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Silicone versus RTV

Stockmanreef

Well Known Member
The RV-14 plans are great, but I this little thing always bothers me. At times it calls for an RTV and at times it calls for a silicone. Silicones caulks are all RTVs. Room temperature vulcanization--RTV. I can't say for sure that all RTVs are silicones, but I can think of an RTV off hand that is not a silicone--at least a commercial product.

I just find this weird. Maybe the plans should specific whether the silicone can withstand unusually high heat.
 
If it smells like vinegar, do not use it on any metal surface.

On the contrary, I was told by VANs that for stronger/better bond, Red RTV is preferred due to just that reason. Also, Red RTV is the choice of RTV for the FWF area which is used mostly in the metal part (baffles)
 
Which RTV

I've always used Permatex Sensor Safe High Temp RTV - it does not have the vinegar (acetic acid) smell. It comes in Black or Copper (not quite as Red as the smelly red RTV).

I've never had a problem with it not sticking - in fact the opposite. It's a bear to remove. I use the FWF and for general purpose use.
 
On the contrary, I was told by VANs that for stronger/better bond, Red RTV is preferred due to just that reason. Also, Red RTV is the choice of RTV for the FWF area which is used mostly in the metal part (baffles)

Acetoxy Cure and Neutral Cure Silicones

The most commonly used RTV silicones are acetoxy cure silicone and neutral cure (oxime) silicone. Acetoxy cure silicone has a relatively fast curing rate and a short tack-free time, providing a good, quality adhesion, although it is corrosive to metals. This type of RTV silicone releases acidic acid, producing a vinegar smell as a by-product. Oxime, or neutral cure silicone, on the other hand, is non-corrosive and has excellent oil and temperature resistant properties. This type of silicone produces a neutral/non-acidic byproduct that does take longer to cure and has a longer tack-free time. Let’s take a closer look at these two kinds of silicones.

https://www.gluegun.com/blogs/news/88695364-rtv-silicone-a-comprehensive-overview-and-product-guide
 
Acetoxy Cure and Neutral Cure Silicones

The most commonly used RTV silicones are acetoxy cure silicone and neutral cure (oxime) silicone. Acetoxy cure silicone has a relatively fast curing rate and a short tack-free time, providing a good, quality adhesion, although it is corrosive to metals. This type of RTV silicone releases acidic acid, producing a vinegar smell as a by-product. Oxime, or neutral cure silicone, on the other hand, is non-corrosive and has excellent oil and temperature resistant properties. This type of silicone produces a neutral/non-acidic byproduct that does take longer to cure and has a longer tack-free time. Let’s take a closer look at these two kinds of silicones.

https://www.gluegun.com/blogs/news/88695364-rtv-silicone-a-comprehensive-overview-and-product-guide
Looks like the information I had received from VANs tech support was not as good as it should have been.
 
One more data point, from the FAA:

AC 43-4B, 4.13.6.3.2

Silicone sealing compounds generally consist of one component which cures by reaction with moisture in the air. If silicones are applied too thickly or in such a way as to prevent moisture from entering the material, they may not cure at all. Many silicone sealing compounds also produce acetic acid, which has a vinegar smell, while curing, and can lead to severe corrosion problems. Limit silicone sealing compounds on aircraft to those noncorrosive products conforming to MIL-SPEC MIL-A-46146, Adhesives-Sealants, Silicone, RTV, Noncorrosive (For Use with Sensitive Metals and Equipment).
 
We used RTV for over 30 years in airliners, GA aircraft and helicopters, while it’s ingredients where known as a possible corrosion issue, that is only during its cure phase which is way to short to have any effects. Never in the thousands of aircraft I’ve worked on have I seen corrosion as a result of using the sealant.
 
Also keep in mind that silicone won't stick to aluminum oxide any better than paint will. If you are applying a bead externally (as opposed to between riveted skins) prepare the surfaces the same way you'd prep for paint: scuff immediately before application, or alodine ahead of time.

I'm partial to 3M FireBarrier 2000. A bit pricey but such a joy to work with. No acetic acid.
 
Would not use rtv between skins, filets only. Pro seal A is best for skins joints.


Also keep in mind that silicone won't stick to aluminum oxide any better than paint will. If you are applying a bead externally (as opposed to between riveted skins) prepare the surfaces the same way you'd prep for paint: scuff immediately before application, or alodine ahead of time.

I'm partial to 3M FireBarrier 2000. A bit pricey but such a joy to work with. No acetic acid.
 
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