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Old 11-05-2013, 10:29   #16
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Re: 3/4 BALSA CORE = X/X PLYWOOD

My balsa cored decks are only 44 years old with no delamination or rot. Will I have to wait another 44 years to see the inevitable doom of the Balsa. The secret to any cored deck is not letting water into the core. Stanchions are the worst violators as the constant torquing of a long lever arm makes keeping a seal very difficult. Anyone who owns a boat should pull their life lines, core the fastener pukas with thickened epoxy, redrill and reinstall. Fortunately, Pearson molded my boat so the stanchions are all in solid uncored fiberglass. If there are SPOTS with sillycone sealant, remove the offending pieces and do your best to remove all traces of the spawn of the devil.

Any organic material soaked in water will rot eventually. On boats there are usually point sources of water intrusion like improperly bedded fasteners. Works to the advantage of Balsa and the disadvantage of Plywood. Balsa core is not manufactured as end grain because of its resistance to rot but for strength and mold-ability. The resistance to widespread rotting is a serendipitous benefit.
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Old 11-05-2013, 10:40   #17
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Re: 3/4 BALSA CORE = X/X PLYWOOD

Yep, nothing wrong with core really, just penetrating it that is the problem. Most boats I've seen the stancions are out far enough near the deck/hull joint that there is no core, unfortunately some of teh inside stancion bolts go thru the very edge of the core though on some.
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Old 11-05-2013, 11:12   #18
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Re: 3/4 BALSA CORE = X/X PLYWOOD

Remember that Kon-Tiki is being released again, their raft was balsa and yes, it saturated enough to be sinking at the end.

Balsa sheets for core will not be available at any local or simple lumber yard, they are a specialty marine lumber product. Most of us would have to have them shipped in and the only good news is that IT IS BALSA so the shipping won't be anywhere near as expensive as it would be for plywood.<G>

Any good coring material, whether it is balsa sheet (end grain assemblies) or Bruneel ply (denser than regular marine ply, used for deck coring) is going to cost money. I would guess that if you can't afford to do it right, one of the hard styrofoam insulation boards comes closest to balsa and that could easily be milled down to an exact thickness, if you could obtain it in a similar density to make it suitable.

All of this is part of why a boat with substantial deck problems costs a bloody fortune to have professionally repaired. If there was a cheap fix that stood up, it would be common by now.
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Old 11-05-2013, 12:24   #19
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Re: 3/4 BALSA CORE = X/X PLYWOOD

I am waiting for the pics to comment...how much area is being replaced?
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Old 11-05-2013, 14:58   #20
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Re: 3/4 BALSA CORE = X/X PLYWOOD

I would go for balsa, it is lighter and easier to form.

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Old 12-05-2013, 10:26   #21
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Re: 3/4 BALSA CORE = X/X PLYWOOD

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Originally Posted by hellosailor View Post
Remember that Kon-Tiki is being released again, their raft was balsa and yes, it saturated enough to be sinking at the end.

Balsa sheets for core will not be available at any local or simple lumber yard, they are a specialty marine lumber product. Most of us would have to have them shipped in and the only good news is that IT IS BALSA so the shipping won't be anywhere near as expensive as it would be for plywood.<G>

Any good coring material, whether it is balsa sheet (end grain assemblies) or Bruneel ply (denser than regular marine ply, used for deck coring) is going to cost money. I would guess that if you can't afford to do it right, one of the hard styrofoam insulation boards comes closest to balsa and that could easily be milled down to an exact thickness, if you could obtain it in a similar density to make it suitable.

All of this is part of why a boat with substantial deck problems costs a bloody fortune to have professionally repaired. If there was a cheap fix that stood up, it would be common by now.
Styrofoam melts when laminating resin is applied!
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Old 12-05-2013, 10:54   #22
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Re: 3/4 BALSA CORE = X/X PLYWOOD

IIRC it melts with polyester resin, but epoxy resin won't bother it.
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Old 12-05-2013, 10:59   #23
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Re: 3/4 BALSA CORE = X/X PLYWOOD

If he's trying to save money using styrofoam... he wont be using epoxy! Thinking more about styrofoam.... it has little compressive strength compared with balsa... probably a bad idea anyway... these jobs are too much work to put the wrong stuff in there. To save money just cut cheap exterior plywood into squares (Passport used 3" squares with resin in between each square to avoid water migration.).
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Old 12-05-2013, 16:06   #24
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Re: 3/4 BALSA CORE = X/X PLYWOOD

If you are going plywood, any exterior plywood will do just fine though I'd probably go up to AB grade to get better face sheets. Save the brunzeel or marine ply for Bulkheads and furniture.
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Old 13-05-2013, 10:13   #25
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Re: 3/4 Balsa Core = X/X Plywood

Yep, exterior uses the same glue as marine ply. The only real difference is the quality of the wood as far as number of voids in the ply. In a sandwich deck... who cares if there's a void here and there!
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Old 13-05-2013, 11:30   #26
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Re: 3/4 Balsa Core = X/X Plywood

Quote:
Originally Posted by Cheechako View Post
Yep, exterior uses the same glue as marine ply. The only real difference is the quality of the wood as far as number of voids in the ply. In a sandwich deck... who cares if there's a void here and there!

Number of plies is the big difference.
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Old 13-05-2013, 11:49   #27
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Re: 3/4 Balsa Core = X/X Plywood

Good point, does plain old Fir marine ply have more layers too? or just the high end stuff like Bruynzeel? Come to think of it.... if the OP is going to use ply...,. why not buy Cedar fencing material instead...I think it comes about 5 or 6 ft long and 4-5 " wide. Cut that into squares! it's got a rough milled surface perfect for adhesion, it's light and cedar will last about 40 years or more, and loves water!
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Old 13-05-2013, 17:13   #28
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Re: 3/4 Balsa Core = X/X Plywood

Squares are bunk. I've done ply up to 1" in single layer with no problems bending. In the few cases where there's too much shape you kerf the back side on a table saw first. This gives a nice fair surface to glass too. If you try to do squares it'll be a nightmare. What works in a mold does not in a repair.
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Old 13-05-2013, 17:58   #29
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Re: 3/4 Balsa Core = X/X Plywood

My first choice would be end-grain balsa. Second some other nice light and easily worked wood like spruce or douglas fir cut in the same end grain way. Distant third would be plywood of any kind as it will not be end-grain cut. Last would be foam as the laminate engineering is quite different for foam as it is much more crushable.

Wood blocks are so easy to cut, and conform to curves, and can be epoxy dipped to prevent water migration. The choice seems obvious.
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Old 13-05-2013, 18:00   #30
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Re: 3/4 Balsa Core = X/X Plywood

I think the point of squares in Passport's case was that they left room between each square ..3/16-1/4" and filled with resin slurry to avoid water migration. But yeah , right, just table saw slots and you can use much bigger pieces.... and they ought to help resin "grip" the wood too... let's face it... it's the "beam" crated by the two separated layers of glass that give the stiffness, the core is just filler and something to "grip" to keep the glass layers for flexing independently...
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