Yes, plywood and OSB have stamps on them.  They are there for YOUR protection.  If you are in a lumberyard or home center and the plywood/OSB you are buying does not have a stamp on it, RUN DO NOT WALK to the exit.  Without a stamp, you don't know what you are buying and this is one time big brother is looking out for you.

You will find two kinds of stamps on all plywood and one on OSB.  The one we'll talk about today is found on plywood only.  That is the grade stamp.  Now this DOES NOT have anything to do with the quality of the plywood, it has to do with the veneers.  There are 5 different veneer grades, N-A-B-C-D.  In thirty plus years of being in this business, I've never even seen an "N" grade which stands for "natural" so lets forget about that, and talk about A-B-C&D.  A&B veneers are the veneers you find in sanded plywoods.  You would want to buy this if you want a smooth finish to your project.  Something like a cabinet.  If it has a C or a D veneer, this is used for rough applications like roof or wall sheathing (under your shingles or siding) or it could be the back side of a sanded panel  aka A-C.

Now there is a lot of other stuff on here, but the two that mean the most are the big letters A-B-C-D, that's the grade, and is it "interior" or "exterior".  90% of the plywood you see will be exterior, which means it is made with a type of glue that won't dissolve if it gets wet.  Hence it's called, "exterior glue".

When you're in the store, expect "A's" to cost more then "D's".  Like A-C will be more than C-D.

If any of this is confusing, ask the people at the lumberyard.  (lumberyards have real yards and less than 100 parking spaces)  There will always be someone there that understands construction and can give you the advise to do your project right, the first time.

I hope this helps the next time you're shopping for plywood.

Kent Porter

Porters Building Centers