Seriously! Marine or Pressure Treated???

[ondarvr]

Re: Seriously! Marine or Pressure Treated???

I think these parts of the discussion are very important, they bring out the finer points and details of products and methods. Frequently there are too many misunderstandings, myths, or just bad information floating around that are accepted at face value as being true and they lead people down the wrong path. .

Whatever the subject I try to find the facts and science behind the issue or question and base my decision on how to deal with it on what works and why. This doesn't mean there is only one way to do the job, just lets you know the pro's and con's of each method or product so you can choose the approach that works best for you.

 

[Mark42]

Re: Seriously! Marine or Pressure Treated???

Hey look at that some people do make some.

How come that's not what you suggested?

.....

Because the pressure treated plywood available at lumber yards will work just as well at a considerable savings.

 

[North Beach]

Re: Seriously! Marine or Pressure Treated???

Ondarvr,
You hit the nail on the head with your last post. I grew up working charter boats and working crab boats on the chesapeake bay. We decided to get this boat and share some of the great times on the water with our now grown children. This will be a family boat and we'll have some great time in it I'm sure.

However, I have no background in how boats are put together. My years on the bay were all spent in bay built wooden boats that someone else worked on. I was way too young to be involved in that part of things. So this site was recommended to me by a friend who recently restored a 63 Yankee Clipper.

I want to put this boat back into the condition it was when new or better and my friend told me that I could ask questions and throw out ideas and the folks here would not hesitate to share their experiences with me. He was absolutely right!

The heated nature of the thread is testimony to just that. All a guy can do is take it all in and try and make an informed decision that works within his ability or resources.

Thanks to all of you for your expertise and opinions.

 

[NSBCraig]

Re: Seriously! Marine or Pressure Treated???

Because the pressure treated plywood available at lumber yards will work just as well at a considerable savings.

No it's not the same product and what makes you think you can dry it out enough. That greenwoods big thing was that they dried it for you pre delivery.

You don't really believe that PT doesn't rot do you?

I just replaced a 4x4 light post that was two years old and rotted off at ground level.

I have a ply of PT landscape timbers back by the shed that are not only rotted but ate up by bugs.

How many rotted fence posts are there, or decks, or playground, or docks...

Wood will rot no matter what you do, it's part of life.

All you can do is hedge your bet the best you can.

That is done by sealing it.

ondarvr taught me a bunch about not needing to use epoxy and that it's a matter of just doing it right for the system you use.

"Using regular, non-treated plywood is guarenteeing a future failure", is a nonsense statement cause using any wood product is guaranteeing a future failure if you don't keep up on and maintain the seal.

"If pressure treated ply is used, then minor failures of the seal will not cause failure of the plywood", is simply not true PT rots there for if the seal fails it fails. Sure it might last longer now that your seal failed, but it's real good odds that your seal failed cause you wood was wet to start.

Unless you do though testing with a moisture meter you can't begin to believe you have actually dried it out.

 

[sschefer]

Re: Seriously! Marine or Pressure Treated???

Dry rot is caused by fungi that can either be present in the wood at the time of milling or induced later by creating a suitable environment for it. The most prevelant fungi is Serpula lacrymans.

Pressure treating lumber at the mill kills the fungi and most other fungi that are present in the wood. The product that is most common for killing this type of fungi is a form of copper and depending on the composition it can be very effective.

Can dry rot occur in sealed wood?
Yes, if the fungi was present before the wood was sealed.

Can fungi infect pressure treated wood?

Yes but the chances are lessend if the wood is used without modification. If you cut the wood, the cuts must be re-treated with a solution such as "Copper Green".

Does it matter if Pressure Treated Lumber is dried?

No, if it is dried whole and uncut. By the time you dry it to 6-7% moisture it should have already had sufficient time to kill the fungi. If it is sealed at that point with a penetrating epoxy it should be o.k.

Why penetrating epoxy? Because the surface of the the wood is cut and sometimes sanded at the mill. This process leaves the cellulose pockets open and therfore susceptable to fungi. While most resins will seal the surface pockets well enough in most cases, a penetrating epoxy will pass beyond the surface and fill and seal most subsurface dry pockets that are most susceptable to fungi.

