Mfgr Says Use Only Silicone! WTH...Everyone Here Says Don't Use Silicone.

[SailFastTri]

I'd go with butyl -- either tape or caulk. It stays tacky and fills gaps, even when the materials move from expansion/contraction. If you ever need to repair or replace, it will let go without destroying the frame or surrounding surface.

[capngeo]

My understanding is that the silicone is spec'd for certain plastics because it is incompatible with typical marine caulking such as 5200

[roverhi]

Beckson uses a plastic that is not compatible with polysulfide and polyurethane sealants. Assume butyl is a problem as well or they would mention that as an acceptable sealant. The above sealants degrade the plastic causing cracks. An easy choice for me not to use Beckson Ports especially since they usually look like crap a few years down the line as the plastic degrades from UV. Don't know if other plastic port manufacturers use a different kind of plastic that works with the above sealants. I'd certainly make an effort to find a substitute that is.

Sillycone belongs in boobs not boats.

[chala]

When using silicone I prefer the neutral cure one, the acidic cure one do damage thermoplastic, make the plastic to swell.

[J_m]

When I spoke with Beckson on this subject, they actually recommend a specific silicon - DOW Corning 795. Not easy to find, As others previously stated, most marine sealants will degrade the plastic over time.

[Lake-Effect]

If Beckson is specifying silicone, I agree with the consensus that other sealants are likely incompatible with their plastic.

Our boat's side lights (windows) are simply acrylic panels screwed to the side. We removed them, cleaned the joint area, and remounted them using clear silicone in the "gasket" manner *... and this has worked very well. This is about the only place I'd use silicone on a boat.


* Silicone gasket: apply silicone, mount window with toothpick tips stuck between window and cabin to create space, snug up screws, when silicone has cured, remove toothpicks and tighten all screws just a little to compress silicone.

[Blue Stocking]

795 is available from any commercial glass shop. When it squeezes out around the edges, wipe it with an ice cube. Sets the surface quickly, and allow trimming with a knife.

[boatsail]

Just got off of the phone with Mark from Mark Plastics. He said that 795 is the way to go for windows. He is going my fixed ports. Very knowledgeable and answered all my questions and more. I'm going to be sending him a template of the windows this week for him to match up just to be safe.

[Cheechako]

Silicone has a bad rap with boaters for sure, it is very hard to get off down to a fresh surface. It works surprisingly well though. A fillet of silicone will come loose though... kind of a conundrum. If I were you , I might try using one of the commercial type silicone/poly blended sealants used for windows etc. Nicer stuff than regular old silicone. I had Becksons in my Rawson 30 thirty years ago, I 5200'd them in! No problem. That was probably one of my few 5200 mistakes though, thinking back, the Beckson's tend to break eventually, and getting one out must have been a "one piece at a time" affair for a subsequent owner.

[sailorchic34]

I should note that I use silicone sealant on my boat for bedding and sealing. I found it superior to lifecaulk and easier to use then 4200/5200. Plus its cheap and I am all about cheap . But I'm blonde and female and use other things on board the the typical CF sailor would not. But I'm not typical either.

[sailvayu]

The reason Beckson recommends silicone is because most plastics will leach oils (it is a oil based product after all.) Most sealants will not adhere well to plastics in general because of this. Silicone has a bad rep because so many boaters use the wrong stuff. Silicones are not all the same and the curing agents are different. If it smells like vinegar do not use it as this is the wrong type. I even found silicone sold under the west marine brand name is the cheap stuff and no better than what you get from the home improvement store for a fraction of what West charges.
So yse the Dow 795 is the good stuff, boatlife sells a good quality silicone and you can also use a hybrid like 4000 UV or lifeseal.
And it is a myth nothing will stick after you use silicone it just takes a bit more care in cleanup. What most do not understand with the other sealants is they leave a film too but because it acts like it sticks they think it is ok, truth is they are still just bonding to an old film and not a clean surface. At least with silicone you are forced to get to a clean surface.
Sailorchic if you are using the cheap stuff you might want to rethink what you use. Open the tube if it has that vinegar odor get something else. Saving a few bucks on sealant is a false economy as you are going to end up using it more often and doing the job twice. Buy the good stuff and you will not end up being one of those that hate silicone in the end.
For more info read my article on sealants Project Boat Zen - Boat and Yacht Repair and Restoration

[CarinaPDX]

Another good reason for not keeping the cheap vinegar-smelling silicone on board: if used to seal electrical parts it will encourage corrosion. The curing process gives off acetic acid (vinegar), and as an acid it is corrosive.

I suspect that the reason that Beckson calls for silicone is that it has since the days when BoatLife was the most commonly used sealant; that version of BoatLife was a polysulphide and would attack the plastic. The problem with polyurethane is not so much chemical incompatibility as thermal expansion; acrylic (Plexiglas) has a high TCE (temperature coefficient of expansion) and swells/shrinks a lot with temperature changes while the polyurethane adhesive-sealants (e.g. 5200) are usually too rigid.

Greg

[sailorchic34]

Oh agree the cheap silicone is nasty. I use 3m I think, generally black and natural curing. Black for bedding as its easy to see to clean up.

[Azul]

I remember Compass Marine saying port lights was one exception to the rule against using silicone. Silicone penetrates gel coat and must be ground off to remove residual before painting etc.

[FSMike]

When I redid the aft cabin about 1&1/2 years ago I put in two Beckson opening ports and used silicone per their recommendations. So far so good.
A year and a half is too long for my feeble mind to remember what brand of silicone it was.