# Forum Contacts & Links Timber, Tools & Hardware Suppliers  Difference between Ply grades

## nev25

I'm wondering what the difference is between marine ply and structural ply and normal ply (if there is such a thing) 
I'M told the marine ply they use a a waterproof glue 
Is this right 
Also the different grades
I use to manufacture Speaker boxed which I used CD grade and was told CD meant one good side???
Someone elaborate??

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## journeyman Mick

Nev,
exterior ply and marine ply both use the same glue which is good for 48 hours in boiling water according to the standard. the difference is in the make up of the plies, with marine grade having more and finer veneers and not allowed any voids. Structural is not waterproof. 
Mick

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## snowyskiesau

*Got this plywood  info from timber.org.au*  *Veneer quality* 
  There are 5 veneer qualities specified for plywood in the Australian Standard The veneer quality relates to appearance only, and not to structural properties.   *Veneer Quality A*: is a high appearance grade veneer suitable for clear finishing where surface decorative appearance is a primary consideration.*Veneer Quality S*: is an appearance grade veneer that permits natural characteristics such as knots as a decorative feature. The type and frequency and type of characteristics permitted is part of a written specification acceptable to both manufacturer and consumer.*Veneer Quality B*: is an appearance grade suitable for high quality paint finishing.*Veneer Quality C*: is a non-appearance grade with a solid surface (all open defects are filled) and is designed specifically for applications requiring a solid non-decorative surface such as flooring which will be overlaid with a decorative flooring surface.*Veneer Quality D*: is a non-appearance grade with open imperfections up to 75mm wide, and is designed for applications such as structural plywood bracing. 
  Structural plywood is manufactured in accordance with This Standard provides for plywood to be graded according to veneer quality and stress grade. 
  Plywood is specified by both faces, two letters; the first being the face veneer quality and the second the back veneer quality. This allows some economy as one face of a plywood sheet is often hidden from view and a lower grade face can be specified for the non visible face. For example, AD calls up a plywood with the front face A grade and the rear face D grade.  Plywood flooring is typically specified as CD.
  Other examples;
  AA for marine plywood,
  AD for wall cladding where only the front face is visible,
  CD for structural plywood flooring
  DD for hidden structural bracing 
  It should be noted that a plywood with D faces is not necessarily structurally inferior to one with A faces as the terms relate to aesthetic quality. The structural attributes of the plywood are allocated via a stress grade.

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