RTD plywood is the next generation of plywood made specifically for the construction industry. As with WBP plywood, the letters R, T and D do not refer to the grade of plywood, but rather to an important part of the manufacturing process. Specifically, it refers to plywood that has been manufactured using a Resistance Temperature Detector. This is a device used during the manufacturing process that provides a highly accurate reading of the temperatures achieved during the bonding process.
It has long been known that the bonding process is both the strength and weakness of plywood products. It is the strength, in the sense that what makes plywood strong is the multiple layers or veneers being bonded together, with adjacent layers laid perpendicular to each other. But at the same time, it is the weakness because of limitations in the adhesives used in the bonding process.
While these adhesives or rosins are often stronger than the wood fibers they are bonding together, they have their limitations, especially when exposed to moisture. In many cases where plywood fails, it is because of delaminating. That can only happen when the adhesive either dissolves or loses its strength.
The first major effort in solving this problem was with WBP plywood. This acronym stands for “water and boil proof.” Plywood which is rated as WBP has been tested to verify that it can stay bonded together in boiling water. In order to make the plywood do that, it is made with melamine or phenolic resin.
RTD Plywood takes the improvement that WBP plywood gives a step further. It was discovered that improving the accuracy of temperature control during the bonding process led to a stronger bond. This required developing the means of reading the temperature in real time. Plywood which has been manufactured following this new process is stronger and is more resistant to moisture damage than plywood manufactured before. Ultimately, this means that the RTD Plywood is less likely to experience delamination than other CDX Plywood that is manufactured without the use of a resistance temperature detector in the laminating process.
This reduces problems in the home-building process, especially problems caused by exposure to moisture. But it can also help guarantee that homeowners will have less reason to call the builders at a later time, about problems with their home. By ensuring a solid bond between layers, there is less likelihood subfloors delaminating, causing squeaks and other noises in the floor.
In order to fully understand how RTD plywood compares to the CDX plywood which has commonly been used by the construction industry up until this time, we need to understand exactly what that CDX plywood is and how it is graded.
When someone goes to purchase plywood they will often see letter designations concerning the grade of the product. Such as the CDX plywood which is commonly used in construction. The grading system used for softwood plywood that is used in construction is done with the letters N, A, B, C, and D. These grades are based upon the quality for one side of the plywood. It refers to the number and size of the defects allowed.
Each side of a sheet of plywood is graded separately, although they are noted together. CD plywood refers to plywood which meets the requirements for grade C on one side and grade D on the other. Most plywood will have one side which is graded better than the other. This better side is referred to as the “face side” and the other side is called the “reverse side.”
In this grading system, N is the highest grade with the fewest possible defects and D is the lowest grade with the most allowable defects. For example, grade N plywood will be sanded very well and the blemishes will be practically nonexistent. Grade D plywood, on the other hand, will have the maximum allowable blemishes, such as knots. A-A grade plywood is sanded with minimal defects on both surfaces. This type of plywood is often used on interiors, such as kitchen counters. On the other hand, C-D grade plywood is what would be used in construction projects for the exterior walls of buildings. This would later be covered with siding.
How is Plywood Made?
So know that we know how plywood is graded, how is it made? Plywood is made by gluing together thin layers of wood veneer. In cases other than hardwood plywood which is used for furniture and cabinetry, this veneer is peeled off of a log in one continuous sheet, rather than sawn like boards are. However, hardwood plywood often uses sawn veneer for the face layers.
Prior to the layers of wood veneer being bonded together, they are soaked for up to 40 hours. This is done in order to soften the wood, which makes the pressing process go much smoother. Various sheets of veneer must often be laid together, butting up against each other to eliminate or minimize gaps. In order to increase strength and minimize shrinkage, each layer is laid perpendicular to the previous layer.
All plywood has a minimum of three veneers, although more is preferable, especially as the plywood gets thicker. The more veneers in a piece of plywood, the stronger it will be. These layers, along with the glue, are heated and pressed together to form a tight bond. The type of glue used is what actually dictates what the plywood will be used for.
The X in CDX plywood, commonly used for construction, refers to the type of glue that is used in the manufacturing process. In this case, the X stands for exposure, although many mistakenly think of this as referring to exterior. However, while exposure graded plywood is designed to be used on the exterior of a home, the defining factor is that the glue used in the manufacture of this plywood is selected to permit the plywood to withstand exposure to the elements, without delaminating.
However, exposure grade plywood is not waterproof in the sense that pressure-treated plywood is. Rather, it is much more moisture resistant than non-exposure grades of plywood. Exposure grade glue is used, in the expectation that there might be rain or snow during the construction process. This plywood should only be exposed to moisture for a short period of time.
CDX plywood is referred to as Exposure 1 plywood due to the quality of glue utilized for bonding. Examples of its uses include, but are not limited to, tile underlay, walls, and roof sheathing. If it were to rain during the construction of a building, this CDX Plywood would be able to stand against the elements for a short period of time. However, it is not recommended for use in areas of high humidity or moisture.
If a construction project is taking place in an area of high humidity, or the project will be exposed to moisture for long periods of time, it is recommended to use Marine plywood. The design and structure of this plywood makes it resistant to fungal damage and delamination caused by excessive moisture.
CDX or RTD
Early it was mentioned that RTD plywood is the next generation of CDX plywood. But how is RTD plywood similar to and better than CDX Plywood? RTD Plywood is better because of the way it is created in a manner that helps to prevent delamination. This is most commonly caused by the use of too little or too much glue during the manufacturing process. It can also be caused if the layers of wood and glue were not heated to the proper temperature during the pressing process. RTD plywood is the answer to these issues.
RTD and CDX plywood are essentially the same exposure 1 graded plywood, except for the superior manufacturing quality of the RTD plywood. This higher quality in the manufacturing process is what makes the RTD plywood a superior product to its CDX predecessor. This doesn’t mean that CDX plywood is faulty or bad, it simply means that RTD is a bit better as a final product.