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Discussion Forum

A Question about CDX Plywood

Jeff | Posted in General Discussion on December 4, 2003 04:01am

Hi all

I have a question to ask anyone, more for my curiosity then anything else.

I went to the yard the other day to buy some 3/4 in CDX.

I stopped in the office to ask the current prices and also asked about the glue.

I was pricing CDX and Underlayment for a job and asked if the glue was the same.

He told me no, the CDX used exterior glue and the Underlayment interior glue.

I went to the yard to pick up the CDX.

The CDX he gave me was the nicest stuff I’ve ever seen.

The yard guy said it was actually Underlayment that didn’t quite meet spec’s, so the manufacturer downgraded it to CDX.

The yard guy said that otherwise, it was all the same (Obviously with a better finish).

Needless to say, I was happy.

But, I am curious if any one knows the answer.

Jeff

 

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Replies

  1. joeh | Dec 04, 2003 04:58pm | #1

    Don't know about the glue, but how much did you pay for it?

    Joe H

    1. Jeff | Dec 05, 2003 12:44am | #14

      Joe

      $30.00 a sheet, and it hurts all the way.

      I'm glad I don't have any quotes for jobs out there that depended on the old prices.

      Only needed 9 sheets to finish up my last job before winter.

      All finished now, and snow just arrived this week.

      Jeff

  2. FrankB89 | Dec 04, 2003 05:10pm | #2

    To the best of my knowledge, at least here in the West, all plywood has been layed up with exterior glue since the late 60's to early 70's.  (Doug Fir ply, anyway)

     

    1. jimblodgett | Dec 04, 2003 05:47pm | #3

      Now here's an example of why I love this forum. 

      It has always been my understanding that "CDX" means the plywood has one "C" grade face, one "D" grade face, and was laid up with exterior glue, thus the acronym "CDX".

      I also thought any plywood that doesn't carry that "X" in its label, or clearly say "exterior" in its grade stamp, should be considered for use only where it will be protected from the elements from the time it's made until they tear the building down to build another strip mall.

      So now Notcher says he thinks differently than that, and I don't doubt him one bit.  And hopefully someone will chime in with some documentation about grading that will clear up a misconception I've carried all these years.

      Of course, with the continuing advent of O.S.B. sheet goods this isn't as critical an issue as it once was, but I'd still love to hear what others say. 

      This type difference between my long held beliefs and reality are exactly the same type of thing I enjoy about the "What's the Difference" column in FHB.  Many of the real basic articles provide similar revelations to me as I glance through them.

      1. User avater
        GoldenWreckedAngle | Dec 04, 2003 06:02pm | #4

        A common misconception is that CDX has an "Exterior" rating. It does not have an "Exterior" rating, it has an "Exposure 1" rating.

        The difference is that "Exterior" rated plywood is fully waterproof and designed for applications where it will have permanent exposure to weather or moisture.

        "Exposure 1" rated plywood has a fully waterproof bond but is not intended for applications where it will be permanently exposed to weather or moisture.Kevin Halliburton

        "I believe that architecture is a pragmatic art. To become art it must be built on a foundation of necessity."  - I.M. Pei -

        1. davidmeiland | Dec 04, 2003 06:20pm | #5

          Hate to ask, but how could any plywood be 'fully waterproof'?

          1. User avater
            GoldenWreckedAngle | Dec 04, 2003 06:30pm | #6

            Here is the APA's explaination: http://www.apawood.org

            What is Marine-grade plywood?

            Marine-grade plywood is a specially designed panel made entirely of Douglas-fir or Western Larch. The grade of all plies of veneer is B or better, which means it may have knots, but no knotholes. The panels are sanded on both faces, and are also available with Medium Density Overlay (MDO) or High Density Overlay (HDO) faces. The maximum core-gap size permitted is 1/8 inch. Its exposure durability rating is EXTERIOR and the glue used is a fully waterproof structural adhesive. It is considered a “premium” panel grade for use in situations where these characteristics are required, i.e., for boat hulls and other marine applications where bending is involved.

            Marine-grade plywood is available in 4x8-foot sheets of 1/4, 3/8, 1/2, 5/8 and 3/4-inch thickness. Sheets up to 5x12 feet are also available. Available grades are A-A, A-B, B-B (face-back), MDO and HDO.

            Marine-grade plywood is not treated with any chemicals to enhance its resistance to decay. If decay is a concern, it should be pressure-preservative treated to an appropriate standard.

            The detailed description of veneer grades and Marine-grade plywood is contained in Voluntary Product Standard PS 1-95: Construction And Industrial Plywood.

            Sample Specification For Marine-Grade:APA 3/8” B-B Marine Grade 4x8 10 piecesKevin Halliburton

            "I believe that architecture is a pragmatic art. To become art it must be built on a foundation of necessity."  - I.M. Pei -

          2. User avater
            GoldenWreckedAngle | Dec 04, 2003 06:38pm | #7

            Here is a Glossary from the APA that covers all their plywood ratings in depth. I learned more in the last two minutes of looking at it than I ever knew I didn't know.

            http://www.apawood.org/pdfs/managed/X505-R.pdfKevin Halliburton

            "I believe that architecture is a pragmatic art. To become art it must be built on a foundation of necessity."  - I.M. Pei -

          3. User avater
            IMERC | Dec 04, 2003 08:19pm | #9

            Almost every thing I thought I use to know about plywood doesn't apply any more... I use to think of plywood the same as Jim. 

