Originally Posted by Steve Rust
The quality of the pressure treated ply is not as good as marine and has many voids which are to be avoided. Most of what I see is rated CDX. The first two letters refer to the quality of the face veneer and the third stands for exterior glue. I think real marine grade ply is rated by a different standard but the construction grade ABX would be similar. I do not like working with pressure treated lumber, cutting , handling, or sanding
due to the chemicals used though they are safer than in the past.
Hence Marine Ply is designated AA
Many plywood boat builders use ABX ply under the assumption that they are only sacrificing the quality of one face veneer (A for B) in favor of a significant price
difference between AA Marine Ply and ABX.
But ABX Ply also has more voids and checks in the core
veneers, as well as footballs in the face
The glues, however, are the same for both AA Marine and ABX
Every few years the Plywood Rating Assoc. lowers the acceptable standards for AA Marine PLY. (allowing more and larger defects in the plys)
Back in the '60s, it would have been considered sacreligious to have AA Marine Ply with ANY face or core defects or voids (footballs were out of the question)
Marine Ply is also usually stored inside (out of the elements) at lumberyards