Sillycone is the spawn of the devil. My first boat came from the factory with everything bedded in the sh*t. Spent my first year of ownership
R&R'ing every fitting on the boat because of the leaks
. Sillycone will bond to some materials, especially porous materials, but it doesn't bond for beans to FRP gel coat and metal fittings. When they are subject to stress, the seal goes away and leaks
become a water
fall. What was the most frustrating part of it was the stuff leaked like a sieve but was damned hard to remove so I could rebed with Life Caulk.
What really makes Sillycone bad is it is a bear to work with. Hard to clean up and even a slight film of missed residue will collect dirt and look terrible. Trying to clean up any missed areas is one of the most frustrating parts
of sillycone. Haven't found anything that will cut the cured stuff. If any one knows of a chemical that will do the job, let me know. Sillycone also shrinks when it cures. This can leave voids or holidays if you cinch up the part tight from the beginning.
One of the PO's on my current
boat was a compleat idiot. They used sillycone on everything they put down which is only a small part of their stupidity. So I'm once again tearing off every one of those fittings to rebed with LifeCaulk as there are numerous leaks where the sillycone was used.
I really like LifeCaulk. I've had a 35 year history
with the stuff and it's still going strong on my old boats. It remains pliable and holds a bond even with repeated torquing of the fitting. The fittings can be removed with a little effort if need be. You can clean it up with Acetone after it's cured and with paint
thinner before it cures. It's relatively easy to work with, at least compared to Sillycone and 4200. It's less viscous than 4200 so easier to spread around and seems a bit more sticky in clinging to parts
I haven't used 5200. The main reason is its reputation as a permanent adhesive. Hear it's near impossible to get fittings up that have been bedded in it. So far haven't bedded anything down that I thought would be down permanently. When I redo the chainplates, will probably use 5200 cause I don't want them to leak and hopefully will never have to take them up again.
Both 5200, 4200 and LifeCaulk will cure in the presence of water, in fact require moisture in the air to cure. For fittings that are going right back in or already in the water, they are ideal.
One word of caution that has already been mention in other posts, some plastics don't get along with 5200/4200/LifeCaulk. Check with the manufacturer of any plastic fittings to see what bedding compound works for them. Personally, it a part doesn't work with LifeCaulk, I wouldn't consider using it.
Not sure when 5200 came into wide use. In the '70s, a white sticky bedding compound was probably LifeCaulk or 3M 101 sealant
. Both are Polysulfides. IIRC, 5200 was not around then or hadn't gained widespread acceptance.