How to know plywood grade?

[GregE]

I've had my aluminum jon boat for about a year now. The guy before me had a deck put down (floor as some say) in the bottom on the stringers (ribs) and it's covered with a carpet. Installed about 18 months ago I guess. I'm going to eventually take it out to do some work, but how do I know whether this is marine grade plywood or not? He said that his installer told him it was, but I think terminology, when talking grades of plywood, gets thrown around incorrectly sometimes.

So, when I unscrew it and flip it over, is there a way to know what grade of wood it is? If it's regular exterior pressure treated, it's most definitely getting pulled out of there since it's resting on all of the aluminum stringers.

 

[tashasdaddy]

Re: How to know plywood grade?

it is probably exterior grade and was not sealed. covered with carpet, so it stayed wet, what do you expect. properly sealed, it would last 10-20 years.

 

[salty87]

Re: How to know plywood grade?

just me but i'd assume that most people wouldn't use marine grade in a jon boat. you have to search for it a bit and it isn't cheap. who has an installer for a jon boat?

i just bought some and the only real way to tell by looking is a stamp on the edge, probably gone on yours by now. i'm no expert though.

 

[GregE]

Re: How to know plywood grade?

...who has an installer for a jon boat?

...only real way to tell by looking is a stamp on the edge...

Well, by "installer" I just meant the guy that put it in for him and carpeted it. It's about a 4ft x 7ft piece, with cutouts for side ribs, and is carpeted. I'll unscrew it and flip it over, and also take the carpet off. If there was ever a stamp on the underside, it will still be there. If it is on the carpeted side, will be harder to decipher, if it can be at all. This wood hasn't gotten wet to any significant degree.

 

[redfury]

Re: How to know plywood grade?

I was under the assumption that marine grade plywood was plywood that consisted of more layers of better grade wood than standard plywood you'd buy at Home Depot.
This is what I found with a quick search.

BS 1088 Plywood

The following are brief excerpts from the full BS 1088 specification, and this material is for your general information only.

BS 1088 Specification -- This standard applies to plywood produced with untreated tropical hardwood veneers that have a set level of resistance to fungal attack. The plies are bonded with WBP glue. The finished product doesn't have to be "British made".

WBP Glue Line -- BS 1088 plywood must use an adhesive proven to be very resistant to weather, micro-organisms, cold and boiling water, and steam and dry heat. The product's bonding must pass a series of British Standard tests.

Face Veneers -- These must present a solid surface that is free from open defects. Face veneers must be free of knots other than "sound pin" knots, and there can be no more than an average of two such knots per square foot over the entire surface of the plywood sheet. The veneers must be reasonably free from irregular grain. The use of edge joints is limited, and end joints are not allowed.

Core Veneers -- Core veneers have the same basic requirements as face veneers, except that small splits are allowed, and there is no limit on the number of pin knots or edge joints. However, end joints are not permitted.

Limits of Manufacturing Defects -- Defective bonds, pleats and overlaps, and gaps in faces are not permitted. Occasional gaps may be repaired using veneer inserts bonded with the proper adhesive.

Moisture Content -- BS 1088 plywood must have a moisture content between 6% and 14% when it leaves the factory.

 

[JustJason]

Re: How to know plywood grade?

you can use pine if you know how to fiberglass

 

[Chris1956]

Re: How to know plywood grade?

Greg, That plywood of yours is of one of two grades. It is either rotted or not rotted. Not much else matters at this time. If it is rotted, tear it out and replace it with a piece of dry, pressure treated plywood that has two coats of polyester resin on all it's sides.

if the plywood is not rotted, and you can dry it out, you can seal it with resin. Or you can ignore it until it rots out. All plywood will rot, if left unprotected. The time to rot is not too much different between marine and non-marine plywood. Since marine plywood is voidless, it just take longer to get weak from rot.

My .02

 

[woodee148]

Re: How to know plywood grade?

my .01
I would check into how the pressure treat will affect the aluminum. As far as I know the new(er) ACQ (as well as the old CCA) pressure treated is extremely corrosive to aluminum and should not come into direct contact with it. I realize Chris had suggested to put two coats on but I would still not recommend using it. Second if you are going to seal it i would not spend the extra on pressure treat. I am not familiar with this application but i am involved in the pressure treated industry.
I think like other posters have said, if it ain't broke fix it

Woody