Marine Grade Plywood Debate Thread...

[Woodonglass]

Re: Marine Grade Plywood Debate Thread...

I have done a LOT of reading on MDO and HDO and it has been used in boat building since the 50's. Both above and below the waterline. Chris Craft and Owens used in in some of their boats. In all fairness it has mixed reviews with some loving it and some not. If you want to learn more just Google HDO and MDO in Marine Use and you'll find plenty of reading material. I will continue to consider it as an optimal product to use for boat restoration until someone can definitively show reasons why not to. Again, for Me, the pros, outweigh the Cons. But, that's just me.... to each his own. Epoxy adheres to it very well and as long as you use a layer of mat between laminations using poly you should have no issues with adhesion. You should shear wood before the outer resin facing fails.

Oh, I guess you all can tell, I really like this stuff!!!

 

[Cadwelder]

Re: Marine Grade Plywood Debate Thread...

I have done a LOT of reading on MDO and HDO and it has been used in boat building since the 50's. Both above and below the waterline. Chris Craft and Owens used in in some of their boats. In all fairness it has mixed reviews with some loving it and some not. If you want to learn more just Google HDO and MDO in Marine Use and you'll find plenty of reading material. I will continue to consider it as an optimal product to use for boat restoration until someone can definitively show reasons why not to. Again, for Me, the pros, outweigh the Cons. But, that's just me.... to each his own. Epoxy adheres to it very well and as long as you use a layer of mat between laminations using poly you should have no issues with adhesion. You should shear wood before the outer resin facing fails.

Oh, I guess you all can tell, I really like this stuff!!!

Well as most my know here I'm a BIG pusher of MG, but because of this thread I've done some extensive reading about the MDO and dang if it's not really convincing (sorry YD). I looked up the weight and Wood is correct about that too....actually a little lighter than MG...but close enough for me not to be an issue for me.

The MDO was designed for exterior signage....now that's some water resistant designing to me and also carries a good solid core (another quaility needed for signage, you don't want it to warp all up). I will alway stay with the quailty material for boats, but I'm going to read some more about this MDO as it seems to be falling in line with "quaility materials"

 

[rickryder]

Re: Marine Grade Plywood Debate Thread...

I'm a little suspicious about the MDO/HDO... They state that they resist moisture penetration and deterioration from many chemicals and solvents..... I would think resin falls in the category of a chemical and if the HDO wont absorb it how will it bond?

 

[Yacht Dr.]

Re: Marine Grade Plywood Debate Thread...

I have used MDO before ( making a custom sign ). It does seem like a viable alternative in boat repairs.

However since I have never used in a marine environment its hard suggest one way or another.

After Extensive research on MDO I have my reserves about glassing on/over the paper overlay.

If I had to bet my life on using properly glassed MDO vs. any non-properly prepped/glassed ply ( including MG ) I would have to choose MDO.

As with anything .. Prep IS KEY. .. that and air void free glass lams .

YD.

 

[Yacht Dr.]

Re: Marine Grade Plywood Debate Thread...

After further review...

MG vs MDO .. MG had void free lams and MDO/HDO does NOT !

After talking with suppliers and manufacures of MDO.. .. MDO is not rated for marine "structural" enviroment...

Neither is HDO ..

From what I gather the inner ply of HDO or MDO is "C" grade. Nobody could recommend HDO or MDO vs. MG on the phone...

And nobody could answer questions about bonding capabilities with poly to there outer skin....

All I got is " this was made for signs " .

Peace out .. YD...

 

[Cadwelder]

Re: Marine Grade Plywood Debate Thread...

You get a better review from sales people than from manufactuers information. I'm still gonna give it a shot and experment around it.

 

[whydididothis1]

Re: Marine Grade Plywood Debate Thread...

what about advantech looks like some good stuff to me,

 

[Cadwelder]

Re: Marine Grade Plywood Debate Thread...

what about advantech looks like some good stuff to me,

Nope checked that one out a while back.....I even emailed AdvanTech and they responded with "Our product is not recommend for any marine use". It's a residential building product.

