MDO Wood Question

[Yacht Dr.]

Re: MDO Wood Question

I know this is off topic 74bayliner .. but have you seen a boat (trojan) called the "Enterprise" ?

YD.

 

[74bayliner]

Re: MDO Wood Question

No I haven't... But interested now

 

[NSBCraig]

Re: MDO Wood Question

A tabbed and bedded in stringer is not spanning a distance. A span is like a bridge, the distance unsupported between two points. So that shouldn't rule the product out for use as stringers.

Let me ask you something, so it's ply wood with either one or both sides, where the outer ply is replaced for finish appearance? Since your not using it for this purpose, which it was made for, your using it as a bonding agent between the plywood and your glass?

But is it stronger than the normal layer of ply?

So are you using two layers of double sided MDO to make a transom? Which would replace two inside layers of ply with the exterior finish layers instead of the structural layers of ply?

Are you using the specially made marine ply with the MDO surface mentioned in the pdf or just the regular ply core?

How durable is this outer surface really? The pdf says if exposed to weather it needs all the same treatment as regular ply, prime- paint- and edge sealing.

I know it's been said before that you save some resin since it doesn't soak in, but besides that savings I'm not understanding the benefit for most build rebuilding applications. I do see some though.

 

[74bayliner]

Re: MDO Wood Question

So are you using two layers of double sided MDO to make a transom? Which would replace two inside layers of ply with the exterior finish layers instead of the structural layers of ply?

I dont know... thats why i was asking if it would be ok to use that. The more i hear about this stuff the more i think to just use exterior grade instead... i went to home depot for something else yesterday and looked at some of the exterior grade... price is not much different roughly 40 bucks a sheet. that may be my best course of action.

Are you using the specially made marine ply with the MDO surface mentioned in the pdf or just the regular ply core?

From the MDO i saw at the lumber yard it was not special marine ply, just regular MDO with finished surface on both sides

 

[NSBCraig]

Re: MDO Wood Question

I don't know either, I'd use exterior grade.

 

[Woodonglass]

Re: MDO Wood Question

A tabbed and bedded in stringer is not spanning a distance. A span is like a bridge, the distance unsupported between two points. So that shouldn't rule the product out for use as stringers.

This is somewhat misleading. Stringers in a boat are very similar to Floor Joists in a house. They are subject to flex from the hull and serve as support for the floor/deck of the boat. A 16' Length/Span of plywood in a boat must undergo similar engineering calculations to ensure that the loads placed on the stringer will not be enough to cause it to fail. With MDO using Resin as the outer layers of the product MIGHT (I don't know) make it somewhat weaker than the conventional Wood laminates used in the outer layers of regular ply when used as stringers vertically. On a Horizontal plane i.e. Decks. I'm quite certain it is a very good product for marine use.

 

[NSBCraig]

Re: MDO Wood Question

But, a stringer is fastened all along it's distance to the hull and maybe the deck/sole.
Which makes them not really at all like a floor truss,rafter, header or bridge.

I was simply stating that this alone does not rule it's use out.

The outer layer of MDO not being designed as a structural layer, but as an appearance layer should be considered in all applications.

As should wether or not you want to use the marine specific layers or just the exterior grade layers inside.

Then I guess you'd have to consider if it's the structure, if the laminate as a whole using the MDO as core is or if in fact you wanted to just go ahead and use more layers of 1708 to make fiberglass stringers using the MDO as extra strength left over inside your fiberglass stringers.

The more it gets discussed the less uses I actually see in using it though.

 

[Georgesalmon]

Re: MDO Wood Question

I tnink NSB is correct. The core does not matter as much as the fiberglass. Many largs boats have hollow or foam cored stringers. When using any kind of wood core (I prefer treated plywood but it is hard to find any that is dry) I've found that drilling lots and lots of small holes in it (1/8" to 3/16") makes the glass adhere better and longer. Think about 100's of tiny nails of resin holding the glass to the core. Even when horizontal resin will flow into those holes. Any single one will not have much strength as resin only but the cummulative effect is very strong. I drill the holes about 2" apart.

 

[Woodonglass]

Re: MDO Wood Question

I stand corrected. The Glass IS what provides the overall strength to the stringer system, not core material. You can and some have even used cardboard in the past. I apologize for dis-remembering this important fact. Thanks for helping over this Old-timers moment. But as always to have to remember I am just an...

 

[Yacht Dr.]

Re: MDO Wood Question

The outer layer of MDO not being designed as a structural layer, but as an appearance layer should be considered in all applications.

As should wether or not you want to use the marine specific layers or just the exterior grade layers inside.

Then I guess you'd have to consider if it's the structure, if the laminate as a whole using the MDO as core is or if in fact you wanted to just go ahead and use more layers of 1708 to make fiberglass stringers using the MDO as extra strength left over inside your fiberglass stringers.

The more it gets discussed the less uses I actually see in using it though.

When I called up the Rep for MDO he said the Surface layer is ready to accept Most resin coatings/builds.

Yes .. as a structural coating. From what I understand the paper backing is Completely compatible with Poly or Epoxy post lams.

