what makes marine plywood

[A.V.]

I just bought a sheet of marine plywood (115.00 Can.) and I was surprized to see voids in the plys on the edges, it's not marked in any way "marine" THANKS

[Carpenter]

Some plywood panels are designed for special uses, including marine decorative underlayment and concrete form and special exterior applications. The treating of plywood with preservatives and fire retardants is done by people outside of the plywood industry. Consequently, there are no formal grades of treated plywood. Plywood is easily pressure-treated with waterborne preservatives and fire retardants, and treated plywood is readily available for use where such protection is needed.

[scooter]

I manage a small lumber yard here in Milw.and all of the marine grade plywood I ever saw was edge treated and sealed.The one bad part about marine ply is that when you cut you have to seal it again.When someone asks for a sheet of ply to fix a floor or pontoon deck.I give them a few choices and prices.They can buy the marine grade or I always recomend a high quality A.C. grade exterior glue.Or a high quality Underlayment grade ply again with exterior glue.
The main reason for this, is both plywoods are for the most part void free near the top layers of the ven.Also they are consideralby less costly.And you will have to seal the sheet if you cut it any way.Most use a high quality primer/sealer and or a product like Thompsons water sealer.
I have also seen people completly fiberglass encase the ply after they have cut it to size.This is still alot cheaper than marine grade ply.In my area marine grade ply sells for about $ 85.00 compared to A.C. grade that runs about $32.00 U.L.grade is about the same.So for about $ 10.00 more in products you will problably need anyway you get virtually the same application.
If I was to build a boat out of ply itself I wouldnt hesitate to use the marine grade ply.If I was just fixen a floor I would go the other way.


I hope this helps
Scooter

[Boatnut]

A.V.,
seems the term "marine plywood" covers a lot of things. If you intend to use fir, then I've always been told not to waste my money and just use a good A/C exterior plywood. Depends on what type of wood you want the veneers made out of. The following is from a website:

"The glue is often mistakenly considered to be superior to WBP, in fact the same glue is used. The principal difference between Marine Grade and Exterior plywood is as follows :

1) The quality and grading requirements of the veneers (especially face veneers) are more stringent.

2) Higher standards of workmanship in the laying-up and manufacture of the plywood are necessary.

3) Core gaps are restricted to one per board, not wider than 0.5mm.

4) Each sheet must be marked on the back or edge with the manufacturers name, country of origin and "BS 1088 WBP".

5) Each board is made in accordance to British Standard 1088, the standard the Marine Grade Plywood.

Here are a few links, you can judge for yourself.

http://ourworld.compuserve.com/homepages/wood_international_agency/marinegr.htm

http://www.worldpanel.com/Marineplywoods.htm

http://www.gatorboats.com/Frequently-Asked-Questions.htm

[marcbodi]

Hi,
The difference in Plywood and in Marine from what I was told is in the glue and chemicals to make it water resistance.Marine Plywood is not Fire resistance it burns like #####.

[targa2]

Iv'e said it before and I'll say it again.Good one side fir plywood is the best and it is only $50 bucks a sheet Canadian. Ive seen peices of this stuff around my farm that have sat unprotected in the elements for 5 years that still retain their structural integrity. Take it from a carpenter.