Actually speaking of old timer your Butyl Rubber was invented in 1931 and it is cheap... I did't realize we were working on a house gutter system, flashing or sidewalk joint. This stuff never really cures.
I prefer a catalyst base compound- RTV silicone rubber
RTV Silicone Rubber will reproduce fine details and is suitable for a variety of industrial and art related applications including prototypes, furniture, sculpture and architectural elements. RTV Silicone Rubber can be used to cast materials including wax, gypsum, low melt alloys/metals and urethane, epoxy or polyester resins (without using a release agent).
RTV Silicones industrial applications include aviation, aerospace, consumer electronics and microelectronics. Some aviation and aerospace product applications are cockpit instruments, engine electronics potting, and engine gasketing. RTV silicones are used for their ability to withstand stress and temperature extremes.
Both make an excellent seal, it depends what you want old-skhool or
new-school...
It really isn't the difference between old school and new school it's a different application all together
RTV's make great molds they make great trinket pieces they make great silly little rubber bands that the kids all used to put on their wrists for some reason. and yep works pretty good when you have 2 pieces of metal or plastic's being bolted together or screwed to another solid piece to stop most movement. (notice I said bolted or held together another way) and they make super detailed casting molds but even you posted the main problem with using RTV rubbers. here's the problem in bold.
"RTV Silicone Rubber can be used to cast materials including wax, gypsum, low melt alloys/metals and urethane, epoxy or polyester resins
(without using a release agent).
they just don't usually stick to anything well. (except itself)
they DON'T make a good sealant between synthetic rubber compound seals and a painted or metal surface. there is just too much flex and expansion (or movement away from the petal or seal)for it to be effective allowing moisture to penetrate during the expansion and contraction process. Yes it takes a bit of time for it to happen but it does happen.
Go to an RV place (or better yet go to a Prevost motor coach place and tell them you put silicone RTV on the roof or windshield of your motorhome/motor coach to seal it from leaks . watch then tell you you have just voided ALL warranty's that you might have had(that is after they quit laughing tell you that you now have a 500,000.00+ dollar swimming pool) . Silicone rubber RTV doe not work well with a rubber seal (*or roof) and can cause corrosion and rust issues.
We did a lot of in-house repairs for the dodge and Chrysler dealerships if there was a constant "leaker" or a vendor defect.
If I saw that(silicone in the seal channel) when I was working at the Chrysler Glass plant I'd tell you that you really didn't want me to fix it did ya. If it had been siliconed we just shipped it back to the dealer and told them to tell the customer that they need to either buy a new seal and we would replace the windshield for free or the dealership could remove ALL the silicone and the seal (or remove silicone, butyl and windshield)then ship us the (Old)windshield(for shift/furnace/operator/packer check, someone was going to get some unpaid time off!) and car and we'd fix it if there was no trace of silicone.
now butyl is a different story. I love the 2 part butyl that you can now get over the counter. 10-15 years ago you couldn't find that stuff off the shelf, you had to be an installer or a repairman(I used it at work and got some repair tubes occasionally). It does NOT cause corrosion and does solidify to either a shore 50 or shore 80 hardness. (50 = uuumm about gas station squeeze blade material, 80 = a little bit more than sticky slick tire compound) AND it does a minimal movement due to thermal expansion. Sticks solid to anything pretty much(HDPE might be it's only problem that I have seen). but putting silicone RTV on even Butyl is still an issue due to the expansion problems(in RTV) that let water in since it doesn't stick completely to the surface and or moves during expansion contraction.
Catylist based RTV are a bit better but nowhere near as good as a 2 part Butyl for durability and pure stick to everything-ness. that's why you see 99% of the car makers use it, oh and it's more expensive than RTV so you think they'd use RTV instead of butyl wouldn't you.
if I run out of 2 part I use the single part and just wait for it to cure.
