Silicone

[Dale Tanski]

I run into a lot of harsh opinions, misinformation and just plain wrong information and opinions regarding silicone on boats.  Many people will even say there is no place on a boat for silicone period.  I say... not so fast.

You will find silicone everywhere on our P365's.  In most cases, if you are trying to remove something, you will find that even after 40 years that silicone if properly applied is still pliable, flexible and holding strong.  For the most part I would regard silicone as much of an adhesive as a sealant.  Isn't that what we are typically looking for? Something that will keep moisture out and hold fast.  Almost every aquarium in the past 30 years is still holding water (as long as the glass is in tact) with simple silicone glass to glass joints.

The keys to proper application is a clean dry surface.  Typically the smoother the surface the better the bond.  The surface must be clean and free of foreign substances including dust.  Any moisture during application will greatly effect the materials cured effectiveness. If the surface is wet it will not stick. A wetted finger however is a wonderful thing to tool the surface and will not negatively effect the final product.  I have seen silicone applied in ultra low humidity conditions and it would not cure at all.  There are special blends of silicone that will withstand temperatures as high as 450 degrees F and are used for gaskets on internal combustion engines daily.

There is silicone and there is marine grade silicone.  This is probably where silicone gets its bad rap.  Big box store silicone for the most part is not suitable for UV exposure.  Exposed to sunlight it will turn orange and become brittle in less than a year.  Marine grade silicone (the expensive stuff) has UV inhibitors in it.  A good grade of Marine silicone will last for decades. 

Like everything else, silicone has its purpose. For the most part it is removable, remains flexible and long lasting.  I wouldn't use it for hull to deck joints but I could think and have seen worse products applied on big name boats.   

Just a few thoughts...

Dale
Obersheimer Sailor Supply
Frigid Buffalo NY

[S/V AMITY]

   Major problem I've found using marine silicone for bedding is if I need to apply a finish around the bedded area since even a trace film of silicone will reject paint & varnish. One silicone product I've used which is paintable and has excellent adhesion over a thoroughly cleaned surface is this:  https://www.homedepot.com/p/GE-Supreme-Paintable-Silicone-10-1-oz-White-Window-and-Door-Caulk-M90026-30/203370482 .  Uncured material cleans up with isopropanol.