# Marine Plywood & Bulkheads



## Beersmith (Nov 5, 2008)

I am needing to replace many of Windsong's bulkheads and cabinets due to a lot of rot from years of neglected leaks. 

I am having trouble finding a local supplier of marine plywood, and am not too excited about the price of what I have seen out there. I plan on using marine plywood, so don't get on my case too hard...I'd just like to see if the alternatives are suitable for above the waterline, and in theory, dry work. 

So, must I use marine plywood for interior cabinetry and bulkheads? I plan on covering each piece of wood I use with epoxy to seal it up and prevent water intrusion, but I know that isn't 100% effective in the long run. I'd love to be able to save some cash and time by not having to find and use marine grade plywood, but if the argument for using it is compelling I will stick to that route. 

(and before some smart guy says I should worry about the leaks first...yes, I've got that covered  )


----------



## SlowButSteady (Feb 17, 2010)

Supposedly, marine-grade and exterior-grade plywood used the same adhesives. The difference is that marine-grade plywood has no interior voids, while for exterior-grade plywood a certain percentage of "void space" is allowed. I would think that a good exterior-grade plywood, with a couple-three of layers of penetrating epoxy on all surfaces (maybe a layer or two extra along the edges) would be as strong and rot-resistant as you can get. Slap a nice-looking treatment (wood "door skin", Formica, or whatever) on the exposed surfaces and it would look like a million bucks.

The "You're-full-of-crap" posts may commence ...... _now_.


----------



## LandLocked66c (Dec 5, 2009)

I replaced my sole with standard plywood, sealed and potted of course. 

Marine grade also has more/thinner ply which allows it to be stronger and lighter. Some say it will also rot slower because of having more ply. Boats were built before marine grade was around so I care not what others say about using/not using it. If it stays dry it should be more than adequate for a bulkhead.


----------



## tommays (Sep 9, 2008)

I think your will find the marine plywood more stable due the larger amount of plys which is how they also make furniture grade ply before applying the veneer 

I find SOME exterior-grade plywood is unhappy and try's to imitate a potato chip shape unless its nailed to house


----------



## Siamese (May 9, 2007)

If regular plywood's okay, why not just use OSB?


----------



## LandLocked66c (Dec 5, 2009)

Siamese said:


> If regular plywood's okay, why not just use OSB?


I believe Chrysler boats did, didn't they? 

Or was that press board?

I can tell you that my 1970 Oday does not have marine grade plywood at all! Nor did it ever.


----------



## JohnRPollard (Mar 26, 2007)

Hi Beeresmith,

I would really encourage you to stick with marine ply. Bulkheads are structural. BS 1088 marine ply will stand-up better, due to better laminate schedule and minimal voids.

I have several sources of marine ply from whom I purchase. If you do not need a teak veneer, you can get Sapele or Okoume from Chesapeake Light Craft. While not local to you, they are top notch, very good to work with and are experienced at shipping anywhere.

If you would like to get a teak veneer -- which usually looks very nice on boats -- you can order sheets from Buck Woodcraft right there in Marathon FL. I've been very happy with the teak veneers I've received from them -- which I've used for cabinetry.

Yes, it's expensive compared to regular ply. But the real cost of most jobs is the time and effort. It rarely makes good sense to skimp on the supplies.


----------



## AirborneSF (Dec 14, 2010)

PT boats were built from marine plywood, must be good for something? .02


----------



## mitiempo (Sep 19, 2008)

If it is for cabinets and not bulkheads exterior ply is ok. It would depend on the finish you want. Most exterior grade ply is fir and if you are going to paint it is very hard to get a good finish on fir. But if you are going to use a laminate no problem. For bulkheads marine ply is worth the extra. More plies, more stable, will take a paint finish well if not fir. Marine ply is not lighter though.


----------



## ccriders (Jul 8, 2006)

Exterior plywood is never going to look good unless covered with formica or some other such product. So factor that cost and time into the cost calculation. Most exterior plywood is of atrocious quality, the outer skins so rough and porous you would have to sand half of it away to get a level of smoothness for any kind of finish material. And with patches and voids all over the sheet you can never be confident that the area around the chainplate bolts is good solid material. Finally, most of it never lays flat and will drive you crazy.
There are reasons it is so cheap.
John


----------



## ambianceack (Aug 27, 2006)

We have a couple of boats and I am slowly restoring a catalina 22. The PO used AC grade plywood good on one side for some of the covers to storage areas. I painted them with a gray latex paint and they have held up just fine. The covers are in the interior of the boat for the six years we have owned the catalina. She is not the prettiest girl at the dance but a lot of fun to sail even with the exterior plywood storage covers.


