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post #17 of Old 05-30-2013
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Re: LifeCaulk vs. 3M 4200

Originally Posted by gedaggett View Post
Dow Corning 795 is a great product. I have used it on everything from retrofit polycarbonate windows on Catalina 30 (no fasteners just the adhesive) to sealing the mast, chainplate, deck cleats. It is very versatile and unlike the 3M products doesn't require etching or scuffing on polycarbonate or acrylic materials. Great product. (disclaimer: I have no vested interest in Dow Corning)
I'm curious what other people say but I think the issue with Dow 795 is that it's silicon based and therefore has the contamination and other issues associated with that. This is what sailingdog said in his well known sealant post:

Originally Posted by sailingdog View Post
Silicone-based sealants aren’t really sealants IMHO. They’re really gasket materials, and need to have a minimum thickness and be kept under compression to work properly. Silicone-based sealants should only be used in above-the-waterline applications.

The only structural silicone sealant that I generally recommend is Dow 795. This is a structural adhesive which is generally recommended for bedding ports. It is not your common silicone caulk. However, beyond the very specific use of bedding acrylic* ports, it should not be used on boats.

Aside from bedding acrylic and polycarbonate ports, and certain plastic parts, like Beckson ports, and covering the exposed ends of cotter pins—it really has no place on a boat—primarily due to the residual silicone contaminants silicone can leave behind. These contaminants are almost impossible to remove thoroughly, and will prevent other sealants and paints from adhering to the surface properly. Even strong adhesives, like epoxies, have trouble bonding if the surface has silicone contaminants on it.

One other use of silicone is for sealing potable water tanks. However, I highly recommend that you use only NSF approved silicone sealants for potable water tanks and systems. These will not have any toxic components, unlike some of the other marine-grade sealants which may contain isocyanates.

Some silicone sealants are acid-curing and should never be used on metal. These are generally easily detectable by the strong vinegar smell caused by the acetic acid that is contained in them.
Marine Sealants in a Nutshell

That said, if Dow 795 is as strong as described, I'm not sure why exactly it's not suited for other tasks, assuming you don't care about the contamination issue. And I'm not sure why you would if you planned to use Dow 795 or other silicon going forward.

Last edited by asdf38; 05-30-2013 at 01:20 PM.
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