top and tapering onto your back grind. Use a two roller technique, rolling both sides at once. This will give a surprisingly fair repair with a bunch of vertical uni tows laid on the stem, which will really beef it up in case of impact at the waterline. You can try something similar using epoxy and peel ply instead of matt, but good luck replicating the same effect! Then grind fair, and apply vinylester premium filler for fairing. Designed for below the waterline use, just in case. Fairing the profile of a stem right is a real bitch, you will need numerous applications and lots of flexi long board.
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Old 04-10-2013, 21:10   #18
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Re: Fill or Glass?

My opinion after briefly reading the many already posted, is to determine as one said- exactly what you have there as far as hull thickness. If in fact it is a split mold then the bulk of the layup is inside and little structure is lost. If not the case, then more glass work, maybe inside if handy to prevent undo cosmetic work. Bottom line is the epoxy is very good bonding, does not shrink like polyester but can be thickened with Chopped strand and microballons to make a very strong putty and as an extra precaution a bit of glass cloth over the top several inches on either side of the gouge. These are all judgement calls. Professionals have a way of looking at the situation and if good at structural glass (most aren't) and not just cosmetic, will get the result you need.
I am not blowing smoke, I have fixed many boats.
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Old 04-10-2013, 22:14   #19
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Fast curing epoxy

Minaret or anyone, at the risk of going slightly off-topic I'll ask why Epoxy Putty sticks can, after mixing, be sanded within 15 minutes. (Note I am not suggesting use of epoxy sticks in this repair; just a general question).

When I mix my own epoxy filler, it takes 6-8 hours before I can sand.

Is anything added to the epoxy, or is it chemically a different epoxy, that it can fully cure in minutes rather than hours, while still adhering very well and being fairly strong (eg. Marine-Tex putty seems quite good)?

Or is it simply much inferior to normal liquid epoxy resin made fillers?
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Old 04-10-2013, 22:47   #20
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Re: Fast curing epoxy

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Originally Posted by Marqus View Post
Minaret or anyone, at the risk of going slightly off-topic I'll ask why Epoxy Putty sticks can, after mixing, be sanded within 15 minutes. (Note I am not suggesting use of epoxy sticks in this repair; just a general question).

When I mix my own epoxy filler, it takes 6-8 hours before I can sand.

Is anything added to the epoxy, or is it chemically a different epoxy, that it can fully cure in minutes rather than hours, while still adhering very well and being fairly strong (eg. Marine-Tex putty seems quite good)?

Or is it simply much inferior to normal liquid epoxy resin made fillers?
There are tons of chemical variants of epoxy for different conditions. The usual resins have either a fast or slow catalyst that allow working time from a few minutes to an hour or more depending on temperature. Other types are 5 minute and they aren't kidding. Some will work underwater others In oily conditions. The more exotic formulations are usually only available in bulk quantities and only from commercial suppliers. The genius of the Gougeon brothers was not in the chemistry but packaging it in smaller quantities and in easily measured dispensers. In short, good marketing.
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Old 04-10-2013, 22:49   #21
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Re: Fast curing epoxy

Quote:
Originally Posted by Marqus View Post
Minaret or anyone, at the risk of going slightly off-topic I'll ask why Epoxy Putty sticks can, after mixing, be sanded within 15 minutes. (Note I am not suggesting use of epoxy sticks in this repair; just a general question).

When I mix my own epoxy filler, it takes 6-8 hours before I can sand.

Is anything added to the epoxy, or is it chemically a different epoxy, that it can fully cure in minutes rather than hours, while still adhering very well and being fairly strong (eg. Marine-Tex putty seems quite good)?

Or is it simply much inferior to normal liquid epoxy resin made fillers?


Yes, totally different animal. I use a lot of G5 five minute epoxy too. But you could never fair with it. The problem is in the very high exotherm temps of epoxy. Even using standard Fast hardener, it can be difficult depending on ambient temps to apply a batch of any size before it starts to kick due to shared exotherm temps. Poly does the same thing, but doesn't start to exotherm until much later in the cure cycle. You can also use different types of catalyst for different types of cure cycle with poly, and gel times off the chart are very accurate. I often mix two quart batches when doing a poly layup, and still get an hour and a half of working time on a thick layup. It's kicked and ready to grind another hour or so later. Try the same with Fast hardener and you'll waste a ton of resin kicked in the pot and blow a layup. Use a slower hardener and you must wait overnight, and probably will miss the chemical bond window for a slick.


Note also that "epoxy" has become a very flexible term in the commercial sense. I've seen all sorts of products labeled and sold as epoxy which were not, including vinyl esters, isocyanates, and methacrylates. Even many epoxy resins and barrier coats are a "modified epoxy", which can mean many things.
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Old 05-10-2013, 12:26   #22
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Thanks. The other area I am worried about is the fiberglass exhaust tube coming out of the transom. It looks like it was built up with a ton of gel coat and it has spider cracks all around down to the fiberglass. Are there any best practices on how to build up around the tube and fair in a way that won't crack down the road?
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Old 05-10-2013, 14:58   #23
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Re: Fill or Glass?

I think this is one area where a small epoxy fillet with a couple layers of glass tape may be best if you are going to paint over it...seems like the epoxy doesn't crack and separate as I occasionally have seen with what I guess is just polyester slathered in.

If enough protrudes that you can get some surface area to work with...no reason why a long strand polyester filler like kitty hair wouldn't work also....but prep would be the key there.
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Old 05-10-2013, 20:12   #24
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Re: Fill or Glass?

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Originally Posted by psneeld View Post
I think this is one area where a small epoxy fillet with a couple layers of glass tape may be best if you are going to paint over it...seems like the epoxy doesn't crack and separate as I occasionally have seen with what I guess is just polyester slathered in.

If enough protrudes that you can get some surface area to work with...no reason why a long strand polyester filler like kitty hair wouldn't work also....but prep would be the key there.


This is another case of a place where it's very common for the builders to glass the tube in on the inside, with only bondo on the outside seam. Common repair. If it protrudes, then it's easy. A little quick grind and glass will do it. Otherwise, the only really permanent fix is to grind the inside of the tube as well with a flapper wheel, and glass from the transom to the inside of the tube. As long as you use glass instead of just filler, either epoxy or poly will do just fine. But it sure is a lot faster and easier to use a couple of matts with poly, rather than using epoxy and boat cloth. That's really all it needs. PITA to fair the inside of the tube.
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