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Old 13-09-2015, 22:38   #31
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Re: Lightweight but strong backing material

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Originally Posted by Azul View Post
Another interesting point is that water intrusion to the core can spread great distances, especially if grooves were cut into marine plywood to help "bend" it, for example in the roof of the coachroof which is typically crowned slightly.
I have found that to be very true...found another port that was leaking where the water had migrated a significant distance before finding its way out... rotting everything in between.

I'm having significant issues finding marine plywood in St. Augustine without having to pay marked up marina prices. Closest location is in Jacksonville, so that means renting a car and driving up there. Not far away but doubles the cost of the material.

Someone said to check out the St. Augustine Marine Heritage Foundation by the lighthouse as they may have a lead on what I need. They build wooden boats there.
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Old 14-09-2015, 13:03   #32
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Re: Lightweight but strong backing material

I found a place in St, Augustine that carries the marine plywood.

How can I tell the difference between marine ply and the exterior stuff?
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Old 14-09-2015, 21:10   #33
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Re: Lightweight but strong backing material

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That article from West pretty much disproves your point Lojanica. Yes you can thin epoxy but it changes the characteristics and there is no need to do that.
Not really. CPES is just thinned epoxy. The West article needs to be read carefully. They didn't do a single coat of thinned let it dry for several days then a single coat of regular.


Anyways,

The original poster is on a budget. Had legitmate questions re: Cabin top sandwich port hole construction and I threw a few things out which I still maintain would work well. CPES is expensive!!! You can buy good quality epoxy and carefully thin it apply it to good wood and have a great result and save a few bucks.

Granted as many have said you can just buy the best follow the instructions on the can and have a good result too.

Just trying to help. Hopefully the discussion and posting of this nonsense helps the original poster and others who have similar projects.

Cheers
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Old 14-09-2015, 22:14   #34
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Re: Lightweight but strong backing material

It's pretty simple--never thin or contaminate epoxy with anything not specifically recommended by the manufacturer.
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Old 15-09-2015, 06:54   #35
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Re: Lightweight but strong backing material

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Originally Posted by zboss View Post
I found a place in St, Augustine that carries the marine plywood.

How can I tell the difference between marine ply and the exterior stuff?
Marine ply and exterior ply both use waterproof glue. The real difference (assuming the type of wood used is the same) is that marine ply does not have any voids in it.

Frankly, for the purpose you are using it, I would be just fine with exterior ply.

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Old 15-09-2015, 07:53   #36
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Re: Lightweight but strong backing material

If you're gonna beat a dead horse might as well make hamburger.

Real men get in line at the retail store and pay full price.

I think these discussions are a great tool to understanding the tools in our roll around carts.

Many an epoxy was ruined by adding fungicides, thinners, and solvents.

Many a core have been ruined by trapping moisture.

Understand the issues and create better solutions.
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Old 15-09-2015, 15:37   #37
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Re: Lightweight but strong backing material

A lighter and easier to work alternative to g10 (not as good for thread holding or as stiff/backing plate). Superior to plywood for core in almost every way.

Baltek Airex PXc Boards
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Old 15-09-2015, 17:06   #38
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Re: Lightweight but strong backing material

There's been a lot of false information on this thread about plywood.
1. Marine and exterior grade plywood uses the same glue.
2. Plywood is made with many different types of wood, this applies to both marine and exterior grade. Pick a wood that is suitable for your use.
3. As Mark said above, the difference between AB (high grade exterior) and AA (marine) plywood is that voids are allowed in the AB but are not allowed in the AA. Voids are almost always visible on the edges of the sheet. So, if you can find a sheet of AB exterior which is void free, you have found the equivalent of the marine grade, for a lot less money.

Note - both marine and exterior grades are made by a number of different companies and can feature a different number of plies. The best plywood has equal thickness for all plies and the number of plies is large, typically 5 plies for 1/2", 7 plies for 3/4" would be considered a large number of plies.