So, the question is still unanswered as to which is best. Pressure treated would be the best provided adequate care is taken to ensure that the intergrity of the pressure treatment is maintained.

Marine grade presssure treated lumber is supposed to be available although I've never used it. Marine grade ply is normally used in places where additional strength is need. You can, (and I have), coat it with "Copper Green" and then seal it with penetrating epoxy to attempt to thwart off fungi but there's no guarantee that it will work if the fungi is already present in the wood.

So, if you want the wood to last and you don't want to spend a lot of money on wood, you can glass it and essentially use the wood as a form that you do not remove. It can still dry rot but the glass will hold it together.

If you don't want to glass but don't mind using products like GluVit and "Copper Green" then go with pressure treated. It might not last as long a glass but it will probably last a good long time.

You should use marine grade if you need the extra strength such as in boats where the floor is an integral part of the structure. You can glass it if you want but for sure, you want to treat it with something.

 

[Mark42]

Re: Seriously! Marine or Pressure Treated???

No it's not the same product and what makes you think you can dry it out enough. That greenwoods big thing was that they dried it for you pre delivery.

You don't really believe that PT doesn't rot do you?

I just replaced a 4x4 light post that was two years old and rotted off at ground level.

I have a ply of PT landscape timbers back by the shed that are not only rotted but ate up by bugs.

How many rotted fence posts are there, or decks, or playground, or docks...

Wood will rot no matter what you do, it's part of life.

All you can do is hedge your bet the best you can.

That is done by sealing it.

ondarvr taught me a bunch about not needing to use epoxy and that it's a matter of just doing it right for the system you use.

"Using regular, non-treated plywood is guarenteeing a future failure", is a nonsense statement cause using any wood product is guaranteeing a future failure if you don't keep up on and maintain the seal.

"If pressure treated ply is used, then minor failures of the seal will not cause failure of the plywood", is simply not true PT rots there for if the seal fails it fails. Sure it might last longer now that your seal failed, but it's real good odds that your seal failed cause you wood was wet to start.

Unless you do though testing with a moisture meter you can't begin to believe you have actually dried it out.

Yes, pressure treated lumber does completely dry out. Why would you think it doesn't? My personal experience with p/t woods of all types is that they do dry completely through and through. And don't worry about applying polyester to damp p/t. Tests show it adhears nearly as well as on dry plywood. In fact, when pulled off, the wood separated from wood, not the polyester from the P/T wood.

And as is pointed out above, pressure treated lumber in contact with the ground is a different story. But I will share that last year I removed a fence at my Dads house we put up about 20 years ago. Out of 20 or so 4x4 posts, only 3 or 4 showed signs of serious rot, and that was at ground level. Below and above grade, the posts were fine.

I don't understand why you have such an aversion to pressure treated lumber. For the vast majority of members on this forum, there is no appreciable difference between plain old pressure treated from the lumber yard and marine grade. If I were doing a transom on a boat with twin 250hp outboards, I would probably use a marine ply for the strength, but for most boats on these forums, p/t will provide the strength they need with the added measure of rot resistance when water leaks in. Regular plywood will rot when wet in a matter of a couple of months. Even if you are able to seal it, it will not stay sealed very long. Water will get in.

Many members here have a budget to stick to. I believe it is a real dis-service to insist that they spend money needlessly on high grade materials that are overkill on their project boats. It is not uncommon for people to get into boating with a small boat, then upgrade to a larger boat. So why should they spend big dollars on high tech materials that they will only keep 2 or 3 seasons, then upgrade? It makes no sense. Let them save their money for accessories like PFD's and such.

Another way of looking at the situation is this: Many boats from the 80's and 90's were built with marine grade ply in the transom and sealed. Today people are ripping out all that brown mush that used to be marine grade plywood because the seal failed. Water gets in to the transom through the motor mounting holes, through drain plug fittings, through screws used to mount pitots, etc. The deck has battery boxes screwed down, oil tanks, and accessories. Water gets in. It can't be stopped.

 

[Mark42]

Re: Seriously! Marine or Pressure Treated???

One other thing.... Many members of these forums have used p/t ply and poly over the years. Do a search on this forum, it goes back many years, and see how many posts you can find where boaters complain about problems they had as a result of using pressure treated plywood and poly. See if you can find any posts about first hand experiences of delamination caused by wet p/t. I'm guessing that you won't find any because in all my years participating in these forums, I can't recall a single one.

