[TowerTalk] silicon sealant

K8RI on TowerTalk K8RI-on-TowerTalk at tm.net
Sun Oct 22 21:11:01 EDT 2006

----- Original Message ----- 
From: "Jim Lux" <jimlux at earthlink.net>
To: <K7LXC at aol.com>; <towertalk at contesting.com>; <k2mme at juno.com>
Sent: Sunday, October 22, 2006 12:57 PM
Subject: Re: [TowerTalk] silicon sealant

> At 07:55 AM 10/22/2006, K7LXC at aol.com wrote:
>>In a message dated 10/21/2006 4:32:53 A.M. Pacific Daylight Time,
>>towertalk-request at contesting.com writes:
>> >  I have used various forms of silicon sealants for years and  it seems
>>they all have the same problem.  They seem to be made for  single uses.
>>By that I mean they harden in the tube. I'm sure the  manufactures love

The main problem with these is once opened the caps don't really seal the 
tubes well. On top of that most of the RTV family of products reguardless of 
who makes them has a shelf life of about two years even when not opened.

>>this.  I'm not talking  about cartridges but  tubes for small uses. Is
>>there a specific product that I can use , recap  and use again and again
>>in small amounts?

After use, squeeze out a bit of excess, then tighten the cap down on that. 
Yes, it'smessy but that cap has to be sealed tight. If there is a void at 
the top when the cap is put in place even that moisture is enough to cause 
quite a bit of curing.  I don't expect a tube that has been opened to last 
more than a couple of months. Anything more than that I consider a bonus. 
I've had tubes of the building calk turn into one chunk of Silicone rubber 
without ever having been opened.  Keeping them at near 40 degrees *might* 
help prolong their shelf life.

>>I'll assume you're using silicon sealants for  antenna and feedline
>>connections. RTV (room temperature vulcanizing)  materials are
>>mostly the wrong things
>>to use. The problem is that they outgas  acetic acid while they cure.
> Not all RTV outgasses acetic acid.  Depends on which kind and what
> chemistry is being used for the cure process.

Even then when used outdoors or in unconfined spaces they usually aren't a 
problem. I've used them for years at antenna connections. OTOH I'd not use 
those particular mixes for circuit boards <:-))

> The acetoxy chemistries outgass the acetic acid.  I believe the
> methoxy chemistries are non-corrosive.
> RTV as a product name is trademarked. Other companies make the same

Actually it's "Silastic RTV" that is trademarked.  The RTV part has bretty 
much, like "Deep Freeze",  become generic. There are now companies selling 
RTV, RTVs and various forms of the name using RTV.  It's like fighting 
people calling the white foam cups, Styrofoam cups as they are not. 
Styrofoam (TM) is a blue building material.  The company (Dow Corning) used 
to get pretty specific in having us use the words "Silastic RTV" when 
describing or talking about the DC products. The company across the road 
(Dow) would get down right excited when they heard those foam cups referred 
to as Styrofoam cups<:-))

> kind of products and they're not called RTV, so sometimes searching
> on more generic terms is useful: Silicone potting compound or

On RTV I received over 36 million 400 thousand results.

> silicone sealant.  You'll also see RTV used as a descriptive term.
> Most of the "good" electrical potting silicones are a two part, with
> very long shelf life for the two parts.  They use a different variety

I even had some heat sink compound like that.
It sure was messy, but once cured you sure didn't have to worry about the 
heat sink coming loose.

> of curing methods. Some are sold in those nifty dual syringes like
> they use for epoxy adhesives, but I don't have my catalog handy to
> look them up.
> There's also Urethane potting compounds, as well as Silicone.

I use Vinyl Ester resin as I have a lot of it around.  I think I have about 
3 gallons right now. One gallon is promoted while the other two have not 
been unsealed. Unfortunately it has a relaively short shelf life and even 
shorter once promoted.

Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com (Use return address from home page)
> I used to buy stuff from Silpak (http://www.silpak.com/) they have a
> wide variety of stuff that they sell in various quantities and
> dispensing methods.  They could probably tell you what's practical
> and what's not.
> I'd check DigiKey or Mouser catalogs as a start.  Or go to the GE website
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