MDO Wood Question

[74bayliner]

I have decided that MDO is a good price as i can get it for roughly 40 dollars a sheet of 3/4 inch by a supplier.
my question is according to multiple websites that this wood is already coated with a fiberglass resin to withstand weather such as water etc...

I went to the supplier yesterday and took a look at the wood.
It looks nice but it is already coated with something. question is
Would this wood need to be covered in resin before i put CSM on it to waterproof it more?
Will the Resin stick to it or get "Soaked in" ?
And will fiberglass stick to it well... I understand that it will probably soak in around the edges as they look like normal plywood but the top and bottom looks almost as if it was coated with gelcoat ... a hard flat surface.

So if i was to get this 2 sided MDO with the nice finish on both sides. And i cut stringers out of that, would i need to just encapsulate the stringers in csm, or just fiberglass "Cap" the ends so it would not have ends that were exposed.

 

[glnbnz]

Re: MDO Wood Question

Bump...I am curious to opinions on this... anyone??

 

[Woodonglass]

Re: MDO Wood Question

You have to scuff the surface with 60 grit to get the resin and glass to bond. You must coat the edges. You do not have to precoat the surface. You don't have to put a layer of CSM on the bottom layer but I would recommend Painting it with Oil Based enamel.

Here's the info on MDO/HDO...


http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=1&ved=0CCcQFjAA&url=http%3A%2F%2Fwww.plumcreek.com%2FPortals%2F0%2Fdownloads%2FproductInfo%2FMDO.pdf&ei=OJ2FT42PBsXY2QXN5PDhCA&usg=AFQjCNGLwXNzLxdgc8mzjpD3Y5Ra2LN_5A&sig2=T01despH3Wy0f30zU5I2mA

 

[74bayliner]

Re: MDO Wood Question

Hey Mike,
Thanks for the PDF that really helped me understand more about the wood.
I will most likely scuff the surface like you said but i will coat the whole board with resin than lay down mat just because i am going to purchase a large quantity of both mat and woven that i wont be worried about running out. I dont like the idea of using oil based enamel i dont know why it is just not a preferance for me.
But thank you for the advice
-vlad

 

[Woodonglass]

Re: MDO Wood Question

The MDO has been used for Years for Painted Road Signs. Holds up extremely well with just a painted surface. You can scuff and lay the CSM and you will have a TANK. Totally up to you.

 

[boat_beginner]

Re: MDO Wood Question

Is there a large difference in the weight of MDO compared to marine ply or arauco ply? I thought I have heard that the MDO is a lot heavier, but can't remember where I heard that or if there is any truth to it or not.

 

[Yacht Dr.]

Re: MDO Wood Question

You want to use MDO for the stringers and other structural components ?

Im not sure is Woody understood this before he mentioned 'Oil based products' ..

YD.

 

[74bayliner]

Re: MDO Wood Question

From the research that i have done i have found this: but it may not be the exact truth just an estimate
average weight of 4x8 3/4 plywood is @70 lbs.
average weight of 4x8(ish) 3/4 mdf is @96 lbs
Douglas Fir 4x8 3/4 plywood is @ 75 lbs

"Medium- and High-Density Overlay Plywood (MDO and HDO)
MDO and HDO consist of a core material, like laminated fir veneer, overlaid with a pressed fiber material. In short, this is a typical veneer core plywood (common plywood) with an MDF surface. This gives the best of both worlds; the weight is lower than a full MDF, but the surface is more stable than a veneer core plywood."

But from what i gathered at the lumber yard i went to they were all roughly the same weight to me but it seemed that one of the marine ones they showed me... okuma or some wierd name was heavier... but than again i dont know much about wood

 

[minuteman62-64]

Re: MDO Wood Question

Don't know about use for stringers, but, the bench seats in my 1982 era boat are single sided MDO that were originally just given a coat of paint. The paint is worn off in places but the resin bonded surface is still in great shape, just waiting for another coat of paint.

 

[Woodonglass]

Re: MDO Wood Question

Whoa, YD to the rescue again!!!! I do NOT recommend MDO for Stringers and have not seen it recommended by anyone here on the forum. My personal opinion is it's OK for transoms and Decks but stringers, I think you'd be much better off using Araucao Plywood or plain ext. Grade Ply or underlayment ply.