 

[ondarvr]

Re: Marine Grade Plywood Debate Thread...

It sounds as if Marine grade ply is being discussed as one product when it actually comes in many types,
styles and different woods, each selected for specific characteristics needed in the construction of a specific watercraft. The other problem is suppliers can call almost anything marine ply within reason, so don't think you're buying an actual Lloyds certified product from the local lumber yard for $65.00

Marine ply can have voids, no voids, poor veneers, excellent veneers, great glue, not so good glue, not be that rot resistant, be very rot resistant, it can be heavy, light, flexible, brittle etc.

It all depends on what you want to do with it, for wooden boats you figure out the boat design, how the boat will be used, how it will be constructed and then start trying to pick a specific plywood to use that best meets the needs.

 

[Woodonglass]

Re: Marine Grade Plywood Debate Thread...

Now that ^^^^^ is ONE intelligent statement. Every boat builder should take their specific needs under consideration when deciding on what materials to use.

 

[Woodonglass]

Re: Marine Grade Plywood Debate Thread...

After further review...

MG vs MDO .. MG had void free lams and MDO/HDO does NOT !

After talking with suppliers and manufacures of MDO.. .. MDO is not rated for marine "structural" enviroment...

Neither is HDO ..

From what I gather the inner ply of HDO or MDO is "C" grade. Nobody could recommend HDO or MDO vs. MG on the phone...

And nobody could answer questions about bonding capabilities with poly to there outer skin....

All I got is " this was made for signs " .

Peace out .. YD...

I would be VERY interested in knowing what manufacturer's you spoke with.

Direct quote from the APA

Frequently Asked Questions: Products

What is Marine-grade plywood?

Marine-grade plywood is a specially designed panel made entirely of Douglas-fir or Western Larch. The grade of all plies of veneer is B or better, which means it may have knots, but no knotholes. The panels are sanded on both faces, and are also available with Medium Density Overlay (MDO) or High Density Overlay (HDO) faces. The maximum core-gap size permitted is 1/8 inch. Its exposure durability rating is EXTERIOR and the glue used is a fully waterproof structural adhesive. It is considered a ?premium? panel grade for use in situations where these characteristics are required, i.e., for boat hulls and other marine applications where bending is involved.
Marine-grade plywood is available in 4x8-foot sheets of 1/4, 3/8, 1/2, 5/8 and 3/4-inch thickness. Sheets up to 5x12 feet are also available. Available grades are A-A, A-B, B-B (face-back), MDO and HDO.
Marine-grade plywood is not treated with any chemicals to enhance its resistance to decay. If decay is a concern, it should be pressure-preservative treated to an appropriate standard.
The detailed description of veneer grades and Marine-grade plywood is contained in Voluntary Product Standard PS 1-09: Structural Plywood.
Sample Specification For Marine-Grade:
APA 3/8? B-B Marine Grade 4x8 10 pieces

 

[iSteelHead]

Re: Marine Grade Plywood Debate Thread...

In my opinion. They make "Marine Grade" ply-wood for a specific reason/use. Not to try and rob you of your pocket money. If the manufacturers all used X plywood, then they would certainly have more complaints about rotten transoms, and floors. Warranty claims would start to show up everywhere, and then the company would go under. You see, there is lot more people out there boating, than on this forum. Who disregard what responsible boat owners call "proper maintenance".

The good boaters are out weighed by the bad, in terms of maintenance. Most people use and abuse their boat, and could care less about the soft spots in the floor, until that one day.

The only possible way i could see using other than MG plywood. The wood is treated correctly, boat is rarely used, and is always stored inside. Most boats are stored outdoors, because most people don't have room inside. Most boats also sit outside more than 300 days a year. another great reason to use MG plywood. Just my $.02 - iSteel

 

[ondarvr]

Re: Marine Grade Plywood Debate Thread...

Except that MG ply isn't necessarily any more rot resistant than exterior grade ply, both can and will rot when wet. In good construction neither will be wet though.

