Choosing the right Plywood

[Reboot11133]

I stumbled upon this article when researching an epoxy I am planning to use to repair the rotted deck in my 1984 Bayliner. I am gong to use the West System of epoxy does anyone have any experience with this product. The literature (propaganda) looks good.

http://www.epoxyworks.com/18/index18.html

Scroll down to "Plywood Baisics"

 

[Coors]

Re: Choosing the right Plywood

I'm not a rep, but research MAS epoxy, and use cdx plywood.

 

[Reboot11133]

Re: Choosing the right Plywood

I'm not a rep, but research MAS epoxy, and use cdx plywood.

The MAS Epoxy is very similar to the West System. The cdx plywood is a rough plywood with voids and knot holes, is this what I need for a deck surface?

 

[drewpster]

Re: Choosing the right Plywood

I have read many opinions on this and I have found there are basically two camps of thought.
One group seems to rely more on the performance of the epoxy to coat and seal the wood as well as give it structural strength and rigidity. (composites)
The other group seems to think that it is best to use the best marine plywood with no voids and a smooth engineered surface on which to laminate the finish fiberglass surface.
Given the expense, I think it is best to use the method that best suits the job. For structural members like bulkheads stringers and such I think it is best to use quality marine plywood laminated with poly resins and quality fiberglass. For decks or finished surfaces to be gelcoated it may be best to build a composite structure to save weight.
In places where it is necessary to use lighter weight cores that need the best bond it may be best to use epoxy.
In areas that are inaccessible and likely to come into contact with water it may be best to use epoxy to prevent water intrusion with a marine grade core material.
I have found that each job has its own challenges and will need its own set of materials.

 

[TriadSteeler]

Re: Choosing the right Plywood

If you are able to afford the epoxy route it is definately the best sealer. I would however use ACX plywood. Go to your local lumber yard. IMHO, Lowe's or Home Depot doesn't carry the quality of ply you will be looking for. I purchased ACX for my transom and a portion of my deck and I have found it to be extremely devoid of voids.

 

[seven up]

Re: Choosing the right Plywood

The article recommends that pressure treated is generally acceptable for house projects but not on boats.

I know for marine use it (the pressure treated) has to be kiln dried after treatment, KDAT and at the minumum .025% retention. Not the kind of stuff available at the box stores.

The article talks of BS 1088 graded marine plywood.

If your boat needs a certification then a definite plan has to be utilized. Class D certification for ponds and small lakes is less strict.

Are there any Certified Composities Technicians in the house ?

 

[Reboot11133]

Re: Choosing the right Plywood

Thanks to everyone for your input!
I have committed to using epoxy. It was on sale and I am a sucker for bargains...come to think of it thats why I bought the boat in the first place...anyway plywood is still on my shopping list.

 

[tashasdaddy]

Re: Choosing the right Plywood

ACX is the best for finished areas. take the time to seal all edges before installation.

 

[marquette]

Re: Choosing the right Plywood

i went to Menards (upper midwest box store) to look for plywood to replace my floor and use for a casting deck. they had CDX, BDX and PT. the BDX had a smooth veneer on one side. they told me that they were the same exterior plywood except that BDX is one grade better than CDX because of the 1 smooth side but functionally they are the same. anybody know if that is true or false? if that is true it sure would be worth the extra $5 per sheet not to have to fill as many voids. i want to paint the decks on this boat rather than carpet or vinyl like i have on other decks. i have always used PT plywood before with good sucess but from what i have read on the forums unless i have 6 months to dry it i won't be able to get anything to stick to it. i only have about 2 weeks for drying time. so if anybody has any suggestions of how to get 2/3 of a sheet of PT to dry enough to get resin to stick in 2 weeks i would appreciate the help.

 

[CATransplant]

Re: Choosing the right Plywood

BCX will work, but if there's a real lumberyard in your community, ACX is so much nicer to work with on exterior surfaces. More expensive, of course, but...

 

[marquette]

Re: Choosing the right Plywood

what's the difference between ACX and BCX?

 

[jameskb2]

Re: Choosing the right Plywood

Each letter in the grade stamp or name is a quality of the veneer for each side and center of the plywood.

ACX is A grade veneer on one side, then C grade veneer in the middle then X grade veneer for the last side. This is a three veneer sheet, but often 5 or 7 ply sheets are labeled with the same three letter grade.

A is top grade finish veneer, for cabinets. B is smooth finish with very minor repairs. C is smooth finish with some noticeable repairs. D is semi smooth to rough finish with noticeable to large repairs or voids. X is nearly considered "filler" stock, and will have large voids and little or no repairs.

Do a search for plywood grade types and read as much as you want.

 

[drewmitch44]

Re: Choosing the right Plywood

I think that as long as its not treated you are going to want ply with as manny ply's or plies as you can get. Treated plywood takes a long time to dry enough to let resin stick to it. Its really hard to know if it is dry enough to use in a boat if you are going to try to glass to it. There is really no science to figuring out if you have dried treated wood enough to glass to it. So its really not worth it trying to use that for boat restoration. Its like just rigging up stuff cause you can not be sure that the wood dried enough. Its a gamble if you use treated wood so i try to stay away from it. I have a sea ray as my main boat project that i have for myself but ive done a couple of smaller jon's and what not just decking them out and light weight ply works for me really well. I normally use aluminum angle on the tinnies for support for the decks and it works out well. Good luck!

 

[GregE]

Re: Choosing the right Plywood

...ive done a couple of smaller jon's and what not just decking them out and light weight ply works for me really well. I normally use aluminum angle on the tinnies for support for the decks and it works out well. Good luck!

Drew, what thickness ply did you use on those? And what was your maximum span between aluminum angle supports?

 

[drewmitch44]

Re: Choosing the right Plywood

Everyone seems to recomend 3/4 thick ply. I like to use 1/2" to keep the weight down. I can get a 7 ply 1/2 inch piece of ply in 4'X8' at my local blows, i mean Lows. I have never had a problem. The aluminum angle i use i get in square form. So what i mean is it is square when i get it in long pieces. It is square tubing aluminum. I angle cut the opposite corners of the enclosed tubing and that makes it angle aluminum. The pieces that i get are usually 12' long. Once i cut it it is one and a half inches from the corner. Verry light and i have riveted and also used stainless nuts and bolts to attach the structure to the ribs of the boat. That stuff is really easy to work with cause once it is angle at that 90 degrees, you can shape it however you want. Then once you have framework you can add the ply and glass it and attach it. The alum. angle also is great for when you make hatches for storage cause it works to make a structure for the wood door to rest on. Its kinda hard to explain. but ill add a pic. This was my 1st boat that i decked out. I still have it and catch bass like crazy off of it.

 

[oops!]

Re: Choosing the right Plywood

as you can see.....there is many opinions and options for you.....

i may add........in the early days of boat building....the manufacturers prooved just about anything would work......even old pallett wood as stringers.

dont over think this....

rule of thumb.......what ever you buy...try to dry it a few days.....seal it well...

what ever wood you use.....after its sealed well...(as long as it is not riddled with voids).......what does it matter???

 

[GregE]

Re: Choosing the right Plywood

Thanks Drew. Yea weight is the reason I asked. The lesser the better but I wasn't sure how rigid 1/2 would be. 7-ply sounds great. That's the key to that rigidity.

Now if some plywood and angle would help me in my bass catching....