Side Window Installation Sealant

[Rob58]

No doubt there are dozens of sealant/adhesives out there, but some must be better than others. I want to install some side windows. Looking for a material that will handle the bonding task but will also allow me to form a nice tapered border to smooth out the step between the aircraft skin and the acrylic window. Finding something that can be troweled to look clean seems to be a bit elusive. Anyone have a recommendation that has worked out well? TIA

 

[Stewartb]

Dow 732 silicone. Clear. If you trowel an edge it’ll attract dirt and discolor. Minimize it.

 

[MooneyDriver78]

I think they use the same stuff they use to seal fuel tank inspection panels (PRC), it’s black and very robust. There’s different grades, the grade for inspection plates is less adhesive.

 

[Bell206]

Anyone have a recommendation that has worked out well?

I always recommend one should follow the OEM process when it comes to window installs to include the sealants. In some cases the window may need the ability to "move" once mounted so using a different method or material may inhibit that movement. And in the case of sealants not all have the same qualities or benefits. For example, some sealants have very high bonding properties and may lead to damages during the next window replacement cycle. Or may have adverse chemical properties as with acid cure silicones which can attack the aluminum and lead to corrosion issues.

As to the "trowel" effect there are several install methods available to accomplish that, if appropriate to the installation process.

Do you have particular aircraft in mind?

 

[Walboy]

Based on a recommendation from an A&P/IA friend, I used 3M Strip Caulk Window Sealant I purchased from Spruce. It works ok, but continues to ooze out two and a half years after installation. This was on a Piper. Maybe I used too much, I dunno. I used enough so that it would "squish" out to ensure there was a good seal and then cleaned off the excess. I think if I were doing it again, I'd try to find the OEM material as @Bell206 recommends. The 3M material definitely allows for the movement of the window.

I will also say that I used silicone on a window, not knowing any better. I'm happier with that seal on than the window sealant but it does not allow for window movement.

 

[robin ardoin]

3M Strip Caulk is a butyl rubber compound. Excellent sealing properties for harsh environments such as marine and aviation. However, there are nuances that must be considered when using butyl rubbers. The material never gets hard. It is thixotropic, that is, it remains flowable under pressure. In marine use you have to tighten the window or hatch frame incrementally over about a month. This will allow excess material to flow out that can be trimmed with a plastic 'razor' if need be. I tighten the frame 3 times in a month...first when installed, then a little more snug on the fasteners a week later, then final desired torque at about 1 month post install. It is a very durable and reliable sealant in the marine environment.

 

[Stewartb]

Tighten the frame? You haven’t installed airplane windows, right?

 

[robin ardoin]

Tighten the frame? You haven’t installed airplane windows, right?

No, I haven't. Just explaining the 'squish' associated with butyl rubber compounds. I've used the same material in other applications. Now, go get your shine box!

 

[Stewartb]

Aircraft window frames are riveted with driven rivets. No adjustments. Silicone is a great sealant and easy to amend after completion.

 

[Walboy]

Aircraft window frames are riveted with driven rivets. No adjustments. Silicone is a great sealant and easy to amend after completion.

The brackets that hold the plexiglas in place in a Piper are not driven with rivets. They are held in place with screws. However, the arrangement is such that one cannot periodically tighten them to get a better seal if that makes sense.

 

[murphey]

Aircraft window frames are riveted with driven rivets. No adjustments. Silicone is a great sealant and easy to amend after completion.

My windshield is riveted. The side windows are held in place by the two frames (inside & outside) that are screwed to the fuselage on the Pipers. I used the 3M also, did an ok job, the shop still teases me about it. But it's been flown thru rain without any leaks. Could have been neater but I didn't feel like paying $125/hr for them to do it.

 

[Rob58]

I think they use the same stuff they use to seal fuel tank inspection panels (PRC), it’s black and very robust. There’s different grades, the grade for inspection plates is less adhesive.

This picture you posted illustrates the transition that I want to accomplish installing the side windows - a narrow border of sealant between the edge of the window frame tapering out by .25" - looks good and should create a great seal. I am putting the sides windows (with frameless vent window) in my AC-500 - same windows from Great Lakes Aero Products that you have shown in this picture. Thanks for the image and the reference to the PRC material.