non marine grade okume

[jmack]

I've been lurking about with plans in hand. I'm not ready to start construction yet but would like to get materials together.

My question- I found some okume plywood at a really good price- 1/2" for around $30 per sheet. Looks smooth on each side with no visible voids on the edges. Distributer states it's not rated as marine grade but it is rated for exterior use. Can I use this for my weekender, should I buy 1 sheet and do a boil test? Looking for input.

Also the same distributer recommended some ACX Radiata from Argentina for marine usage. Not as many plys as the okume. Anyone familiar with this product?

Thanks in advance

Jim

[Barry Pyeatt]

Hi Jim, Welcome and don't be shy. Just jump right in.

What are you building? Do you plan on keeping it in the water or on a trailer most of the time?

While Marine rated ply is the preferred way to go, it really is the way to go for those boats that are going to be "in the water" for longer than just a few days at a time at the most.

Do a boiling water test? Only if you feel that there is a question about it failing. Odds are it will fail along a glue line. Exterior glues are not necessarily rated for boiling water. They are rated for exposure to the elements.

The marine rating standards are to assure that that product meets or exceeds an accepted standard and they will stand behind it for marine use. What may be essentially the same product without the rating is often sold as well but rated for exterior use only. It may have other small differences that would keep it from being rated "Marine". Exterior rated Okume would be preferrable in my mind to other ACX branded or non-branded, simply because of the more plys. If no visible voids on any edges it is probably pretty fair product. The price difference on a boat that will spend most of its life on a trailer and just visit the water for short periods isn't going to be subject to the same issues.

I have no experience with that imported ACX nor have I seen anything on it from anyone using it for boat building. But then that doesn't mean much other than it is realtively new and imported because it is less expensive than a domestic product. We don't know what the actual plys are as far as woods and less plys is generally not as good for our use as more plys. I would be more concerned about freeze/thaw cycles and their impact on it with it bent and under stress. And interior voids.

[Barnacle Jim]

Ahoy Jim

[jmack]

Thanks for the quick response to all.

Forgot to mention I'm building a weekender which will live on a trailer most of the time. My crew (8 year old daughter and teenage nephew) are ready to start today. unfortunately, Honey-do's and some broken bones prevent me from starting right now.

Thanks again

Jim

[jmack]

Okay, I did a boil test on a sample of the Okume 1/2" and the 1/2" ACX Radiata plywood. After 30 minutes, I was able to pull apart the Okume while the ACX maintained its integrity.

Question- does standard exterior grade plywood delaminate after a boil test? The price on the non-marine Okume sure looks good but, am I wasting my money if I use it?

[Barry Pyeatt]

I'm afraid that there are just too many variables and unknowns about all the various exterior products out there to make any definite assumpitons or conclusions.

The problem is one of unknowns. We don't know the wood(s) being used, the glues being used or the country of origin for them. We also don't know if they are being manufactured to rating standards that are accepted by the construction industry and/or codes here in the US or Canada.

Over the last few years, the quality (generally speaking) of construction grades of plywood have gone down hill. The species of wood used on the interior plys is lower in quality than before. The quality of the grading system seems to have changed to lower standards or at least the product has changed.

For example, 1/4, 3/8, 1/2 and 3/4 plywood isn't those thicknesses any longer, it is thinner with the face veneers thinner than in the past. The core plys are of lesser quality veneers and thicker than in the past. This unfortunately is pretty much true across the board in the US and Canadian plywood industry. The products are still fine for their intended use, construction of buildings and related projects where they are primarily used as interior underlayment, or sheathing. For the most part they are covered by a myrid of other products that protect them from the elements and they are seldom subject to bending stresses. Voids are not an issue unless under a countertop laminate or vinyl floor.

So when we try to select a product to use for boat building it is a compromise unless we select a rated marine product designed with our use in mind.

As such, I would opt for more plys with known woods, interior core plys and exterior plys, exterior glues and outer plys as thick as the inner plys. Avoid the thin exterior plys with thicker interior plys if possible. I would tend to avoid woods that are known to be weak for boat building such as pine plywoods.

Since it is a material investment and you are considering the safety and well being of your family as a primary consideration. I would opt for a bit more of an investment if you can find known quality plywoods to use.

I don't base a whole lot on boiling water tests done out of lab conditions personally. I would look at industry standards and ratings and decide if I was willing to accept the questionable (due to unknowns) for something that I could feel a lot better about.

The cost of the plywood difference is still relatively low compared to your totel investment in the project. I would look around some more and make some more phone calls before deciding. Do some research other than just asking opinions on the forum(s).

Good luck!

[Barnacle Jim]

Ahoy Jim,

I remember well when I chose the plywood for my hull and how confusing it was. Sorry the dishwasher test did not turn out for you. Ours turned out OK. Most likely we used a different product.

A friend of mine who lives across town used Crezon for his hull. That's the same stuff used to make highway signs. His boat looks great. If I ever build another boat, I just may give Crezon a try. Here's a link with some information. Crezon has the same adhesive as does marine plywood.

Others on the board may have some better insight, but the stuff looks good to me.

http://www.greatnorthernlumber.com/crezon.htm

[Barry Pyeatt]

A web search on the Radiata plywood. will bring up a whole lot of varying information. There are a lot of different grades and standards for it depending upon its end use. (Apparently there is a marine grade Radiata, according to Chinese mfg. index)

The pine logs are actually from New Zealand and then exported to China, Chile, and several other countries for plywood mfg. Some of the exterior grades from some sources are made with essentially the same exterior class adhesives as exterior grades of plywoods made here and in Canada.

Pine in New Zealand is far different (and superior) product than most of the white pine lumber and pine plywood mfg. here.

It would seem that there is some really good stuff and some average qualtiy and of course some which it might be hard to tell. The vast majority of it seems to be in BC and lower construction grades.

Does this come from Dixie Lumber in San Antonio? I'm sure that they will give you more information if asked. But then they apparently also sell MDO plywood which could be a good choice since it is used for highway signs which are exposed to the weather year 'round. It has a resin impregnated paper surface which would make it quite resistant to checking and in theory could just be painted without glassing. But I would still glass the exterior surfaces.

[jmack]

Hey Barry,

The distributer is dixie ply in the Dallas area. Also I've heard of MDO but I'm not sure how well it would perform for use on a weekender. Input anyone?

[Barry Pyeatt]

There have been several builders use MDO with good results. John Teetsel built his Weekender stitch and glue using MDO and is a firm believer in the product. He joined the bottom sections with biscuits. He has some photos posted in the gallery. I've seen some postings on various forums of others using it with good success.

The primary advantage it may have is that it will hold up under almost any weather conditions and with the resin impregnated paper coating it will not check. It has good interior plys with fewer individual butt joints on the interior plys. This is primarily due to its intended use. 24/7 in the weather. It gets it all and will hold up for years of exposure with just paint as a coating.

The only drawback I've seen, but those using it don't seem to mind, is that when you bend it much the inside surface on the bend may wrinkle just a bit. Not a big deal as there really isn't that much severe bending but for the cabin front.

I think the ease of finishing and overall structural integrity would be worth a serious consideration of MDO for the project.

I would still look for 5 ply 3/8" material rather than the 3 ply with thicker interior ply. Then use the best surface on the inside where it will get paint vs. exterior which will get glassed over.

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