Preparing for GT27 build - questions

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piperdown
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Re: Preparing for GT27 build - questions

Post by piperdown » Wed Dec 05, 2018 4:00 pm

wkisting wrote:
Wed Dec 05, 2018 9:43 am
Eric, I just want to make sure I understood your comment correctly because there's some ambiguity in the syntax.

I think you're saying:

1. Just like other materials, graphite will not have an effect on the epoxy bond.

However, I wanted to make sure you didn't mean the other way your sentence can be read:

2. Graphite does not affect epoxy the same as other materials do; it has a different effect on the bond.

Is #1 what you meant? (If so, that's reassuring--and what I was hoping to hear). If you meant number 2, can you elaborate on how it affects it differently?
#1. Graphite only adds a hardness factor that does not impact the chemical bond with epoxy. Now there may be a situation where adding too much of an additive may impact the bond. Like adding too much wood flour to the point of "crunchy peanut butter". But with the amount of graphite there is not an issue.


Eric (aka, piperdown)

"Give an Irishman lager for a month and he's a dead man. An Irishman's stomach is lined with copper, and the beer corrodes it. But whiskey polishes the copper and is the saving of him." --> Mark Twain

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Re: Preparing for GT27 build - questions

Post by fallguy1000 » Thu Dec 06, 2018 4:22 am

Any inert additive to epoxy reduces the bond strength. This is why we don't add tons of graphite or pigments.

Acetone is not inert!

All this idea sanding increases surface is not fully true.

Epoxy sticks best to irregular surface.

If you polish a surface; the epoxy bond would be poorer.

The best bond is a wire wheel.

This is why using the lowest grit ratings produces the best bonding.

And avoiding air is better still. Avoiding air in laminates is done by working wet on wet or sanding and prefilling voids or large surface irregularities with thixotropoc mixes.

There is zero truth that secondary bonding of the same quality substrate is better.

If you have to choose bonding...

Best is wet on wet.
Next is wet on tacky.
Next is wet on rough sanded substrates, prior to full cure.
Next is wet on rough sanded substrates after full cure.
Next is wet on fine sanded substrates. (Weave fill)
Finer sanding results in progressively poorer bonds
Adding inerts is a crapshoot as well. More inert reduces bond.
Next is wet on wax, etc bond failure results. Desired in moulds.

All have the caveat of starving the work or air pockets, etc. causing problems. Always afraid of starving in my job!

Get away from the idea sanding makes for a better bond.

All the testing shows otherwise and if you try to tear apart well consolidated wet on wet work; you'll agree.
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wkisting
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Re: Preparing for GT27 build - questions

Post by wkisting » Thu Dec 06, 2018 6:02 am

Thanks fallguy. Everything you're saying fits with my understanding as well, so we're on the same page. I just wanted to make sure there isn't something special about the nature of graphite that changes the rules, since I haven't used that particular compound with epoxy (well, except once to touch up some carbon fiber kayak hatches, but that was a purely cosmetic issue). My thanks to Eric for clarifying his statement as well.

My plan will be to aim for the smoothest application of the epoxy-graphite mix I can get, and if it does go reasonably smooth with no major problem areas that concern me, I'll continue rolling on one or two more coats as soon as each preceding coat gets through the initial gelling phase (~8 hours after application). If I can get to three coats that way, sand, and then skim coat for evenness as aesthetics, that's a process I'd be fully comfortable with.

My thought at this point is only to coat to the chines, so that the bottom panels are completely coated, perhaps wrapping up the sides 1-2" just so I can ensure the chines themselves are fully coated and have a little room to fair the thickened graphite back into the side panels. Then I'll paint the side panels and transoms from shear/gunwale to chine, but leave the bottom bare epoxy-graphite which, because it is facing down, should brook the very indirect UV exposure fairly well even during prolonged storage on a trailer. My assumption is there is no point in painting over the graphite bottom because, while that would give UV protection, it will substantially complicate later maintenance to the bottom. Rather than painting it, it seems proper to leave it plainly visible on the bottom to facilitate inspection and simpler refreshing of the epoxy coating. Does that sound correct, or is there something I haven't considered here?
Wes
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My build thread is here --> viewtopic.php?f=12&t=63644

piperdown
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Re: Preparing for GT27 build - questions

Post by piperdown » Thu Dec 06, 2018 7:19 am

While I'm a ways off from putting graphite on my GF16 your description is what I'll be doing so it sounds reasonable to me.
Eric (aka, piperdown)

"Give an Irishman lager for a month and he's a dead man. An Irishman's stomach is lined with copper, and the beer corrodes it. But whiskey polishes the copper and is the saving of him." --> Mark Twain

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Re: Preparing for GT27 build - questions

Post by wegcagle » Thu Dec 06, 2018 8:31 pm

At Disney with the family, so no long response....but this I completely agree with. I shouldn’t have said increased surface area. Should’ve said roughed surface. Thanks Fallguy for keeping me honest!
Best is wet on wet.
Next is wet on tacky.
Next is wet on rough sanded substrates, prior to full cure.
Next is wet on rough sanded substrates after full cure.
Next is wet on fine sanded substrates. (Weave fill)
Finer sanding results in progressively poorer bonds
Adding inerts is a crapshoot as well. More inert reduces bond.
Next is wet on wax, etc bond failure results
.
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wkisting
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Re: Preparing for GT27 build - questions

Post by wkisting » Fri Jan 11, 2019 8:16 am

Good morning everyone! I'm planning to put the graphite/epoxy coating on the bottom of the GT27 tomorrow.

