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FYI - Pro Seal As An Adhesive

HFS

Well Known Member
PPG Aerospace (maker of "Pro Seal") doesn't even list shear strength in their TDS (Technical Data Sheet) - only tensile strength, 370 psi - not very much when compared to the shear strength of 3M's Scotch Weld 2216 epoxy adhesive - 3200 psi. Almost 10x greater than Pro Seal!

I get that shear & tension strengths are not the same, but the fact that PPG doesn't even list shear strength as a product specification, makes me think they don't recommend using it as an "adhesive".

If you are looking for a suitable adhesive for strength enhancement - I would not suggest Pro Seal - it shears at such low loading conditions, that it actually acts as a lubricant.

I tested several Pro Seal coupons years ago (overlapped shear), and found micro movement across the face of the joint prior to failure. The Scotch Weld coupons tested resisted any movement (or at least discernible) until the moment of catastrophic failure, well above the loading for rivets only.

YMMV - But I bet not by much.

HFS
 
It's all about intended application.

Why would a company list a shear value for an elastomer not intended to be used as an adhesive?

Why would you not expect "micro movement" from a sealant that has to remain pliable for application on non-rigid surfaces?

Polysulfides are amazing elastomers with great chemical resistance; hence, their application to seal non-rigid fuel tanks and aircraft structures. Some original applications are still doing their job in B52s 60-70 years later per the Desoto engineers. My Mooney tanks had original sealant from 1969 (sold in 2019), though it helped that the fuel tanks were kept full for the last ~ 30 years of its life.

Obviously, products intended to be adhesives will should be better at that application. On the other hand if these polysulfides weren't such a great product, people would stop finding so many uses for them; intended application or not.
 
2 different animals..

I have used both extensively in heavy jet industry for over 40 years. The 2216 is just what it is..EPOXY, and its got fantastic ability to flex just enough to be the go to adhesive for bonding plastic stuff to metal stuff. I have glued fiberglass fender flares to race cars that bent metal before the glue fails. Proseal and other sealant like it also have specific bond/adhesive characteristics, and way more flexibility, but not for the same kind of application. It is specified for both sealant and adhesives in various maintenance manuals. Its fantastic for stuff that's not under heavy load and is subjected to vibration, ect., and its very paintable. ..but the two products mentioned have no common uses in my experience and opinion, except maybe wire run zip tie stand offs.
 
Sikaflex 227

Vans specify to use Proseal or RTV to attach the NACA air vents to the airframe skin. I'm trying out Sikaflex 227, an automotive body sealant, for this purpose. Proseal is not readily and reasonably available where I live, whereas Sika products are. The Sikaflex 227 tensile strength is 1.7 Mpa, so it would take a force greater than 1000 lbs to tear off the vent. The sealant can be painted over, which is an advantage versus RTV.
 
Vans specify to use Proseal --- snip --- to attach the NACA air vents to the airframe skin.
--- snip ---

The NACA vents on my RV-6 have been held in place with ProSeal ONLY for over 25-years and show no sign of wear or separation. Over 3,500-hours of flight time.

One MUST scuff the surface before applying ProSeal else the bond may or may not be secure.
 
Proseal as a sealant is very good in a wide range of applications (gas tanks, etc). It is also OK as an adhesive in a low shear load application, like a NACA vent. It might not be a good selection as an adhesive in a place requiring a moderate or greater shear load requirement. For an adhesive, maybe consider Scotchweld 2216 as previously mentioned, or G-Flex, or some other structural adhesive.
 
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