Why Depot Maintenance Teams Choose PR-1436-GPT Over Paste Corrosion Inhibitors
The lifecycle of all military and commercial aircraft is defined largely by a continuous series of inspection cycles. In the military, there are a few standard inspection cycles that take place at home station or a designated alternate and generally range from a day or two for an hour postflight (HPO) inspection to a few weeks or even months for phase or isochronal maintenance. All airframes have different maintenance cycles for these, but the concept is the same.
The primary off-station maintenance for military aircraft is depot maintenance, and there are a few major depots across the U.S. that focus on different airframes. For instance, Tinker AFB in Oklahoma City handles the B-1 and B-52 bombers and KC-135 tankers.
Depot is when the aircraft is stripped down and thoroughly inspected, and a lot of time is spent completing compliance technical orders while the aircraft is down, along with delayed and deferred items. It is also where consumables like sprayed-on sealants are often applied since so much of the skin is removed, and so many cavities are open for inspection and repair.
Let’s take a look at PPG PR-1436-GPT, a leading sprayable corrosion-inhibitive coating.
Corrosion Inhibitors in Aircraft Maintenance
Corrosion inhibition (CI) is the linchpin of aircraft maintenance because corrosion is an absolute destroyer of aircraft. Unchecked metal degradation leads to unsafe aircraft and is extremely expensive to correct, even though safety is the primary concern.
CI sealants and compounds create critical barriers against moisture, galvanic corrosion, and environmental degradation that compromise metal structures (basically, the entire aircraft for most aircraft).
There are two common types of CI products that serve different applications within the aircraft maintenance system. Sprayable CIs like PR-1436-GPT are applied during depot because it is the best time to apply that kind of coating to the aircraft, given the areas where complex geometries are exposed during depot-level maintenance.
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Understanding the Two Categories—Sprayable vs. Paste CI Products
Corrosion inhibitors are split into two main groups, each tailored for a specific situation when it comes to depot maintenance and application. The main differences between these two groups come down to their physical properties, how you apply them, and where they are best used. These factors all have a big impact on how well they do the job, how much time and effort they need to put in, and how well they hold up long-term across different situations.
Paste/Mastic Jointing Compounds (CA1000, CA1010, Mastinox D40)
There are older products designed to prevent corrosion on planes that work by basically not hardening; they stay soft all the time. This means they can stretch and move with the plane as it heats or cools without cracking or losing grip.
Because of this, they work great on parts that are always moving, like joints, and where you need to be sure the seal is just right on faying surfaces. This type of product is especially useful on planes made of composite materials and aluminum, which is prone to corrosion. On the downside, though, these products are a lot of hard work to apply, especially if you need to cover a big area. So, it has to be applied by hand with a brush or spatula.
Because of this, you usually use them to provide targeted protection to the parts most at risk of corrosion, rather than trying to cover everything.
Sprayable Corrosion-Inhibitive Sealants (PR-1436-GPT)
A two-part polysulfide sealant, PR-1436-GPT, forms a strong, flexible, rubbery film that affords excellent corrosion protection. Since it is sprayable, you can quickly cover large areas, and you will not risk thin applications as long as you apply it correctly.
It is hard for many people to understand the magnitude of the CIs used in aircraft like the C-5, C-17, and B-52; these aircraft are enormous. Spraying the CI on the aircraft compresses time tables by rapidly increasing application rates and reducing man-hours, as a single technician can cover broad areas in a short time.
Technical Comparison of PR-1436-GPT vs. Paste-Type Corrosion Inhibitors
Okay, so let’s take a look at how PR-1436-GPT compares to paste-type CIs.
Chemistry & Cure Behavior
PPG PR-1436-GPT is a two-part polysulfide coating that cures at room temperature and forms a resilient corrosion-inhibitive barrier. This provides a strong adhesion to common aircraft substrates, namely aluminum, composites, carbon steel, stainless steel, and titanium.
Once mixed, this material transitions from a sprayable, uncured state to a fully elastomeric sealant and reaches functional hardness over time under standard ambient conditions. By contrast, paste-type materials are permanently mastic, non-curing compounds.
These pastes remain flexible and pliable indefinitely and provide corrosion protection and moisture exclusion without undergoing a chemical cure. This makes them suitable for removable or rework-friendly applications.
Temperature Resistance
Temperature resistance is an important variable, and each of these is a little different depending on its intended use profile. These are not necessarily one-for-one swap items; each is formulated for different purposes and functions.
PPG offers other compounds with much higher temperature thresholds (Mastinox D40 withstands nearly 400°F), but these pastes require a much slower application process. Also, the pastes are not intended for use in the same areas as sprayable PR-1436-GPT; the pastes are non-curing, meaning they remain softer, whereas PR-1436-GPT cures to a hard finish. Again, they achieve similar results and perform a similar task (preventing or inhibiting corrosion), but they are not interchangeable.
Always make sure to check out the Technical Data Sheets for each product to make sure you are working with the correct CI.
Temperature Comparison
Fuel & Hydraulic Fluid Exposure
Since these CIs are applied in areas routinely exposed to caustic fluids, namely hydraulic and fuel fluids, it is important to know how each performs under specific climatic or operating conditions.
Application Efficiency
We have talked about this a little bit already, but the application does matter. Non-curing pastes are best for areas with gaps that tend to flex and move. That sort of flexion will break a hard-cured sealant and render it useless, so non-curing CIs are used in those places.
Large areas with odd geometry and difficult accessibility are also often the most rigid parts of the aircraft, so a cured sealant is best used there. For example, it is commonly used in the wing box area, cargo bays, and landing gear wheel wells, all of which require absolute rigidity.
When Do You Use Sprayable Sealants?
Alright, when are sprayable sealants best deployed?
Large-Surface Corrosion Programs
Wing boxes, fuselage interiors, cargo floors, and structural bays are large, rigid areas that require a lot of sealant, and also are only stripped down during depot-level maintenance. This is the ideal time to recoat them, so the sealant or CI needs to last throughout the depot maintenance cycle until the next appointment, which is usually several years.
Consistent Film Thickness Requirements
PR-1436-GPT reliably produces a 5–8 mil dry film across large surfaces. It is very difficult to achieve uniform thickness across a large area using a brush or spatula; those products are meant for precision applications and, again, have a different consistency than sprayable CIs.
High-Fuel-Exposure Zones
PR-1436-GPT excels in tank cavities, fuel bays, splash zones, and Type III fuel environments where a rigid, cured sealant is the order of the day.
How Greenwood Aerospace Supports Federal Corrosion-Prevention Programs
Our goal when we set out to get on the GSA Schedule was to simplify the federal procurement process as easily as possible through our catalog of consumable products on GSA Advantage. All eligible federal and military procurement officers with a government purchase card can follow the link in this article and purchase the PPG CI sealants they need.
If you need bulk supplies, need to check on the status of an order, or have general inquiries, you can contact our dedicated GSA teams at: gsasales@greenwood.aero | 580-865-6000 | 833-GSA-EBUY.
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