.....it was my rant on
silicone on the other thread... I am teased about being a bit over expressive on the subject. It is the result of some personal suffering based on
silicone and DPO's...
Silicone is an inexpensive sealant that works well as a compression gasket (as has been mentioned in this thread already). I Like
silicone for mechanical gaskets, where metal on metal (or metal on plastic) sealing where slightly
(very slight) imperfections in surfaces may cause leaks. Something like waterpump (with care not to allow any globs to fall into the cooling stream for fear of causing clogs).
I am sure that the port mfg cited likes
silicone, as it does not harm the ports, and allows some flex between the metal port frame, and plastic (plexi) or glass ports.
Having said that, I believe that there ought to be a law banning
silicone on docks, in marina's or anywhere within 10 miles of any boat that is not designed to be scrapped before it is 10 years old....
.... Ok, maybe a LITTLE bit harsh... but just a little.
Why>?
Silicone oil (present in
silicone caulk) is made up of VERY small molecules. It bleeds from the caulk into any porous or semiprous medium. While the
silicone comes off easily, the oil remains.
Silicone is impervious to water, alcohol, acetone, or any petroleum-based solvent. There are some 'release agents' marketed for
silicone, they are expensive and only work to remove the
silicone caulk, not the oil. There are '
silicone solvents' marketed, they can wash
silicone off the surface but not out of the underlying material (in my experience).
They are also pricey, so you are not going to want to use any real quantity of them.
Surfaces that have had contact with
silicone not only will not hold paint, they do not prime well (primer does not bond) nor will epoxy bond to these surfaces.
Auto painters will tell you that
silicone wax makes their job difficult. The
silicone causes 'fish eye' which they can add an additive that increases the surface tension of the paint, but can promote chipping. THe problems with auto paint are not as serious since sanding can remove the paint which is where the
silicone is carried.
Fiberglass, and wood 'wick'
silicone oil deep below the surface. Sanding does not remove the oil, and can actually make the problem worse by spreading it around.
In my experience, I have painted, and had the paint lift. I then sanded and washed repeatedly with different products... to no avail.
I even went so far as to conduct 'pull tests' where I epoxied a block of scrap wood to the fiberglass I had tried to clean and prepare..... I was able to knock the block of wood off the epoxied (west, unthickened) surface with a tap from a screw driver handle.....
After several attempts to address these problems I took to using a sharp chisel to carve out the top 3/16 or so of the contaminated glass, and built up new glass to cover it...... much more work then it should have been. >
Admittedly I am a bit anal about some things, but watching paint chip off of a newly painted surface can really ruin your day.
Even taking such extreme steps, I found an area the other day where I did not get it all.. and there is a small crack in the paint where it failed to bond (like you get if you paint over the waxy blush west leaves.)
Everyone does what they think is best for their own boat. I won't even use
silicone on the window frames, as I might want to repaint the fiberglass that surrounds it. My hull was laid in 1964, and she is a 'good old boat', maybe that is why I think about the maintenance I do with a longer range view. I plan to keep her for some time, and want whatever I do to her to be good work, or at least something that leaves the boat better then I found it.
OBTW, I think it was last year Good Old Boat did an article on caulks and sealants and they only recommended
silicone for windows, and cautioned against getting it on fiberglass and wood…. so it is not just me.