Plywood is a common wood sumproduct that consists of glued wood veneers. There are different types of plywood in the market, and we can identify if it is made with softwood, or hardwood, or if it is mixed. Because of that, each different application requests a different plywood. So, to identify each plywood is ideal for each application, we have a plywood quality grading. It is a method to classify the visual and structural characteristics of each veneer.
In this text, we will talk about the pine plywood classification, which is a softwood. Firstly, to understand better, the process of production of plywood passes by many steps of classification, starting with wood selection, in the woodyard. The second moment is after the lamination of wood, here the veneer with fewer knots goes to a “surface” of plywood. The third classification is after pressing the plywood sheets, where we have the final product that is ready, in this step happens the plywood quality classification.
Pine Plywood common quality grading in Brazil
In the final stages of the production process, the plywood classification follows some criteria that differentiate each product, according to its final application. To have an easier identification, worldwide it used the letters A to D, where A is plywood with better quality and D is lower quality.
Here in Brazil, we have the PNQM, a national program for wood quality that helps industries to identify the plywood quality grading. This ranking analyzes the plywood surfaces and it uses two letters. The first letter identifies the face, and the second letter the back surface.
See below what are the differences between each plywood classification:
- “A”: the highest quality, in “A” veneer we don’t have knots or color variation. It will be more expensive and are usually used in projects that will be visible to the eye. This type of plywood is smooth and easy to paint.
- “B”: In B grade, there is a change in appearance color, wood grain pattern. It will generally have smooth knots, but is free of open knots plugs. It is slightly less smooth than “A” plywood classification.
- “C”: In this plywood quality grading, we have more visible flaws and knots. Use “C” plywood where you need strength, like construction purposes. In C Grade material it is possible to see discolouration, splits, defects and open knots on its surface. This plywood is not recommended to use in places where the appearance is necessary.
- “D”: The letter D, in plywood classification, has large flaws and knots. This is typically the cheapest grade of plywood veneer.
To understand better, see this table below:
Plywood classification table
| TYPE OF DEFECT | FACE VENNER GRADE | ||||
| A | B | C+ | C | D | |
| SOUND KNOTS | Not accepted | Less than 10mm in diameter and maximum 10 units/face is allowed | No limitation. | ||
| OPEN KNOT/OPENINGS | Not accepted | Open Knots and openings caused by machinery instruments not bigger than 6 x 12,5 mm and repaired with filler. | No limits for open knots and holes caused by machinery instruments. However its sizes shall not exceed 65mm in diameter with average under 50mm and repaired with filler. | No limitation. | |
| CORE GAP | Gaps under 20mm are allowed | Gaps under 50 mm are allowed | No limitation. | ||
| OPEN JOINTS | Not accepted | Open joints not larger than 2mm in width and repaired with filler | Open joints not larger than 5mm in width and repaired with filler | No limitation. | |
| CRACKS | Not accepted | Cracks less than 5mm in width and 300mm in length, and repaired with filler | Cracks less than 10mm in width and 600mm in length, and repaired with filler | Cracks less than 15mm in width and 700mm in length, and repaired with filler | No limitation. |
| NUMBER OF FACE JOINTS | None | Only one | Up to two | Up to four | |
| LAP | Not allowed | One per m2 not exceeding 100 mm in length | Up to two per m2 not exceeding 400mm in length | Up to two per m2 not exceeding 600mm in length | No limitation. |
| BLUE STAIN | Not allowed | Up to 10% of faces area | Up to 20% of faces area | No limitation. | |
| WOOD REPAIR/PATCHING | Not exceeding 25 mm in width and 200 mm in length, combined in color and grain, glued with same resing of the panel production | Not exceeding 100 mm in width and 600 mm in length, combined in color and grain, glued with same resing of the panel production | Not exceeding 25mm in width and 700 mm in length, combined in color and grain, glued with same resing of the panel production | No limitation. However glued with the same resin of the panel production. | |
| SUM OF FACE DEFECTS (OPENED JOINTS + CRACKS + WOOD REPAIR/PATCHING + OPEN KNOT) | The number of repair shall not exceed 6 of the total panel surface | The number of repair shall not exceed 8 of the total panel surface | The number of repair shall not exceed 30 of the total panel surface | No limitation | |
Source: PNQM – Pine Plywood technical Catalogue – #1
Examples of applications
With all these criteria of plywood classification, many types of plywood can be formed. And each combination of face or back veneers is ideal for an application: for structural ones, or floor, or furniture… So, what is the ideal match for my purpose? Let’s see some examples of applications and what are the plywood quality grading to anyone:
- Concrete formworks – To make a good form, the plywood needs to be sanded, to guarantee a beautiful finish in appearance concrete. It most commonly uses “BB” plywood classification.
- Furniture – To destiny a plywood to furniture, before we need to analyze what will be the appearance, if it will be painted or not. For painted furniture, uses “BC” plywood quality grading, and in not painted furniture usually uses “AC” classification.
- Floor decking – the plywood classification to floor or decking is “CC”, because commonly receives a second coverage, and it doesnt request a good plywood appearance, without knots, for example.
- Wall Sheathing – This plywood could have some knots up to 60 mm in the face and up to 75mm in the back. Because of that, it commonly uses C+C plywood quality grading.
- Packing – to packing purpose, plywood classification is C+C. Because it needs some structural highness, but the appearance is not important here.
There are many more types of plywood, and you can find the best for your application by talking with a specialist or a producer. Is important to know that many countries produce plywood and each one has a different plywood classification. So, before buying plywood, get some information of local plywood quality grading and you can make the best plan for your project. Here in Brazil, you could find this information on the ABNT site.
