Tuesday, February 19, 2013

Silicone rubber: Just say NO!

I despise this stuff.

No, that's not a strong enough word - I HATE silicone* rubber.  There, now I feel better.

It's a weak adhesive.

It cannot be sanded.  Or painted.

Nothing sticks to it - not even silicone rubber.  Except dirt.

If you have ever used it on a surface, that surface is almost irretrievably contaminated.  The only certain way to decontaminate a silicone fouled surface is to remove that surface, by sanding, sand blasting, etc.

Eolian's previous owner loved the stuff. 

I can think of only three places on a boat where silicone rubber is called for:
  • There are some plastics that cannot tolerate contact with polysulphide, polyether or polyurethane adhesives or sealants.  Where the manufacturer (notably Beckson, for their ports) requires it, you should use silicone rubber.
  • Lubricating/sealing head hose during assembly.  Apply a coating to the inside of the hose end, carefully heat it with your heat gun until both the main body of the hose and also the stiffening spiral have become soft, and assemble.  Get the hose clamp on while the hose is still soft if you can.
  • Making non-skid rings on the bottom of dishes, serving bowls, etc.  Put down a piece of wax paper, run a bead around the bottom of the dish or bowl and set it on the wax paper.  When the silicone is cured, peel off the wax paper and voilà! - a nonskid dish.
Anywhere else on the boat that you think you might use silicone rubber, polysulphide is probably the correct choice.  You might possibly know polysulphide by its other name: BoatLife Life Calk (yeah, that's how they spell it).  Another choice could be a toned down polyurethane, like 3M-4200  (but stay away from the full-blown stuff - 3M-5200, unless you intend for the installation to be permanent).

Now put down that caulking gun and step away from the boat!

* A little definition is in order.  Silicon (note the absence of the trailing 'e') is a silvery metallic substance - here's a picture of a piece I have on my desk right now:

I should know - I used to work in a manufacturing facility that made the stuff, starting with quartz.  Silicon is the basis for most semiconductors made today, albeit in a more purified form than that chunk on my desk.  It is also dissolved in copper along with other stuff to make silicon bronze.

Silicone is a term that is used to refer to a whole series of compounds based on silicon, in much the same way as the term carbohydrate or hydrocarbon are used to refer to a whole series of compounds based on carbon.  Silicone rubber, silicone grease, silicone oil (in silicone breast implants - not silicon, Heaven forbid!) are silicon compounds.

Sadly, the press seems to use the terms more or less interchangeably, indicating that they have no idea what they are talking about.  But then I repeat myself.

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