Oh, yeah, you will find some people warning you not to use it, but I don't think you will find anyone posting their own failures because of it.

Of course, I could be wrong. Why don't you call me on it?

 

[Mark42]

Re: Seriously! Marine or Pressure Treated???

I found the tests of pressure treated ply vs regular ply for the purpose of boat building. It is a very short and interesting read. Here are the results of the test:

Results

The influence of the treatment and moisture content on fiberglass bondability was assessed by two measured results:

Whether failure occurred in the plywood or at the fiberglass/plywood interface
The load at which failure occurred
All tests on the untreated and treated specimens at the 65% relative humidity failed predominately in the plywood, indicating a good fiberglass bond. This indicates that the treatment did not have an adverse effect on bonding at this moisture level. Furthermore, the strength of the treated and untreated plywood were similar.

The effect of the 90% relative humidity led to some failures at the plywood/fiberglass interface indicating poor bond. This occurred for some untreated and treated plywood types.

These results lead to the conclusion that the most common treatment for plywood, CCA, does not adversely effect the bondability of fiberglass to plywood at moderate moisture content at the time of lamination. Elevated moisture contents, whether treated or untreated, adversely effects bondability.

Recommendations for using treated plywood for boat manufacturing will stress the importance to obtain properly redried material. Proper handling to minimize moisture exposure is also important.



Technical Services Division
September 1998

Read the entire article by the APA on the Glen-L website here:
http://glen-l.com/wood-plywood/fiberglass-plywood.html

This is another great article by the APA on plywood in boat building in general. These guys know plywood. You should read what they have to say.

http://boatbuildercentral.com/howto/APA_Plywood.php

 

[sschefer]

Re: Seriously! Marine or Pressure Treated???

Mark42 -- Re:fence posts -- Next time you need to set a fence post wrap it 2' up and around the bottom with 20# construction felt after weting that area and the end thoroughly with "Copper Green". Nothing will be permanent but in certain soil conditions where fungi and Ph is above 7 (acidic) this will help.

Also, if you are setting in concrete, crown the top of the concrete to help keep water away from the post.

 

[Mark42]

Re: Seriously! Marine or Pressure Treated???

Mark42 -- Re:fence posts -- Next time you need to set a fence post wrap it 2' up and around the bottom with 20# construction felt after weting that area and the end thoroughly with "Copper Green". Nothing will be permanent but in certain soil conditions where fungi and Ph is above 7 (acidic) this will help.

Also, if you are setting in concrete, crown the top of the concrete to help keep water away from the post.

Thanks for the tip. I was thinking of building a shed roof held up by 4x4 posts to store the boats under. That may be the trick to giving it long life.

 

[NSBCraig]

Re: Seriously! Marine or Pressure Treated???

Mark I don't have an adversion to PT. I just completely disagree with your adversion to using regular ply.

"Even if you are able to seal it, it will not stay sealed very long. Water will get in. " is nonsense plain and simple.

Why won't it stay sealed for long?

Why is the balsa core in my boat that was built in 84' not all rotted? I know why the transom rotted it was the stupid unsealed holes someone drilled in it and then the boat sat in the water for years soaking it up. Not cause it wasn't PT.

Everyone else seems on the same page about drying time. (If you believe your getting it dry, I buy PT wood of every variety very often I don't see it, oh and I have a moisture meter)

Or I could say it like this- Recommendations for using treated plywood for boat manufacturing will stress the importance to obtain properly redried material. Proper handling to minimize moisture exposure is also important.


And I'll stress- PROPERLY REDRIED

oops! says forget PT and us regular ply too.

Kaferhaus says his is still as good as the day he did it 15 years later (not PT)

Don S says just use good plywood.

Drewmitch44 agrees.

.......

I stand by my post-

Use regular old plywood.

No need for marine and no need for PT.

Any benefit from PT will be lost trying to seal it, remember it's been pressure filled with liquid you'll never really dry it out. It' s deep inside.

Just use regular wood and seal it either with epoxy or poly with glass reinforcement.

You can spend more if you want a pretty face but if your covering it that doesn't matter either.


