Monday, February 11, 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 voil√†! - 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.



Anonymous said...

This product is such a contaminant the Boeing has special procedures for is use or should I say warnings. Even tools used durring application must be segregated from other tools. As for removal well lets just say never and I mean never use it.

Latitude 43 said...

The Jack Wagon that owned our boat previous, used it to seal the ports. I refuse to describe the agony of resealing so that I may sleep tonight.

Steve Hulsizer said...

I use a product called Autotech available from Prism Graphics. It is water soluble and works on silicone and most other sealants. It takes while, but leaves a clean surface. It was designed to clean vinyl graphics off of trucks and the like.

Unknown said...

I absolutely agree! I have a wood mast and the previous owner had used silicone to "seal" around the VHF antenna cable where it enters the cap at the top of the mast. The silicone just channeled the water into the mast and rotted the top few inches. I hate the stuff for all the reasons you listed, and it's hell to get rid of because you can't always see it until you try to paint or varnish. NO silicone on my wood boat and NO duct tape either except buried away in a locker for dire emergencies.

Drew Frye said...

I'm sorry, but you touched on my pet peeve; folks that use silicone during hose installation! It reduces the friction between the hose and the barb, is annoying to remove during maintenance, does not improve the seal in any permanent way, and will destroy the seal if the hose is shifted for any reason. Better, get a clean barb and use either K-Y or glycerine for hose lube. The propylene glycol or glycerine, respectively, evaporate in time leaving a tight residue-free seal. Some recommend grease, but most sanitation hoses are eventually degraded by grease. As for white sanitation hose, after testing and use, I have no use for it. There are now better rubber products.

There is one other proper use for silicone: on something unimportant where the PO used silicone. If you can't beat em'....

Certain port glazings; that is all for me.

Robert Salnick said...

Well Drew, I guess we'll have to disagree on this one. When I redid all the head plumbing on Eolian, I used silicone to ease assembly and seal the hose joints - a total of 30 of them. None have leaked in the last 7 years. Some of the short hose sections have been replaced in the intervening years - it was no big thing to rub the silicone off of the hose barbs, after cutting off the hose.


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