            Thanks WA.. (said with a light touch of sarcasim? 

            Who ever invented work didn't know how to fish....

          4. User avater
            GoldenWreckedAngle | Dec 04, 2003 09:01pm | #10

            Keep following Jim's "misconceptions" and you'll probably be alright.

            I didn't miss the sarcasm in his post - just took the opportunity to fullfill some of my IDP required hours. I need 8 more "know it all" credits before they will let me take the exam. :-)>Kevin Halliburton

            "I believe that architecture is a pragmatic art. To become art it must be built on a foundation of necessity."  - I.M. Pei -

          5. jimblodgett | Dec 04, 2003 10:02pm | #11

            I wasn't being sarcastic.  Sorry if it reads that way.

          6. User avater
            GoldenWreckedAngle | Dec 04, 2003 10:12pm | #12

            Sorry, I just read your stating the facts as misconceptions with a smirk. Thought you were trying to be a funny guy.Kevin Halliburton

            "I believe that architecture is a pragmatic art. To become art it must be built on a foundation of necessity."  - I.M. Pei -

          7. andybuildz | Dec 05, 2003 12:47am | #16

            All of a sudden I spell plywood...ADVANTECH....I'm totally sold!

            Be rock solid and PL Premium and screwed (in a good way ; )

                                                  andyMy life is my practice!

            http://CLIFFORDRENOVATIONS.COM

      2. joeh | Dec 04, 2003 07:55pm | #8

        Jim, I think the C stands for crap. D is for double, as in "Crap both sides"

        X is for EXPENSIVE.

        Joe H

      3. User avater
        GoldenWreckedAngle | Dec 04, 2003 11:37pm | #13

        I sent an e-mail to the APA for the real skinny. Wow, I'm with Jim - love the stuff I learn here!

        My question:

         -----Original Message-----From: Kevin HalliburtonSent: Thursday, December 04, 2003 11:45 AMTo: HelpSubject: Plywood glue

        I just read the following statement, from a very knowlegable builder, on a building forum I frequent:

         

        "To the best of my knowledge, at least here in the West, all plywood has been layed up with exterior glue since the late 60's to early 70's.  (Doug Fir ply, anyway)"

         

        Is this true? If so, what is the manufacturing distinction between APA "exposure 1" and "interior" designations on plywood?

         

        APA's response:

         

        The statement is true.  Construction plywood is only manufactured in Exterior and Exposure 1.  I am not aware of anyone producing interior grade construction plywood to the PS1-95 standard.

         

        For PS1-95 plywood the difference is that Exposure 1 plywood allows D Grade veneers.  Exterior plywood allows for a minimum C Grade veneer.  Compositional factors such as the D Grade veneer have an effect on the exposure durability classification.  Both types of plywood are manufactured with the same type adhesive.

         

        C-D Exposure 1 (CDX) plywood sheathing is the typical Exposure 1 plywood.

         

        I hope this information will be of assistance to you.  Please let us know if we can supply you with further information.

        Regards, Ray Clark Product Support Specialist Wood Products Support Help Desk APA - The Engineered Wood Association Southern Forest Products Association

        E-mail: [email protected] Tel:    253-620-7400 Fax:    253-565-7265

        Web Sites: http://www.APAwood.org http://www.SouthernPine.com http://www.SFPA.org Kevin Halliburton

        "I believe that architecture is a pragmatic art. To become art it must be built on a foundation of necessity."  - I.M. Pei -

        1. Jeff | Dec 05, 2003 12:45am | #15

          Hi all

          Thanks for the answers, makes me feel good to know this forum exists.

          Jeff

      4. FrankB89 | Dec 05, 2003 05:31am | #17

        My post was hurried 'cause I was on my way out the door, but....I'm glad to see that better minds than I got verification.  One of the BAD things on this forum is to throw out wrong information and then suffer getting climbed on!  :-)

        My Father worked in a plywood mill for some 25 years and I worked in the same plant for a short time.  I do remember when there were interior and exterior glues used.  In the Weyerhaeuser plant where he worked, I believe the glue used for interior was blood based.  Cattle blood from slaughter houses was a common bulk glue additive for plywood manufacture (I can still recall that "blood" smell in his clothes when he'd come home at night).  Exterior glue was akin to a resorcinol formulation and more expensive.

        Chemical research eventually succeeded in developing a glue formulation that, thankfully, made the blood glue obsolete, and in the process, made the use of exterior glues cost effective across the board.  (And Dad began to smell better!). 

        1. jimblodgett | Dec 05, 2003 07:33am | #18

          Thanks, Notcher.  I would probably have gone to my grave thinking that dated stuff about plywood and glues.

          So much to learn, so little life.

          (came back to say) and thanks to you too Kevin, for tracking down that info from APA, very helpful.  The gal who oversees their website is married to my best old carpenter buddy - they and their kids spend Thanksgiving here with us most years, we went to their wedding, they went to ours...one of life's treasures, old friends.

          Edited 12/4/2003 11:38:29 PM ET by jim blodgett

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