I'm not saying they are equal, MG is better, but depending on what MG product you buy it may be no more, or even less rot resistant than what you pick up at Lowes.

I will say that more and more manufacturures use PT MG ply now.

 

[iSteelHead]

Re: Marine Grade Plywood Debate Thread...

Yes, but..Lets just think. House's are a good example, your house is always being battered by the elements. Sun, Snow, Sleet, torrential downpours, winds, etc..whatever it maybe. One thing your house does not do and should not do, flex. A boat flexes while in water, and is constantly working, while in use. Yes, i am sure your house is always in use. I highly doubt your house has ever run aground, has ever been jockeyed on a trailer, or in choppy waters. I think that by MGP having no voids gives more rigidity to the structural integrity of the Boat. As for being less likely to rot, I believe it to be true. Think about it. Guy A.) buys his wood to make his house from Wal-mart. Guy B.) buys his wood from Lowes. 15years later, "A's" house is leaning and rotting. "B" is still sitting pretty with a structurally sound house, not having to worry about anything for more years to come. There is a difference in quality, natural resistances, and tolerances. Look at mother nature, and the forest. Some trees are meant to last, and some are meant for looks. Get my drift?

 

[iSteelHead]

Re: Marine Grade Plywood Debate Thread...

I agree with you Ondavr. It is all about the use it will see, and personal preference. I just am stating what I believe to be the reason for it to be used.

 

[ondarvr]

Re: Marine Grade Plywood Debate Thread...

The wood in fiberglass boats isn't used in the same way as it is in wood boats, or a wood house. If the structure is made of wood, and depends totally on wood for strength, then as I stated a couple of posts ago, you choose the wood to fit the need. For the most part ply is used for a low cost, easy to work with and durable core in fiberglass construction, and while the strength of the wood may be factored into the final product, the structure isn't totally dependent on the wood and in many applications can survive without the wood. In many of it's uses in F/G boats a lower strength core could be used, but the cost is so much higher for the lighter lower strength products they aren't used.

The wood in F/G boats fails due to rot and the poor workmanship that leads to it, not from the weakness of the wood.

By the way, I use PT MG ply.

 

[iSteelHead]

Re: Marine Grade Plywood Debate Thread...

Ya post #35. I said I agree with you, and Yes. I read your post above. Again this is why I said I agree. Post #29 is your post. stating what you said. I guess for redundancy sake. We both agree with one another.

 

[ondarvr]

Re: Marine Grade Plywood Debate Thread...

I would say we do agree.

 

[iSteelHead]

Re: Marine Grade Plywood Debate Thread...

Lol. I like your style.

 

[Cadwelder]

Re: Marine Grade Plywood Debate Thread...

Frequently Asked Questions: Products
What is Marine-grade plywood?
Marine-grade plywood is a specially designed panel made entirely of Douglas-fir or Western Larch. The grade of all plies of veneer is B or better, which means it may have knots, but no knotholes. The panels are sanded on both faces, and are also available with Medium Density Overlay (MDO) or High Density Overlay (HDO) faces. The maximum core-gap size permitted is 1/8 inch. Its exposure durability rating is EXTERIOR and the glue used is a fully waterproof structural adhesive. It is considered a ?premium? panel grade for use in situations where these characteristics are required, i.e., for boat hulls and other marine applications where bending is involved.

Marine-grade plywood is available in 4x8-foot sheets of 1/4, 3/8, 1/2, 5/8 and 3/4-inch thickness. Sheets up to 5x12 feet are also available. Available grades are A-A, A-B, B-B (face-back), MDO and HDO.

Marine-grade plywood is not treated with any chemicals to enhance its resistance to decay. If decay is a concern, it should be pressure-preservative treated to an appropriate standard.

The detailed description of veneer grades and Marine-grade plywood is contained in Voluntary Product Standard PS 1-09: Structural Plywood.

Here is a copy and paste from the APA website about Marine Grade plywood.