I've been using some Chilean pine plywood, AB exterior grade, beautiful stuff. Most sheets have no voids, they have high numbers of plies and are as well made as the marine grade I've worked with, and I've bought truckloads. And it's cheap, and lightweight, which is good for what I'm building with it. So judge the wood by the quality of the sheet you'll be buying.
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Old 16-09-2015, 06:25   #39
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Re: Lightweight but strong backing material

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Originally Posted by Pauls View Post
There's been a lot of false information on this thread about plywood.
1. Marine and exterior grade plywood uses the same glue.
2. Plywood is made with many different types of wood, this applies to both marine and exterior grade. Pick a wood that is suitable for your use.
3. As Mark said above, the difference between AB (high grade exterior) and AA (marine) plywood is that voids are allowed in the AB but are not allowed in the AA. Voids are almost always visible on the edges of the sheet. So, if you can find a sheet of AB exterior which is void free, you have found the equivalent of the marine grade, for a lot less money.

Note - both marine and exterior grades are made by a number of different companies and can feature a different number of plies. The best plywood has equal thickness for all plies and the number of plies is large, typically 5 plies for 1/2", 7 plies for 3/4" would be considered a large number of plies.

I've been using some Chilean pine plywood, AB exterior grade, beautiful stuff. Most sheets have no voids, they have high numbers of plies and are as well made as the marine grade I've worked with, and I've bought truckloads. And it's cheap, and lightweight, which is good for what I'm building with it. So judge the wood by the quality of the sheet you'll be buying.
There seems to be quite a bit of misinformation in your post. I can't find any evidence other than hearsay that the glue in exterior plywood is the same as the highest quality phenolic glues used in marine plywood.

But I have found citations that using PINE plywood is bad news for boat building. Apparently it doesn't take resin well and lacks stiffness among other down sides. One writer said it would be great for building a bench around your fire pit, but not for boat building.

That's what I like about this forum, you get lots of opinions which stimulates discussion and then you have to read for yourself and make up your own mind.
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Old 16-09-2015, 06:33   #40
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Re: Lightweight but strong backing material

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Originally Posted by estarzinger View Post
A lighter and easier to work alternative to g10 (not as good for thread holding or as stiff/backing plate). Superior to plywood for core in almost every way.

Baltek Airex PXc Boards

This stuff is $96 for a 2x4' panel that is 1/2 inch thick. I could make my own panels from fiberglass and poured thickened epoxy much cheaper than that from stuff I have on hand and not have to pay shipping.
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Old 16-09-2015, 06:44   #41
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Re: Lightweight but strong backing material

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Originally Posted by Azul View Post
There seems to be quite a bit of misinformation in your post. I can't find any evidence other than hearsay that the glue in exterior plywood is the same as the highest quality phenolic glues used in marine plywood.

But I have found citations that using PINE plywood is bad news for boat building. Apparently it doesn't take resin well and lacks stiffness among other down sides. One writer said it would be great for building a bench around your fire pit, but not for boat building.

That's what I like about this forum, you get lots of opinions which stimulates discussion and then you have to read for yourself and make up your own mind.
I found this in the very first result of the simple google query <exterior plywood glue>. Marine Plywood Glues

"Both marine and exterior plywood are regulated so that the adhesives used in their manufacture can withstand severe conditions including boiling for several hours.

The main differrence is in the quality of the plies used. Number of knots, joins, repairs, voids are all strictly regulated in marine ply and less so in outside ply."


To complicate this more, there are several grades and qualities of marine plywood, as there are exterior.

All subsequent google links in that query also say pretty much the same thing - many of those sources boat building ones.

So I don't see any misinformation in the post you site, nor any correction of any perceived misinformation in your post.

Again, unless I am missing something about the OP's intended use, many here are way over-thinking this. He isn't coring a deck or building a light hull. He is just looking for a sandwich filler to provide the correct thickness for his port flange and allow screws to bite. He plans on replacing these ports in the near future with ones that mount differently and won't even need the screws. He has also stopped any leaking.