Thanks Again YD!!!

 

[boat_beginner]

Re: MDO Wood Question

This will probably sound stupid, but why doesn't anyone recommend MDO for stringer use?

 

[idonthaveaname]

Re: MDO Wood Question

This will probably sound stupid, but why doesn't anyone recommend MDO for stringer use?

Not stupid! I was wondering the same thing. I'm not considering MDO, but it would be good info to have.

 

[ezmobee]

Re: MDO Wood Question

This will probably sound stupid, but why doesn't anyone recommend MDO for stringer use?

I wonder the same thing. It's good strong wood right? Heck it's probably stronger than Arauco. Is it a glass adhesion issue?

 

[Woodonglass]

Re: MDO Wood Question

In my construction business years ago, I used a lot of it. I thought it would be great for boat decks and it is. I researched it and contacted the APA and some mfgs. They agreed that for spans under 5' and widths greater than 12" it would work great. Stringers are typically longer than 5' and less than 12" tall. Transoms on the other hand are usually 18" to 24" and 4' to 5'. Decks No Problem. They explained it was because of the resinous outer laminations not withstanding the flex of the greater span. Bulkheads are usually Ok too unless they are not very high. As long as you scuff the resin outer layer with 60 grit there should be no problem with adhesion. HDO is even better for Marine use but a bit more pricey. We used it for concrete forms and could reuse them multiple times. Concrete would not stick to it ever. Having said all this, and thinking about some recent statements ondarvr has made, boat hulls under 20ft don't have all that much flex sooo... you might get by with using it for stringers in these smaller boats. Just passing on what I have learned. It's your boat, you can do what you think's best.

 

[74bayliner]

Re: MDO Wood Question

Ok Woodonglass time to explain yourself... admit it you get a slice of the pie for every Araucuo sheet sold!
Just kidding please explain.

EDIT: You have a quick trigger finger!! i posted this almost same time as you.

 

[74bayliner]

Re: MDO Wood Question

Thank you for the knowledge WoG. I will consider using something other than MDO for the stringers but i think i am sold on MDO as far as the deck and transom are concerned

 

[Yacht Dr.]

Re: MDO Wood Question

I wonder the same thing. It's good strong wood right? Heck it's probably stronger than Arauco. Is it a glass adhesion issue?

Yup ..

Its in the prep of the MDO that would make it hard to use properly.

The 'skin' of the product would/might hold to the resin applied..but how well is the paper skin adhesion to the MDO going to hold up. ( Delam )

I trust my glass to wood more then I would trust my Glass to paper to wood.

YD.

 

[Woodonglass]

Re: MDO Wood Question

In all my years of using it for Concrete forms, and believe me it was ABUSED out in the elements, I never saw the "Paper Skin" delam from the wood, Never!!! My concern for boats is how well the Polyester will adhere to the scuffed resin layer of the MDO. The MFG says its fine and it's been used in the wood boat industry for over 4 6 but they use epoxy most of the time. I'm not the least bit worried about the product delaming just the glass delaming from the resinous outer layer of the MDO. I have no Direct First hand long term experience to back up the claim that it will work. Only what the mfg says.

 

[Yacht Dr.]

Re: MDO Wood Question

After an hour long phone call to one of the MDO/HDO 'builders' I have come to some conclusions..

HDO is no good for boat repair .. its too saturated with resin. Not enough surface to accept the resin..

MDO has only 30% of the coating for the substrate. Meaning that the other 60% can be used for a bond of resin.

Basically..the MDO is a tiecoat of ply-application of surface coatings without Any failure.

Your resin/glass will not release in a form of delam using the MDO from what the Rep said..

If this is true..then MDO might be good for stringers and bulkies ..

I might have to insert foot into mouth. ( possibly both feet if Woody reads this ) .. but thats why we are all here .. to learn more about products at hand and up to date on procedures ..

YD.

 

[74bayliner]

Re: MDO Wood Question

Very Good information from Everyone. I have personally visted about 6 lumber suppliers this week and have a few more to go that are near by checking out quality and prices and also using what i learn here to sound smart so thank you all for your help my final decision will come to light when that part of my rebuild continues on my rebuild thread.