8

Lots of plywood at Home Depot have the letters RTD in the title, with no further detail. Many of these have multiple user questions of the form "What does RTD mean?" Answers seem to be split 50/50 between what it actually means though. On the one hand are those who think RTD stands for the manufacturing process. Almost all of these answers (and others on the internet) seem suspiciously close to this wording on theplywood.com which makes me suspect that a single source from 2017 has been repeated over and over on the internet enough times that it's being accepted as infallible.

Example:

RTD refers to the method used to manufacture the plywood. This is, essentially, next generation CDX plywood which is manufactured with a quality control system using RTDs (Resistance Temperature Detectors) to maintain correct temperature during the bonding process. This process helps ensure complete bonding of the layers to minimize delamination.

On the other hand are those who think RTD just means it's "rated," here's an example:

RTD is an abbreviation for RaTeD. Yes in the manufacture of plywood the use of Resistance Temperature Detectors is normal to ensure delamination does not occur later on. But this generally applies to all plywood manufacturing, not just to those listed as RTD.

So which is it?

brentonstrine
  • 970
  • 3
  • 14
  • 27
  • Both of your definition states it is a process. I do not understand how you derived the second definition as a rating. Both of your definition, it states it is a process. So RTD states that the manufacturing process used RTD. – Programmer66 Apr 28 '20 at 04:57
  • @progrmer66 I think you are missing the "Yes, but" form of the answer. It is acknowledging that RTD is also a manufacturing process but explaining why that is not what it means in this context. – brentonstrine Apr 28 '20 at 11:12
  • Most plywood the only difference is the grade of the veneer And the core. I worked In a large mill and that was the only difference I ever saw , the detectors that look for voids or “blows” only use different settings for different thickness. MDO & HDO are the highest level and hand laid with the best veneer but the same glue is used, the same pre press and hot press process the only changes are based on thickness well and hdo has a special paper laminate on the outside. There are other things like plugging , sanding and patched. But these just hide the defects. If there are no blows they pass – Ed Beal Apr 28 '20 at 17:32

3 Answers3

2

The “RTD” in RTD plywood stands for Resistance Temperature Detector.

You have your normal CDX plywood for exterior sheathing. This plywood is made to function better outdoors - deals with temp changes and moisture better than other forms of plywood. The main difference between this and your normal plywood is that you will have less delamination.

Now RTD takes the CDX a step further and has controls for the amount of glue used, types of glue, and most importantly making sure the bonding temperature is highly accurate for each layer of veneer.

This will result in less delamination for CDX and makes it superior for outdoor use.

The grading difference between the two most common types of plywood can be summed up in that CDX is Exposure 1 rated (which means that water hitting it won't hurt it) and RDT is purely Exterior rated (yes I know CDX is still used as exterior sheathing in some places). Being exterior rated means it will withstand constant exposure to temp changes and moisture.

Depending on the price difference we may buy CDX for subfloors but RDT is used for everything on exterior, including walls and roof.

DMoore
  • 47,296
  • 15
  • 79
  • 187
  • >"RTD is purely Exterior rated." Here is an RTD plywood for interior use (look at the specifications under "Weather Exposure." https://www.homedepot.com/p/23-32-in-x-4-ft-x-8-ft-RTD-Sheathing-Syp-157946/100041308 – brentonstrine Apr 28 '20 at 11:04
  • What would you say to those, like the second commenter I quoted, who say that _all_ plywood these days uses the RTD manufacturing process, so it would be a meaningless distinction. – brentonstrine Apr 28 '20 at 11:10
  • @brentonstrine - Exterior rated means it can hold up to standing water and vast changes in temperature. It does not mean it can't be used for interior use. I even mentioned we "may" buy CDX for subfloors - which means if the RDT is close in price we will use that. Graded for exterior use does not mean you cannot use it for interior. – DMoore Apr 28 '20 at 16:40
  • 2
    @brentonstrine - that isn't true. If a manufacturer went through the RTD process and spent all of that money they could surely spend an extra half penny per board to stamp it. The fact that someone says that means that they probably only shop at big boxes that only carry RTD. – DMoore Apr 28 '20 at 16:42
1

This might give you an appreciation for the difference:

Below is a basic old fashioned plywood press machine, the kind that has been in use since plywood was invented. Stack a bunch of layers of veneer on top of each other, some with glue between them, ever so often no glue, which differentiates the individual sheets. Then you press them together with a 400 ton hydraulic press and wait for the glue to set. You know an AVERAGE amount of time it takes under pressure, but to make SURE, you add more time just in case. enter image description here

In a more modern system, the glued and unglued veneer sheets are fed in between plates of steel before being pressed by the hydraulic rams. enter image description here

Those plates have small tubes carrying steam though them to heat the product as it is being pressed and buried in those plates are RTDs, Resistance Thermal Detectors, that tell the computer exactly how hot the plywood got. This way the computer KNOWS when the glue is set, so it eliminates the guess work and cuts the cycle time to make each batch. It's a more expensive process, but results in a more consistent product quality and a higher production volume, resulting in more economies of scale and thereby, lower costs.

JRaef
  • 14,724
  • 1
  • 17
  • 39
  • This is fascinating and a great answer to the question "what is the difference between RTD and non-RTD plywood" which is, unfortunately, not the question I asked. Since you seem knowledgeable, I wonder if you can shed insight on whether most all plywood at big box stores is made with the RTD process? – brentonstrine Apr 29 '20 at 23:43
  • Well, I felt that the "what does RTD mean" question had already been answered, it means Resistive Thermal Detector" (or Device), not "RaTeD". Rated is generally abbreviated Rtd, not RTD, if it is abbreviated at all (you would only be "saving" two letters...). So I was providing info on what makes them different. Plywood made using the RTD method ends up as higher quality with more consistent product quality, leading to higher yields in production and explains why although it is "better", it is lower cost. Lower costs and fewer returns generally appeal most to "big box stores". – JRaef May 01 '20 at 19:30
0

But to confuse things even more, there are devices used to measure temperature in demanding applications that are called Resistance Temperature Detectors, or RTDs. These devices see a lot of use in space applications, where they have been used since the early days of the space program in the 1960's.

Goodrich Aerospace is one of the manufacturers of such devices.

Not anything to do with plywood .

SteveSh
  • 6,076
  • 1
  • 8
  • 25