----------



## mitiempo (Sep 19, 2008)

Exterior ply and marine ply both use waterproof glues. But the strength, stability, and ability to take a finish (if the marine ply is not fir) are vastly different.


----------



## LandLocked66c (Dec 5, 2009)

*Exterior Plywood*

Exterior is the grade given to any plywood which is bonded with 100 percent waterproof adhesive and is intended for permanent outdoor exposure. Exterior plywood must be graded a C or above, meaning knots and knot holes of up to 1½ inches are allowed. The species of wood can also vary and often different species are combined. Core gap size for Exterior wood cannot exceed 1 inch wide. Exterior wood is good for most all wood needs, and can be purchased to look almost identical to Marine plywood at a much lower cost.

Plywood graded C-D or CDX is often mistaken for exterior plywood, but is not approved by the APA for outdoor exposure. CDX plywood is considered Exposure 1 plywood where it can encounter high moisture content, but needs to be sealed for complete outdoor use.

*Marine Plywood*

Made entirely of Douglas Fir or Western Larch, marine grade is one of the highest designations which can be given to a piece of plywood and is considered to be "premium." In order to be marine grade plywood, the outer plies must be graded at least a B or better. B grading means that the wood may have some knots, but no knot holes. In order to be A grade ply, there cannot be any knots or knotholes present in the layer. The maximum core gap size allowed is an 1/8 of an inch, and both outer panels must be sanded, Medium Density Overlay or High Density Overlay. The durability rating must be Exterior and fully waterproof structural adhesive is used.

Read more: http://www.doityourself.com/stry/marine-plywood-vs-exterior-plywood#ixzz1I2B6FoGZ


----------



## mitiempo (Sep 19, 2008)

The best marine ply is BS1088 certified. It is usually occume. The 2 more popular makes are Joubert in France (occume which is African Mahogany) and Hydro-Tek (Meranti which is a mahogany) made in Malaysia. Both are BS1088.
Aqua-Tek is made in Malaysia and is BS 6566 certified. 
3/4" Joubert is 9 ply, 3/4" Hydro-Tek is 13 ply and 3/4' Aqua-Tek is 11 ply. 
The Joubert ply has no voids allowed in any ply, patched or otherwise. Easy to work with, very stable and strong, and takes any finish you like.

Domestic ply in the better grades has deteriorated in quality over the years. When I was young you had trouble telling which side was the bad side of good one side ply. Now you have trouble telling which is the good side.


----------



## Beersmith (Nov 5, 2008)

Thanks so much for all of the re*plies* (heh) everyone. I think I will go for the marine ply. With the amount of time and effort I am putting into this project, it would be silly to skimp on something as important as the bulkheads. The fact that I am replacing them because they rotted away also leads me to want the more rot-resistant choice. Once the job is done, I think I will be happy I spent a bit more for the higher quality wood. This is the same philosophy I am going with for deck painting by using Perfection instead of Brightsides. I am going through countless hours in preparation, I might as well do it right.


----------



## LandLocked66c (Dec 5, 2009)

With a boat like yours, I'd say that's the way to go! With a cheapy like mine, wouldn't be worth it!


----------



## kjzerr (Aug 19, 2012)

I have done some research regarding the use of marine grade plywood vs. exterior grade for interior boat work. It seems to me that exterior grade is acceptable from a longevity perspective. Granted that it usually is not pretty, but I plan to skin all of mine with a veneer (type of wood TBD), so the "look" of the plywood is not really important in my case.


----------



## zeehag (Nov 16, 2008)

we used regular plywood but inspected it well for flaws and then thoroughly penetrated it with epoxy and wrapped it with fg cloth and resin. is my structural bulkhead forward. has been in place 2 yrs and is solid. same with deck backing plate we replaced due to excessive wet rot.....is awesome.


----------



## SloopJonB (Jun 6, 2011)

LandLocked66c said:


> *Exterior Plywood*
> 
> Exterior is the grade given to any plywood which is bonded with 100 percent waterproof adhesive and is intended for permanent outdoor exposure. Exterior plywood must be graded a C or above, meaning knots and knot holes of up to 1½ inches are allowed. The species of wood can also vary and often different species are combined. Core gap size for Exterior wood cannot exceed 1 inch wide. Exterior wood is good for most all wood needs, and can be purchased to look almost identical to Marine plywood at a much lower cost.
> 
> ...


Good advice. True marine ply is hugely expensive - up to 10X the cost of good exterior ply. If you are building a dinghy hull or something it is worth spending the extra money but for interior rough construction on a "big" boat it is not worth the price unless your budget is unlimited.

I have never been on a production boat that used it AFAIK.

I have always used good exterior ply and sealed the edges with epoxy - never a hint of a problem.


