I heard that the "C" and "D" stood for the grades of each side, as mentioned
above, but the "X" meant that an eXterior grade adhesive was used in the
plywood.
--
Calvin Henry-Cotnam
"Never ascribe to malice what can equally be explained by incompetence."
- Napoleon
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Nope, that is what I said to him. He said there are plenty of exterior glue
grades of plywood that don't say "X". It is just that this is "sheathing grade"
and does not need the surface hardness you get when the next layer of wood is
plugged (knot holes). He says in an underlayment application CDX will fail if
you put a chair leg over the void and you will have a dimple.
The way I understand it is that the "X" in "CDX" means exterior glue,
but not exterior exposure. IOW, CDX can be used in places with high
moisture content, but it cannot be permanently exposed to the weather.
"Exterior", on the other hand, does mean that the plywood can be
exposed to the weather. For example, "AB Exterior" is what we often
use for soffit replacement since it can withstand long-term exterior
weather exposure.
Both sides of CDX look pretty bad but we always install the side with
the stamp facing down. We do this because the permit department wants
to be able to see the type of decking we used if they go into the
attic. The problem is that the stamped side is the rougher "D" side
which makes a better walking surface when installing the roof than the
somewhat smoother "C" side.
As far as I know, the stamped side is always going to be on the worse
side since the better side will be the one exposed.
Bruce
A&B Construction
Houston, TX
www.1-866-roof-men.com