Originally Posted by Ted S.
Why would I not use silicone? Just curious, silicone is commonly used for exterior aluminum fabrications, curious why it would not be used on an Airstream?
This is quite a controversial subject around here. Conventional wisdom says silicones and Airstreams do not mix. I suspect that has to do with 2 facts:
1) Most silicones the consumer has easy access to at home improvement stores releases acetic acid when curing and thus is corrosive. The irony is that the etching of aluminum due to the release of acetic acid actually increases the bond.
2) Nothing much sticks to cured silicone and removing all of the residue to re-caulk can be more difficult or time consuming than with some other sealant materials.
Based on my industrial experience with silicone RTV sealants however, I believe/know the following to be true:
1) There are RTV silicones that do not release acetic acid during curing, and thus are not corrosive.
2) Cured silicones can be wiped with solvents to soften the surface layer and additional silicone successfully applied, albeit with reduced bond strength.
3) Silicones are very resistant to temperature and UV. We used to use silicone to bond instrumentation to radomes to test them in a high temperature burner to simulate supersonic and re-entry conditions - the silicone was completely unfazed.
In my opinion (which will likely not be popular here), the primary (only) reason to possibly avoid silicones is the difficulty of repair/re-application. I suspect they actually hold up better than many of the beloved sealants historically used on Airstreams.
Note that the Adseal materials the factory is currently using on the roof and window "eyebrows" is
RTV silicone. And while some on here have taken Airstream to task for using it on recent trailers, I suspect the factory is using it due to better survivability in the field. The stuff is fairly pricey (and imported) so I'm pretty sure it isn't just a cost saving ploy.
As an anecdotal example, I had a range fan vent hood leak when I got my 2005 trailer. Being new to Airstreams but not new to aerospace manufacturing or construction techniques, I applied some clear silicone sealant around the periphery of the exterior hood and over the screw heads. Fast forward 11 years to when I sold it - the silicone still looked great (just not as clear), adhesion was good and there was absolutely no cracking/checking due to UV exposure. The polyurethane sealants used on the windows and roof from the factory did not fare as well. In fact, the roof had been resealed once at about 5 years and the material checking/cracking again. Time will tell, but I won't be surprised if the Adseal silicone on the new trailer holds up significantly better to the elements.