Plywood is one of the most commonly used types of engineered wood. It is often used as an alternative to solid wood for furniture making and construction.
It comes in many types and grades, depending on quality, strength and durability.
RTD and CDX are the two most popular types of exterior grade, i.e. plywood that can be used in outdoor projects and can withstand exposure to moisture and other natural elements.
If your woodworker is asking you to use RTD or CDX plywood in your exterior project, it might help to know about these two types of plywood along with their respective properties, pros and cons, and the differences between RTD and CDX.
RTD vs CDX Plywood : Overview
| Characteristic | RTD | CDX |
|---|---|---|
| Material Composition | It is typically made from hardwood or softwood veneers, with an emphasis on high-quality face and core veneers. | CDX is made from softwood veneers with a C-grade front face and a D-grade back face. |
| Surface Quality | Features a smooth and sanded A-grade face veneer with fewer imperfections. | It has a rougher, lower-quality face veneer with more knots and imperfections. |
| Application | RTD plywood is often used for fine carpentry and woodworking projects where appearance and finish quality are important. | It is commonly used for structural and sheathing purposes where appearance is less critical, such as roofing, subflooring, and exterior wall sheathing. |
| Price | It tends to be more expensive due to its higher quality and better surface finish. | It is usually more budget-friendly because it is designed for structural applications. |
| Thickness Options | Available in various thicknesses, depending on the manufacturer’s specifications. | Typically available in standard thicknesses, such as 1/2 inch and 3/4 inch. |
RTD (Resistance Temperature Detector) plywood offers superior resistance to water and temperature. It is an extremely durable with greater stability compared to CDX, making it a superior choice for use in applications with extended exposure to moisture and harsh weather conditions.
The key difference between the two lies in their manufacturing methods. RTD is meticulously produced under strict conditions of quality control, where Temperature Detectors are used to ensure precise temperature parameters during the bonding of layers of plywood. On the other hand, CDX is formed through a regular plywood making process, which involves glueing and pressing together wood veneers.
Both plywoods are constructed using high-quality veneers and water-resistant adhesives, which make both types suitable for outdoor use. Since these plywoods are normally unfinished, they are generally favoured for applications where strength and durability are more important than appearance, such as building structures.
What is CDX Plywood?
The word CDX is made from three letters, C, D, and X, where C or the first letter refers to the front side of the plywood.
As you may know, plywoods are rated between A to D based on quality, where A-grade indicates the best quality with the fewest decades. C-grade is better than D-grade.
The letter D in CDX represents the backside of the plywood, which is slightly inferior to the front C side. The letter X indicates the type of adhesive used in the construction. In this case, it means exposure (X=Exposure), which shows that the it can withstand exposure to moisture. However, it’s not waterproof and should not be continuously exposed to bad weather.
Pros & Cons
The top advantages of CDX plywood include high strength and durability, resistance to moisture, easy accessibility, affordability, and versatile uses. It is lighter than solid wood and is a sustainable wood choice.
There are some disadvantages of using CDX, which include the average appearance due to unfinished plywood (not suitable for interior applications), not resistant to insects, not suitable for excessive humidity conditions, and prone to layer separation.
What is RTD Plywood?
Resistance Temperature Detector (RTD) plywood is a specially engineered wood product that is commonly used for wall and roof sheathing for its outstanding resistance to moisture and weather elements.
It is often regarded as a stronger and more durable version of CDX plywood and is particularly well-suited for outdoor applications, such as roofs, where it might be exposed to harsh weather.
Unlike conventional plywood types, the letters ‘RTD’ do not denote the plywood grade; rather, they stand for ‘Resistance Temperature Detector,’ and refer to the process through which this plywood is manufactured. This detector is used to continuously monitor temperature levels during the bonding process of layers during the construction of RTD plywood. Temperature monitoring helps ensure superior bonding between layers, which results in a strong and durable plywood that is free from issues like delamination.
Pros & Cons
The main advantages of using RTD plywood include ease of workability, great resistance to moisture and weather, extreme durability and stability, and less prone to decay over time.
The disadvantages include heavy weight, more expensive than CDX, low availability, and unfinished appearance.
RTD vs CDX Plywood: How to choose?
If you, like many other people out there, are wondering whether to opt for RTD or CDX plywood for your next exterior project, here’s everything you need to make a decision.
While this choice may not have a one-size-fits-all answer, most woodworkers favour RTD over CDX, especially for exterior sheathing and other outdoor applications for the simple reason that it is stronger and better resistant to moisture.
CDX plywood remains an excellent choice for general applications, including construction. Many woodworkers use it for structural applications like subflooring in home construction.
However, RTD is definitely a superior choice in terms of durability for exterior applications. One notable advantage of RTD plywood lies in its temperature control, which reduces the likelihood of layer separation over time. This helps ensure the longevity and stability of plywood, which remains in good condition for a long time. It is also crucial to find and buy the appropriate type of RTD plywood to get the full benefit of its superiority.
Moisture Resistance
CDX is commonly rated as Exposure 1, which means it can withstand exposure to moisture but not consistently for a long time. This means the plywood can be used in the construction process and for applications like subflooring where it won’t be in constant contact with water. However, it should be avoided from getting too wet.
RTD plywood is completely waterproof and is made to withstand exposure to constant moisture. In other words, it can be used in conditions where the plywood will be completely exposed to moisture, such as roofs and marine applications.
Uses of RTD and CDX Plywood
RTD is often called sheathing plywood or RTD sheathing, as this is primarily engineered for roof sheathing due to its outstanding resistance to consistent moisture and weather fluctuations. While RTD plywood offers many advantages over CDX, it is not nearly as popular, probably because it’s still new and less frequent among woodworkers.
CDX is certainly more popular and accessible than RTD plywood. It finds utility in various applications, including subflooring, outdoor furniture, roof decking, exterior siding, crates or boxes, concrete formwork, and many other structural applications such as stages and platforms.
Where to Buy High-Quality CDX or RTD Plywood Online?
Cameroon Timber Export SARL is your one-stop destination to buy sustainable, FSC-certified timber, hardwood, softwood, plywood, and other wood products online with the convenience of home delivery anywhere in the world. We are a globally recognised timber manufacturer and exporter with clients in 30+ countries. Contact us now to get a free quote.