----------



## Beersmith (Nov 5, 2008)

just an update to this since it got bumped

I've been using some high quality Fir plywood, though not marine grade, for the bulkheads and such. However, I did coat each cut piece with 3 layers of epoxy (6 layers on the edges) before mounting. I figure the epoxy treatment would make them as impervious as possible.


----------



## Panscher (Dec 22, 2015)

Hello,

I am looking for a high quality laminate (that can be glued to marine grade plywood ) with imitation wood design (preferably a light colour such as birch) for use on motor boat bulkheads. Where in the USA can I purchase this material. 

Thanks ,

Panscher


----------



## mitiempo (Sep 19, 2008)

Panscher said:


> Hello,
> 
> I am looking for a high quality laminate (that can be glued to marine grade plywood ) with imitation wood design (preferably a light colour such as birch) for use on motor boat bulkheads. Where in the USA can I purchase this material.
> 
> ...


Google Arborite or Wilson Art laminate. Available at many building supply stores.


----------



## SloopJonB (Jun 6, 2011)

Beersmith said:


> just an update to this since it got bumped
> 
> I've been using some high quality Fir plywood, though not marine grade, for the bulkheads and such. However, I did coat each cut piece with 3 layers of epoxy (6 layers on the edges) before mounting. I figure the epoxy treatment would make them as impervious as possible.


FYI, this was the mahogany marine ply cabin sole of my boat.

I've never seen exterior fir delaminate like that in any circumstance.


----------



## SloopJonB (Jun 6, 2011)

Panscher said:


> Hello,
> 
> I am looking for a high quality laminate (that can be glued to marine grade plywood ) with imitation wood design (preferably a light colour such as birch) for use on motor boat bulkheads. Where in the USA can I purchase this material.
> 
> ...


Don't do it! If you want laminate, use something that looks like laminate - it can be extremely attractive.

Fake wood laminate *always* looks cheap & phony - it was one of the principal reasons for "plastic" becoming a pejorative decades ago.


----------



## mitiempo (Sep 19, 2008)

SloopJonB said:


> Don't do it! If you want laminate, use something that looks like laminate - it can be extremely attractive.
> 
> Fake wood laminate *always* looks cheap & phony - it was one of the principal reasons for "plastic" becoming a pejorative decades ago.


I agree with this. Laminate in colors - white or off white - looks good on bulkheads. Fake wood laminate will make the boat look like a 40 year old Pearson!


----------



## roverhi (Dec 19, 2013)

I used birch ply that is made for cabinets. The birch exterior finishes up fine for painting. The glue is exterior grade though probably not as water resistant as true exterior or marine grade. This was for interior furniture, not structural bulkheads. 

You can get marine grade ply in various wood exterior skins. Fir does not finish well for painting and really only be works for exposed surfaces that will be covered with Formica. Have gotten marine grade that was made out of Philippine Mahogany and it was crap. Took multiple coats of primer sanded off to fill the surface smooth and the wood was very soft and rot prone. 

Plywood is graded by the exterior skins, whatever whatever they are. A/C grade has one good side and one pretty good side. Fine for cabinets or other stuff you only need one really good side. A/B is typically what Marine Ply is. B side is pretty damn good but not quite perfect. Exotic material skins like Teak or African Mahogany are usually A/A exterior skins though often aren't marine ply and are very costly. C/D X is the typical construction grade plywood you get at Home Depot. Its got one bad side, the other even worse and usually some pretty good voids though it uses water proof glue and is very resistant to delaminating when soaked.

Bruynzeel is the caviar of plywood types. It is made from relative hardwoods with many thin plys. Finishes off beautifully, ultra strong and EXPENSIVE. Lovely stuff if you can find and afford it.


----------



## mitiempo (Sep 19, 2008)

roverhi said:


> Bruynzeel is the caviar of plywood types. It is made from relative hardwoods with many thin plys. Finishes off beautifully, ultra strong and EXPENSIVE. Lovely stuff if you can find and afford it.


There isn't as far as I know any good quality domestic (North American made) marine plywood. Aqua Tek and Hydro Tek are very high quality imported marine plywoods. Joubert, for example does not allow any voids, even patched, in any ply on some of their products. 12 mm (1/2") is 7 ply and 18 mm (3/4") is 13 ply. Not cheap but a joy to work with. Same BS1088 standard as Bruynzeel.

Marine Grade Plywood | West Wind Hardwood


----------



## Brent Swain (Jan 16, 2012)

Used plywood which has been exposed to weather for a long time without delaminating is as safe as it gets. You can put whatever veneer or or covering you want over it.


----------



## mitiempo (Sep 19, 2008)

Brent Swain said:


> Used plywood which has been exposed to weather for a long time without delaminating is as safe as it gets. You can put whatever veneer or or covering you want over it.


But Brent, not everybody wants to dumpster dive like you.:laugh


----------