You can stand by your crazy guaranteed failure if you don't use PT

 

[NSBCraig]

Re: Seriously! Marine or Pressure Treated???

Many members here have a budget to stick to. I believe it is a real dis-service to insist that they spend money needlessly on high grade materials that are overkill on their project boats.

Hey sounds like the point of not spending more on a wood deck then you need to for a tinny just use regular ply and seal it. huh?

 

[Mark42]

Re: Seriously! Marine or Pressure Treated???

Now you are just arguing, and not contributing anything of value. So I am done here. Believe what you want, do what you want. Have a nice time.

 

[NSBCraig]

Re: Seriously! Marine or Pressure Treated???

No I'm not just arguing.

You in fact have been for quite some time.

How long ago do he say he ordered marine ply and ask about sealing it?

But you just want to make crazy statements about everything else failing.

Marine PT as stated by the companies with links above is NOT the same as PT you get at the lumber store. One of the BIG differences THEY quote is how they dry it afterwards.

And the study you provided clearly states that it must be re-dried properly.

Pointing this out is in NO way "not contributing anything of value".

In fact we now know from your research and post that no thread about using PT would be right without including discussion on the correct way to do the re-drying. It was so important that the people doing the study felt the need to stress that fact.

 

[NSBCraig]

Re: Seriously! Marine or Pressure Treated???

The Boat Builer Central page you pointed at-

Treated wood products are readily available and are often used in construction where high decay hazards exist. Unfortunately, much of the treated plywood found in retail lumber yards may not have been redried to the degree required for boat construction. The following recommendations are geared specifically for treated plywood for boat construction. For best performance, care must be taken to specify and purchase treated plywood in accordance with these recommendations.

First, make sure the plywood cornes from a mill that is a member of APA - The Engineered Wood Association. That is your assurance that the mill is subject to APA?s rigorous quality assurance program.

Treating is conducted as a secondary process following the commercial treating standards written by the American Wood Preservers Association (AWPA). The most common treatment and retention level for plywood used in boat construction is CCA (Chromated Copper Arsenate) at 0.40 pcf retention. Other treatments for boat use are ACA, ACZA and ACQ.

AWPA Standard C9, "Plywood - Preservative Treatment by Pressure Process," specifies that the preservative-treated panel be redried to a moisture content of 18% or less, unless waived by the specifier. For use in boat manufacturing, the redrying of the treated plywood is essential to good performance when laminating with fiberglass. Treated plywood purchased from lumber yards is often used in construction applications and is not necessarily re-dried after treatment. It is essential for boat manufacturers to specify redrying.

 

[NSBCraig]

Re: Seriously! Marine or Pressure Treated???

Kiln drying to 18% seems to be the ticket

Not really a do it yourself type project.

 

[ondarvr]

Re: Seriously! Marine or Pressure Treated???

And Billp and I aren't even involved in this.

 

[NSBCraig]

Re: Seriously! Marine or Pressure Treated???

Oh I was just stating what was said earlier in the thread and in no way meant to imply we were in anyway having other discussions about it or any other thing .

Just that you said use regular ply. Not PT.

But seriously there should be a sticky made pointing out that Home Depot PT ply is not the same as marine PT ply and the plywood assoc. and research says not to use it in your boat. They stress it's importance so much that it might be important.

 

[fishrdan]

Re: Seriously! Marine or Pressure Treated???

Actually, someone should create a sticky that discusses the different types of plywood and their uses in boat building, precautions, advantages, disadvantages, characteristics, etc....

- interior plywood (inferior)
- exterior plywood
- ACQ treated exterior plywood
- CCA treated marine plywood
- marine fir plywood
- okume marine plywood
- cabinet grade plywood
- arauco plywood
- etc
- etc

you know,,, the good, the bad and the ugly...

 

[sschefer]

Re: Seriously! Marine or Pressure Treated???

Actually, someone should create a sticky that discusses the different types of plywood and their uses in boat building, precautions, advantages, disadvantages, characteristics, etc....

- interior plywood (inferior)
- exterior plywood
- ACQ treated exterior plywood
- CCA treated marine plywood
- marine fir plywood
- okume marine plywood
- cabinet grade plywood
- arauco plywood
- etc
- etc

you know,,, the good, the bad and the ugly...

That's a great idea!