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Author Topic:   Marine Plywood vs. Exterior Plywood
bradenton_whaler posted 03-06-2003 11:14 PM ET (US)   Profile for bradenton_whaler   Send Email to bradenton_whaler  
What is the difference? I am planning on replacing the floor board of my console and will seal the board water tight, does it matter if I choose to go with marine ply or exterior ply? It likely has something to do with the glue used to create the plywood?


captbone posted 03-07-2003 12:01 AM ET (US)     Profile for captbone  Send Email to captbone     
I would use the marine ply. If you ever sell it, it will be an asset, I sure as heck would ask how the repair was done and with what. In theory you could do it will partical board and bondo but you want the repair to last a life time. Just my 2 cents
John O posted 03-07-2003 12:18 AM ET (US)     Profile for John O    
I was under the impression that marine grade plywood had no voids in the laminations.
Tom W Clark posted 03-07-2003 01:41 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Marine plywood and exterior grade plywood both use the same glue. The difference between the two is that marine plywood is supposed to void free, just as John O points out.

In reality, marine grade is generally just nicer but it depends on the grade. Same is true of exterior grade. You definitely do not want to use anything as nasty as CDX. ACX would be an absolute minimum grade of exterior plywood. ABX would be better.

As in all things, inspect the plywood with your eyes. Don't just rely on some label or something a salesman tells you. Count the number of plys. Is the face veneer good? Try bending it. These tests will tell you a lot about the sheet of plywood in question.

Having said all that I would go on to say that yes, exterior plywood will probaby be just fine for this application.

Shadow posted 03-07-2003 07:50 AM ET (US)     Profile for Shadow  Send Email to Shadow     
I was told marine 3/4 marine plywood has thinner sheets but has 2 extra sheets, also no voids and has water proof glue. It certainly looks better. If it is stained I would use marine plywood, if you are useing it in a transom or floor I'd use pressure treated plywood.
Kevin D posted 03-07-2003 07:57 AM ET (US)     Profile for Kevin D  Send Email to Kevin D     
I'd like to replace the wood in my 15sport. I've seen some nice red oak ply at Home Depot, what is your opinion on using this type of wood.
JBCornwell posted 03-07-2003 08:09 AM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Hello, Kevin.

In a 15 Sport, I would only use solid "mahogany", even for the locker cover.

Red sky at night. . .

bradenton_whaler posted 03-07-2003 09:27 AM ET (US)     Profile for bradenton_whaler  Send Email to bradenton_whaler     
Thanks for all the input! I'm just doing the cost-benefit analysis. Home Depot requires you to purchase an entire sheet ($52) of marine plywood where I can buy a half sheet of exterior plywood for ($7).
Whaler Proud posted 03-07-2003 09:59 AM ET (US)     Profile for Whaler Proud  Send Email to Whaler Proud     

I agree with JB on the oak. Look at this thread for some reasons why you want to avoid it. Also, the cost of red oak vs. mahogany really isn't all that much if you shop around. Especially if you factor in the maintenance issues with oak.

wayne baker posted 03-07-2003 02:25 PM ET (US)     Profile for wayne baker  Send Email to wayne baker     
Is mahogany plywood mahogany all the way through or is the mahogany just a venere on top?
lhg posted 03-07-2003 02:38 PM ET (US)     Profile for lhg    
The mahogany marine plywood I used to build my Nauset console & seats (in 1971), had a nice surface veneer, on the top side only, of Philippine Mahogany and luan mahogany, the cheap stuff, as interior veneers and on the bottom surface.

The teak floor sump covers on my Outrage are the same, with only a teak veneer on the top surface, the rest being mahogany.

Teak or Mahogany Marine plywood has more, thinner veneers, with no interior voids (supposedly).

Kevin D posted 03-07-2003 02:55 PM ET (US)     Profile for Kevin D  Send Email to Kevin D     
Whaler Proud, Thanks for the thread on using red oak. I think it best to stick with the mahogany. Thanks Kevin
acassidy posted 03-07-2003 02:58 PM ET (US)     Profile for acassidy  Send Email to acassidy     
If you buy exterior, do not get pine. Exterior grade Douglas Fir AC or BC is about as close as you can get to marine grade without the high cost. Marine grade is usually Douglas Fir AA or AB with more plies than normal and has no void in the inner plies. Same glue and same wood as exterior Douglas fir with about double the price. Stay away from pressure treated unless you are making a deck for your BBQ pit. Pressure treated warps bad, is wet and resin will not stick to it unless you really let it dry and for goodness sake it is pine, which has no place in a Whaler. Fir loves resin, is light and strong and will last a long time. Archie
John O posted 03-07-2003 08:45 PM ET (US)     Profile for John O    
Would fir be the best choice for building a shelf in my Newtauk CC? I would cover it in resin for added durability.
acassidy posted 03-08-2003 07:35 AM ET (US)     Profile for acassidy  Send Email to acassidy     
John O, Fir would be perfect for a shelf in your console. Two years ago I cut out two holes in my console for two batteries, and I am about 99% sure that the wood I cut out was marine grade fir. Epoxy resin is the best for coating wood like you want and it will last a very long time. Archie
John O posted 03-08-2003 07:38 AM ET (US)     Profile for John O    
Thanks--- and so another project begins !
xue9918 posted 09-05-2008 11:05 PM ET (US)     Profile for xue9918  Send Email to xue9918     
Please refer to :
Marine Plywood: A Comparison With General Exterior Plywood
nitro vinny posted 09-06-2008 09:58 AM ET (US)     Profile for nitro vinny  Send Email to nitro vinny     
I just replaced the floor on my Newport 17 with 3/8" pine plywood and sealed it with 2 coats of resin. The old floor was pine plywood which has a green tint. The green tint appears to be an anti-fungal/rot treatment similar to COPPO (coppernapthenate). Back when urea based resin was used in plywood manufacturing it was very important to use marine plywood (where needed) which, in addition to having superior ply count/grade, used phenolic based resin. Virtually all plywood made today uses phenolic based resin. Out of curiosity I did a soak test of plywood scraps laying around the shop; none delaminated.

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