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Plywood and OSB are two of the most popular engineered wood products.
They were used as sheathing for walls, floors and roofs in homes in the 70s and 80s, but nowadays,
they are mainly used for custom homes. These two products were developed for the same
reason; to replace solid wood, which is getting expensive and scarce. They are made of cheap,
fast-growing and inferior softwoods but they perform just as well, if not better than solid
hardwoods. Why? For 2 reasons, the resins and glue embedded inside and the orientation of
the wood pieces. In this video, we’re going to look at how plywood and OSB are made, their main
differences as well as their pros and cons. Let’s start with plywood. As the name suggests,
it is made of thin layers or plies of wood veneer. Tree trunks are placed on a conveyor belt and sent
to debarkers. The machine removes the bark of the tree either with sharp-toothed grinding wheels
or with jets of high-pressure water. To soften the wood, the logs are heated and soaked in hot
water for over 12 hours. A lathe rotates the log while a knife peels a continuous sheet of veneer
eight of an inch thick. The ribbons are cut into 4 by 8 sheets and dried at 400F. Veneers are run
through a glue curtain which coats all the sheets except the top most sheet. The veneers are layered
crossgrain and put through a heavy press. This heats up the glue and binds the sheets together.
Finally, the boards are cut to size. Plywood is so strong because of cross-graining.
The grain on the top and bottom surface run lengthwise while the layers beneath
them run at 90 degrees. Regular, solid wood grain runs in the same direction,
so a split can spread through the whole board. Cross-graining prevents splits in plywood when
nailed at the edges. It also reduces expansion and shrinkage and improves stability. Cross graining
is also why plywood has an odd number of layers; 3 ply, 5 ply and multiply for 7 or more layers.
Plywood is also graded from A to D, based on the quality and appearance of the top and bottom
veneers. The best plywood is used for furniture. The worst can be used for sheathing.
Now let’s look at how OSB or Oriented Strand Board is made.
As the name suggests, it is made of strands of wood oriented in different directions.
Trees are debarked then placed on a machine called a strander. This has a set of knives that cut the
trees into strands of wood with a specific width, thickness and length. The strands are then dried
to reduce the moisture content. After drying, the strands are filtered out into different sizes
and blended in a rotating drum with resins and wax. Long strands on the top and bottom
face one way, while the short interior strands face the opposite direction.
Eight inch thick mats are pressed at 600 psi while heat cures the resin. OSB boards roll
off the press and are allowed to cool down before being cut to the correct length and width.
OSB is a consistent product because there are no gaps or overlapping knot holes.
It is strong because the wood strands are arranged in cross-oriented layers.
In fact, the shear value of OSB is 2 times greater than that of plywood. There are
4 main types of OSB. The best is used for i beams, subfloors and roofs, the worst is used
for packing and furniture. The most common glue used in plywood and OSB is phenol formaldehyde
or phenolic resin. Under heat and pressure, the resin infiltrates the wood cell wall and bonds
with wood cell wall polymers like lignin. Before we discuss the properties and pros and cons
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Now let’s look at the properties of plywood and OSB. Plywood is a very versatile product that
can be found in different thicknesses from eighth of an inch to 3 inches. It can be made of several
different wood products. This Maple plywood from Home Depot has 2 veneers of maple wood
on the top and bottom, but the 5 infill layers are made of cheaper wood like poplar or fir.
Softwood plywood is used for floors, roofs and walls Hardwood plywood is used for
furniture and cabinets. Marine plywood is used for boats and piano cases. Pressure
treated plywood is used for garden sheds. OSB has a rougher appearance and surface texture.
It can be found in thicknesses from quarter of an inch to over 1 inch. Because it’s made
of wood chips, it doesn’t have the same size constraints as plywood. You can find much larger
panels of OSB. It is made of fast-growing pine and poplar wood. OSB is mainly used for sheathing,
floors, and joist, places where it is hidden. Some people try to make furniture out of it by coating
the surfaces in a thick layer of resin. Plywood seems to leave behind less sawdust when
cut. Cutting OSB is messier and the edges are more prone to splintering. Both plywood and
OSB hold nails and screws in place. When screws are removed, they may damage the
strands of wood in OSB but it all depends on the quality and grade of the product you use.
Now for the cost. It’s tough to discuss this because of the crazy prices we’ve seen over
the past 2 years. A 4 by 8 ft sheet of plywood sheathing used to cost $25 is now $46 at Home
Depot. A 4x8 ft sheet of 7/16 inch OSB used to cost less than $10, but now costs $46 at Home
Depot. There are many possible reasons for the spike in prices. One is the freeze in Texas last
year. The chemical plants that produce resins and binders shut down for several weeks,
which caused a shortage of raw materials. I made a video on lumber prices last year, I’ll
link it up here if you want to check it out. Plywood generally has better water resistance and
dries out more easily but it is not waterproof. Prolonged exposure to moisture will cause rot. OSB
has a reputation of performing poorly when exposed to moisture. The edges of this board swelled
and it didn’t dry out as fast. However, OSB is constantly being improved. Advantech, which is
a premium OSB product, is water resistant because of its density and higher amount of resin.
If these engineered wood products are used inside homes, the chemical binder can affect our health.
Most plywood manufacturers use urea formaldehyde glue which can off-gas. When I buy wood to make
furniture, I only buy PureBond plywood at Home Depot which uses a non-toxic, soy-based binder.
It’s the same glue that’s used in HempWood, another video for you to check out later.
OSB can use melamine fortified Urea Formaldehyde,
Phenol formaldehyde and polymeric methylene diphenyl diisocyanate.
These are moisture resistant binders, but they off-gas VOCs or volatile organic compounds.
This piece PureBond plywood charred, but didn’t catch on fire. OSB charred more easily
and gave off strong fumes. Some OSB beams burn 8 times faster than solid wood beams. However,
you can find fire resistant plywood and OSB that perform very well when exposed to flames.
Finally, environmental concerns. They are both excellent man made or engineered wood products.
They allow us to use lower quality wood, fast-growing.
OSB is generally considered to be more sustainable because you can use wood chips instead of
a whole sheet. Nothing goes to waste. In conclusion, both plywood and OSB are incredible
inventions that have allowed us to use wood in a smarter manner. We have “tamed” nature by turning
trees into panelized, modular products. They are both versatile products that have fairly good
water and fire resistance. OSB is a newer product and I think it has a lot of potential and is going
to keep improving. Plywood is excellent for DIY furniture projects. I’ve built a dresser, TV stand
and some tables with this Maple plywood. I’ll post the photos of those projects on my Instagram page.
Also, let me know if you enjoy these comparison videos because I really love making them.
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