The coating itself is ready to accept 70% of New Bond Coatings.. It is NOT a saturated coating that you have to do any other prep for..apply your new coatings right out of the box.

I tnink NSB is correct. The core does not matter as much as the fiberglass.

This will depend on what application we are talking about.. The core Does matter in most cases. its just How it affects your build that is a variable. .. foam/board/wood..etc ..

I stand corrected. The Glass IS what provides the overall strength to the stringer system, not core material. You can and some have even used cardboard in the past. I apologize for dis-remembering this important fact. Thanks for helping over this Old-timers moment. But as always to have to remember I am just an...

No..I think you were right on..No reason to stand corrected ..

YD.

 

[Scott Danforth]

Re: MDO Wood Question

a sandwich is only as strong as the meat and the bread together

 

[NSBCraig]

Re: MDO Wood Question

When I called up the Rep for MDO he said the Surface layer is ready to accept Most resin coatings/builds.

Yes .. as a structural coating. From what I understand the paper backing is Completely compatible with Poly or Epoxy post lams.

The coating itself is ready to accept 70% of New Bond Coatings.. It is NOT a saturated coating that you have to do any other prep for..apply your new coatings right out of the box.



This will depend on what application we are talking about.. The core Does matter in most cases. its just How it affects your build that is a variable. .. foam/board/wood..etc ..



No..I think you were right on..No reason to stand corrected ..

YD.

You lost me once again.

So your saying the rep told you it was a structural layer and it made sense to layer it in your laminate? This is contrary to the pdf's info. Which makes you wonder why they don't use more layers of it in the product, except for that it's an appearance layer.

Did he tell you to special order the marine version of MDO?

How is this layer supposed to be better than a board with all exterior plys? What is the benefit in your laminate? Except the little less resin to get started.

Do you not think that these factors should be considered when deciding to use a product?

As for stringers I said-

"Then I guess you'd have to consider if it's the structure, if the laminate as a whole using the MDO as core is or if in fact you wanted to just go ahead and use more layers of 1708 to make fiberglass stringers using the MDO as extra strength left over inside your fiberglass stringers.

Meaning you still can't rule MDO out for use as a stringer just because of what woodonglass and I were discussing about span. Though he is correct about thinking about it and definitely needs not to apologize. (though I loved the little pic)

Examples I gave were-

1. wood (or MDO plywood) as structure that's been waterproofed
2. wood (or MDO plywood) core as a grp laminate
3. wood (or MDO plywood) as a form from which you make glass stringers

All of which are possible ways stringers are built. (hopefully a clearer post)

We are all on the same page here right?

The product in the pdf is exterior ply with an outer layer (one or two) made for finish appearance for use in sign making etc. so you don't have to spend time and money making a good looking face. Just paint and letter. They of course have expanded the product uses with other uses and added a marine version (special order). But were still talking about exterior rated plywood.

 

[Yacht Dr.]

Re: MDO Wood Question

So your saying the rep told you it was a structural layer and it made sense to layer it in your laminate? This is contrary to the pdf's info. Which makes you wonder why they don't use more layers of it in the product, except for that it's an appearance layer.

Yes..that is what He was suggesting. The outer 'Paper skin' is only saturated with 30% resin.

So its ( apparently ) Pre-ready to accept resin/glass/coatings without Any prep. Kinda like buying ply with only 30% resin coated FG mat. No need to sand ..just resin coat and start your lams.

Did he tell you to special order the marine version of MDO?

Nope..it was the regular C grade MDO. I guess the stuff is C grade ply with Doug Fir outer finish..then the paper.

How is this layer supposed to be better than a board with all exterior plys?

Got me mate LOL .. I never said/suggested that MDO was "better" than other ply builds.


Dont get me wrong here .. If you look in the archives I was the first one to suggest NOT to use MDO when another member was introducing its use as a "possible" alternative. I suggested that More data was needed to fully understand how and where MDO could be used for Any application in our restorations.

Im not suggesting its use at all.. I am trying to point out that MY personal investigation on using this material does have qualifications for marine use.

I dont see any specific reason to use 'alternative' board such as MDO .. but I think ( after consideration and consultation ) that the Material Can be used without harm.

But..if you ask me .. MG is still the best of the best ..

YD.

PS. I hope WOG feels vindicated now ..

 

[NSBCraig]

Re: MDO Wood Question

Oh so it would seem were all running out of reasons to use this product.

Yeah I remember you saying you didn't think it was a good choice, I just keep seeing it brought up so I wanted to give the idea some thought.

 

[74bayliner]

Re: MDO Wood Question

well all i know is i am glad i posted this. I have learned more from this post than i have ever known about MDO. Thank you all for your input

 

[Yacht Dr.]

Re: MDO Wood Question

Oh so it would seem were all running out of reasons to use this product.

Yeah I remember you saying you didn't think it was a good choice, I just keep seeing it brought up so I wanted to give the idea some thought.

It does seem so..unless it was Free .. .. I still would not use it for Structural..even though it seems viable for use in marine applications. There are cheaper and better ways to build a boat.

I would however use/save it for my builds on bookshelves and wall shelves.

YD.

 

[NSBCraig]

Re: MDO Wood Question

That's what I was thinking- shelves, cabinets etc.