Plywood is used in a variety of places around our home. It can be found on our roofs, in our walls, floors and cabinets.
Plywood gets its name from the way it is made. Thin layers of veneer thickness wood shaved from spruce and pine are stacked in layers or plies with its grain alternating in different directions. Each layer gets a coating of adhesive and the sheet is pressed until the glue cures then trimmed to size.
Most general use plywood comes in 4×8 sheets and thicknesses from 1/8th of an inch to just over one inch.
Some plywood like floor decking is available in a tongue and groove end and T1 Siding will use a lap joint. Interior plywood normally comes in a but joint with flat ends which is preferred for cabinet making.
Exterior and Interior grade plywood sheets will use different adhesive.
Exterior grade plywood should be used on roofs or in applications where direct contact with water is a possibility.
If you are building a structure that will have direct contact with the ground then you should purchase an exterior grade plywood that is pressure treated.
Although it may seem like a good idea using exterior grade plywood in your bathroom as an underlayment is not necessary.
For bathroom or vinyl tile applications you want to apply a Luan Plywood on top of your decking plywood to protect it. If you are applying ceramic tile you want to use a cement board that is glued and screwed and has its seams sealed with thinset or mortar.
Marine Plywood is another example of a plywood product that can withstand water damage. It is used in boat construction and a 4×8 sheet can cost in the area of $80.
Decorative plywood has been used in the furniture and cabinet making business for some time and reduces the need to use full thickness hardwood in your projects. The most common types of decorative plywood would be Mahogany, Oak, Cherry and Poplar.
Decorative plywood is available in full thickness 3/4 inch thick 4×8 foot sheets and it is also available in a thin 1/8th inch thickness for retrofitting cabinets.
Plywood gets its strength from the type of wood, number of layers and its orientation.
High strength plywood is used in aircraft production and other applications that need extremely high strength.
In our homes the thicknesses we may find
- 3/4 inch plywood for floor decking
- 1/2 inch for roofing and exterior wall sheathing
- 1/4 inch in some cabinet applications or utility use
- 1/8th inch for luan underlayment
The letter rating system for plywood is more relevant to cabinet building and interior applications.
Starting with A as the best grade and D as the lowest grade you can find a number of matches that will allow a cabinet maker to save money and use a good A side to the outside of the cabinet and a B or C side for the interior.
A Grade means it is finish ready with few if any imperfections D means it can have visible knots and damage that may or may not have been fixed with butterfly joinery.
If you will be staining the work you definitely want to start with a A or B at the lowest and if you are painting the item a C is as low as you want to go unless the item is purely for utility and not for looks.
Selecting Your Plywood At The Lumber Yard
If you are purchasing lumber for the frame of your house and need decking, sheathing and roofing then you can purchase your products on a pallet. Normally there is no big need to sort through piles of material to pick the best product but you do want to look for markings on the plywood that state its use.
All framing materials whether they are 2×4 studs or plywood decking must be marked as inspected and tested at the factory. These marks are necessary at time of your home inspection so the inspector can read the thickness and properties of the pieces quickly.
If you are building cabinets for paint or even general use stain applications like a book case or other item you can save money by inspecting each piece and picking ones that have the best visual appearance.
In this way instead of purchasing an A grade or A/C grade you can purchase a B/C grade and with the use of a sander and a little filler have your work look just as good. Remember if you are painting the item it will all be hidden anyway.
If you are purchasing Decorative Hardwood Veneer plywood for cabinet making you can also purchase end tape veneer that comes with a heat activated adhesive to hide the plywood layers.