A Question about CDX Plywood - Fine Homebuilding

As noted the letters refer to

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As noted the letters refer to the quality of the outer layers.  There's also exterior and interior referring to the glue.  Also the number of plies matters.  Cheap plywood may have only 3 or 4 plies.  You want at least 5 plies and 7 or 9 is better.  Then there are hardwood plywood such as oak, though only the surface plies may be oak.  Then there is Baltic Birch, probably the best for building stuff - 3/4" has 13 plies, 1/2" has 9 plies.

Stay away from CDX - that's usually too rough.  Some of the cheap stuff with labels like plytanium or sanded pine can be used, but I would use better if you can afford it - B/B or better.  Note birch and Baltic birch are not the same thing.

Paul

Plywood

There are 4 grades of ply A B C and D. C does not mean construction grade it's just a grade like grades in school !   The best is A the worst is D. An X after the grades means exterior which means the resin used to bond the plys together is waterproof or water resistant. No X means interior use only. You don't need exterior grade plywood for layout bench work. Both sides of a sheet have a grade . So A-C means one side is A and one is C . CDX means one side is C and one side is D and it's exterior. I use BC grade in my plywood bench work and have never had any issues in over 40 years of use on two layouts. ------------  Ken 

Sometime you'll also see "One

Sometime you'll also see "One Side Good" or "Both Sides Good" as additional plain English information..  ("Both sides good" may still have visible patches but will be smooth) You might also see "no voids" indicating any "holes" on the inner layers have been filled or patched, or "Cabinet Grade" (usually birch these days) and "Marine Grade" which is a step above even "AA No Void", usually out of woods like mahogany or red oak.

My dad bought a two inch thick piece of Marine Grade to replace the transom in a boat that had been chewed by squirrels. It was "special order only".

Don't ask.

It's the reason we declared war on the pine squirrels and bought a .22 pellet rifle.

thanks

Thanks all, anyone have any idea what the '+' symbols were about? The woodworking site didn't explain that either.

"I use BC grade in my plywood bench work and have never had any issues in over 40 years of use on two layouts."

Thanks especially for that, topical advice like that is why I didn't just google for the info in the first place but started a thread.

+ and - signs on plywood grades

refer to plywood transitions to track grade provided by spline construction.  It changes with the direction of the locomotive.  Ie. it is + when the locomotive starts ascending the grade and - when the locomotive starts descending the grade.  The plywood makes for an easy transition to the spline gradient section.

Nick

P. S.  HD used to have some really fine birch plywood that I used a lot and liked.  I’m still using scraps of it.  Letting plywood sit and acclimate in situ helps fight expansion and contraction with changes in humidity if you can wait.

I used

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1/2 inch 4 ply BC on my layout construction in a basement 20+ years ago and never had a problem. 1/2 inch is more than sufficient for a railroad if it is supported properly and you don't plan on walking on it. ( I know a guy who has to walk over his yard engine terminal to rerail cars because it is about 6 ft wide at that spot)

Espee over Donner

home depot vs. lumberyard

The OP is shopping at Home Depot - if you check their web site you'll see how different their plywood world is from the good ol' days of A/B/C/D, 1/2", 3/4" etc. 

If you actually go into a Home Depot to see what you're getting, you'll be even more confused. 

Sorry if this isn't helpful Eastwind, but I'm just as bewildered as you are!

Jeff Allen

Start with a good foundation...

You can have the best scenery in the world, a great operating scheme, bullet-proof trackwork, and flawless wiring, but if all of that is sitting on an unstable base, it's going to suck. 

I used 3/4" premium Birch cabinet-grade plywood because it was the best that was readily available. I used the same stuff in 1/2" for the helix where I have supports about every 12" and needed the clearance, but I wouldn't want to use it for the main layout myself. You could, but you'd need lots of support. 

Randy

"anyone have any idea what

"anyone have any idea what the '+' symbols were about? "

  I think it means the grade was improved by filling and patching C+ would be C grade wood improved somehow.           You'll also find various  numbers on some sheets specifying it's structural suitability, dates of manufacture, mill or trademarks, etc. Hardwood plywood also uses a letter/number notation where the letter is the face and the number is the back side.  So AC would become A3.  I've used a lot of plywood over the years so I  don't go by the numbers as much as by the feel and appearance.....DaveB   

If you don't want issues...

I use HD only for my framework or benchwork, like 1"x3" or 1"x4". They used to call it #2 Pine now they call it common board. The better wood they call 'select pine' and of course charge more. I went to the HD near my home in So. Florida and spent close to an hour going thru 50+ pieces before I found 8 of them. Since I don't have grades or anything with risers, I went to the lumber yard and they made my cuts on 1/2" AC plywood. I paid more, but the wood is great. HD carries BC plywood and when you look at it, it makes you shake your head in disgust. They sell something called Sandeplywood, and while the tops look good, I read some online reviews that were less than stellar. I did use their 2"x2" wood for my legs and that wood is pretty good. Comes in 8 foot lengths. 

Best bet is the lumber yard for your needs. 

Neal

Plywood

Most places only carry CDX or AC when it comes to just regular old plywood. CDX is rough and used for a lot exterior work. AC is also sometimes known as Good One Face, because it has one good face and one rough one. Now, not all AC plywood has an actual clear face, some of it has little football shaped plugs that have been put in place where a knot was. 

The other option is going with a cabinet grade plywood, which usually comes in birch, oak, pine (or white wood), and sometimes poplar. These are ALWAYS more expensive than AC or CDX.

And barr_ceo, Marine grade plywood has always been expensive. The cheapest I can ever remember it was a 1/2" x 4' x 8' sheet being $56.00. I can only imagine what a 2 inch thick sheet cost!

For more information, please visit melamine sheets for cabinets.