There are myriad ratio recommendations online. It sounds like less graphite = harder, less slippery finish; more graphite = softer, slipperier finish. I'm assuming for a boat this size, harder is desirable, which puts me closer to the 10%-20% graphite to epoxy (by volume) recommendations. Yes? It looks like mainly kayaks (much smaller craft) that have gone to higher ratios such as 50/50.

Plan is to use medium hardener, crank up the heat as high as I can get it inside the shelter (which raises the air temp about 30-40 degrees above ambient, so tomorrow that should get us to about 80-85 deg F), roll on a coat every 4-6 hours (which, with the medium hardener, seems to get it through the initial gel/tackiness stage to a touchable, almost tack-free surface), and do three coats by the end of the day. Then full cure for the week, and next weekend, wet sand and final skim coat with reduced graphite volume to make it spiffy.

I welcome your input.
Wes
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Re: Preparing for GT27 build - questions

Post by wegcagle » Fri Jan 11, 2019 8:44 am

Wes, I just went back and double checked my notes. I used 25% graphite by volume in the first two coats and increased it alittle to 30% on the last round (thought was to make it alittle slicker on the last coat). I never got a scratch on the bottom beaching at the lake all the time.

What I did was:
1. Mix epoxy per usual and poured it into a paint roller tray (takes longer to harden vs in a zip lock baggie).

2.Then poured 1/3 of the total graphite powder into a kitchen sift and slowly sifted into the epoxy mix to get rid of all the big clumps. (Graphite powder gets really clumpy if you just toss it in the epoxy).

3. Then mixed that well into the epoxy, and repeated until all the graphite was mixed in.

4. Rolled and tipped onto the bottom just like paint.

Good luck!!! This is one of those “Oh yeah!!” moments when you get done 8)

Will
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wkisting
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Re: Preparing for GT27 build - questions

Post by wkisting » Fri Jan 11, 2019 10:15 am

Thanks Will! That's helpful. 25% will make the calcs easy. I saw that same ratio recommended in the Cracker Larry information posted a few pages ago, but I didn't know what size boat he was referring to.

An urgent question has surfaced...

Although I don't see it mentioned anywhere in the narrative, I suddenly discovered one of the illustrations showing the rubrail also shows 2" x 2" runners (!!).
GT27 runners.JPG
GT27 runners.JPG (22.92 KiB) Viewed 193 times
There doesn't seem to be any guidance on what kind of wood, nor any other images showing whether they the run the entire hull length (bow transom to stern transom), or some potion thereof with a tapered entry... Until now, I hadn't expected to install runners at all, but this makes me wonder if they're necessary to the design--possibly for hull stiffness as well as abrasion protection. Jacques? Advice? I do worry they might interfere with ease of loading onto the trailer, but I suppose I can adjust bunk spacing to go between them if they're needed. And are they glued on, or bedded and screwed on to allow for replacement?
Wes
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My build thread is here --> viewtopic.php?f=12&t=63644

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Re: Preparing for GT27 build - questions

Post by piperdown » Fri Jan 11, 2019 11:07 am

I'm using clear pine on my GF 16. In another thread I asked about if it was supposed to be true dimensions or nominal dimensions. JM replied nominal so mine will be 3/4 x 1 1/2 rather than the 1x2 that was called out in the plans. I bought 4 8' 1x2 at a big box store and scarfed them together with thickened epoxy.

There are several ways to attach them. All of them include thickened epoxy to glue them down. Some use screws, then remove the screws and fill the holes with epoxy. Some use straps and bracing boards until the glue has set. I also seem to recall a build or 2 (when I was reviewing build threads) where they just triple coated the runners with neat epoxy and then just screwed them in place. Most of the more experienced people glue them in place.

I think a majority of folks then glass them to the hull but it's not a requirement of JM in his plans.
Eric (aka, piperdown)

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wkisting
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Re: Preparing for GT27 build - questions

Post by wkisting » Fri Jan 11, 2019 3:12 pm

It's just strange that nowhere else in the plans are the runners mentioned. If they're necessary, I think I can extrapolate their placement as they appear to be located the same distance off centerline as where the interior floor supports/stringers will go. But Jacques had originally indicated his recommendation that we lay up three layers of 12 oz. biax on the exterior hull (when 1208 wasn't available) was in order to gain thickness for abrasion protection. Now it looks like that's redundant if there are also runners (?). The runners were never mentioned. Are the runners optional, I wonder?
Wes
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My build thread is here --> viewtopic.php?f=12&t=63644

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