The premium grade plastic lumber has the nicest finish, and is the usual choice
when there is any milling required. It is also the best choice for decking
since it is available in tongue and groove and many other stock sizes
The molded and landscape grade
plastic lumber are still made with high density polyethylene
just with a different extrusion method, the end result being a denser
board, a little rougher grain, and truer dimensions. This method also
limits length availability, and you are more likely to find "voids",
though usually small.
The structural grade plastic
lumber has the same attributes as described above for
the molded and landscape grades, with one major difference. We
add chopped fiberglass to the polyethylene that makes the lumber approximately
4 times stiffer than the other grades. These boards are the choice when free spans beyond the capability
of the other grades are required. It is most commonly used in
understructure in deck construction, though there are many other applications
such as pergolas and arbors. This grade, because of the heavier
fiberglass additive is also the heaviest grade on a size by size comparison
with the other grades.
The industrial grade lumber is again high density polyethylene and although
behaves like the premium grade does, the texture and shape consistency
is not as good. This grade is used where utility and price are
more important. Typical uses are shipping pallets, industrial flooring
and shelves, truck beds, crating etc.