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Old 16-09-2015, 08:29   #42
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Re: Lightweight but strong backing material

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Originally Posted by colemj View Post
I found this in the very first result of the simple google query <exterior plywood glue>. Marine Plywood Glues

"Both marine and exterior plywood are regulated so that the adhesives used in their manufacture can withstand severe conditions including boiling for several hours.

The main differrence is in the quality of the plies used. Number of knots, joins, repairs, voids are all strictly regulated in marine ply and less so in outside ply."


To complicate this more, there are several grades and qualities of marine plywood, as there are exterior.

All subsequent google links in that query also say pretty much the same thing - many of those sources boat building ones.

So I don't see any misinformation in the post you site, nor any correction of any perceived misinformation in your post.

Again, unless I am missing something about the OP's intended use, many here are way over-thinking this. He isn't coring a deck or building a light hull. He is just looking for a sandwich filler to provide the correct thickness for his port flange and allow screws to bite. He plans on replacing these ports in the near future with ones that mount differently and won't even need the screws. He has also stopped any leaking.

Mark
I guess you missed the part about the PINE, and I did find quotations for eg from an importer of plywood both marine and exterior that the glue was DIFFERENT. I do in fact know how to use Google and looked at a variety of sources.

In any case, the OP is best served for his fine Cabo Rico vessel to splurge and buy marine plywood as he does not buy truckloads of plywood, is not a boat builder, does not possess x-ray vision to see voids, doesn't have the "eye" to tell pretty but potentially crappy plywood from good stuff and so on. Further, when I write I assume that the thread will be viewed in the future by someone with a similar problem but an even smaller fund of knowledge than the paltry knowledge I have and try to pass on information that I have obtained. I try to stick to facts, or note that something is only my opinion.

Most of the time I am reluctant to post here at all because in many instances when you take the time to try to help someone everyone wants to argue and it is rare that anyone actually produces facts to back up their opinions.

For myself, I'm not going to buy pine exterior plywood and use it in a boat. Someone might argue buying stuff that "looks pretty" instead of being demonstrably strong is a questionable philosophy. Or trying to save a few cents by buying exterior plywood instead of marine plywood for marine applications, even though I am one of those sailors that can turn a penny into copper wire.

Further, this topic cannot be "overthought." At present, there isn't a great inexpensive alternative to traditional marine plywood for use as core material in boat building. And plywood is far from perfect.
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Old 16-09-2015, 08:42   #43
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Re: Lightweight but strong backing material

There are many other woods used in plywood besides pine. The poster you responded to said that he was using pine ply in a project, but he also seemed to fully understand the specific application he was applying it to.

Different does not equal bad. As every reference states, the glues used in both types of plywoods is highly regulated and have to pass the same performance specs. If both pass the same performance specs, then the specific formulation of glue is neither here nor there. Sort of like choosing between Sikaflex or Lifecaulk for a polysulfide caulk formulation.

And different does not equal good. There are as many glue formulas within marine ply alone as there are between marine and exterior ply. Grouping all marine ply into one pile and all exterior into another is grossly over-simplifying the field.

Again, the OP's need here is not very technically onerous and all the teeth gnashing around technical qualities of different plys, fiberglass, foam, etc is probably over-think.

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Old 16-09-2015, 08:43   #44
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Re: Lightweight but strong backing material

The guy here in Jax and also in STA both have the same marine plywood... AB.

How is this AB different than the exterior AB I buy from home depot?

Is the glue that difference between the two as important (?) given that the wood should "never" or extremely rarely be exposed to water - assuming my sealing work well?

BTW - got a quote for my New Found Ports... 3K+ and up to 4K+ if I move up a size of two. Ouch.
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Old 16-09-2015, 18:18   #45
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Re: Lightweight but strong backing material

AB is not marine grade. AB is defined as good plies (meaning no knots) on the outermost plies. The inner plies are allowed to have knots. And AB allows voids on the inner plies, meaning gaps between the plies.

AA is marine grade. It is the same specification as AB except that no voids are allowed on the inner plies.

AAA is aircraft grade. On AAA there are no voids, and all plies are knot free.
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