From: dingbat@codesmiths.com (Andy Dingley)
Newsgroups: rec.autos.tech
Subject: Re: Can I use Silicone caulk?
Date: Mon, 17 Jun 1996 13:22:23 GMT

The moving finger of Cliff_Lum@mindlink.bc.ca (Cliff Lum) having
written:

> Well I guess your mechanic made some money off you. Right off a GE
>Advance Technolgy Silcone II Caulking gun container. 

It depends what you mean by "silicone". Most silicone sealers (oh sod
it, damn near _all_ of them around here) will release acetic acid on
curing. It's not a big deal for steel, but it's a bad idea on
non-ferrous metals (copper, brass, aluminium) and it's a death
sentence for electrical parts. You can buy electronics grade silicone
sealers which cost more, work no better, but don't produce the acid.
If you're trying to waterproof car electricals, make sure you get the
right one, or you'll cause more trouble than you solve.

NB - This is for one-part self-curing silicone compounds. Silicone
grease or silicone oil are safe on both electronics and rubber
components.

Silicone isn't the right stuff for panel sealing. The viscosity is all
wrong and it's not adhesive enough. Go to a commercial bodyshop
supplier or motor factor and buy a paint tin of "brushable joint
sealer". It's much easier to apply this stuff by brush than by nozzle.

For small repairs, I don't bother anyway. If you're painting by brush,
not spray, it's no big deal to work paint into the seam with a brush
and squirt Waxoyl into the back of the seam later.


BTW - Old silicone brake fluid is perfect for putting a shine on
rubber clothing     8-)

From: dingbat@codesmiths.com (Andy Dingley)
Newsgroups: rec.autos.tech
Subject: Re: Can I use Silicone Caulk?
Date: Tue, 18 Jun 1996 23:06:11 GMT

The moving finger of Cliff_Lum@mindlink.bc.ca (Cliff Lum) having
written:

>>  Silicone isn't the right stuff for panel sealing. The viscosity is all
>> wrong and it's not adhesive enough. Go to a commercial bodyshop
>> supplier or motor factor and buy a paint tin of "brushable joint
>> sealer". It's much easier to apply this stuff by brush than by nozzle.
>>
> It sure seems viscous enough to me. 

That's what I meant. Silicone is _too_ viscous. A "caulk" is usually
intended for building up an external fillet, like around a bathtub.
What we want here is a mastic, for sealing between two panels. Caulks
need to build up the raised fillet, so they're viscous and
quick-skinning, neither of which are useful properties here.

>It seems to have superior adhesion which it says right
>on the container. 

Maybe you have a high grade of silicone which is stickier than usual.
It's still not 

I drive a Range Rover, made of bolted aluminium panels stuck together
with a polyurethane mastic. Many servicing operations require the
removal of these body panels, and their subsequent resticking. I
always buy the right grade, even though it costs me three times as
much as silicone and the tube goes rock-solid a few weeks after
opening. You can tell the ones which are held together with silicone
when you see them on the road, they're the ones with "strings" of
fallen-out sealer dangling from their panels.


>why go to all the trouble buying some commercial joint sealer and Waxoyl
>the back seam. 

Because you're trying to stop your door falling off next winter. If
all you want to do is slam it back together ASAP, then why seal it at
all ?

>The auto companies may use this method because its
>a faster method on the prodcution line. 

No they don't, they use it because they're going to spray paint the
panel afterwards. If you're brush painting, you don't need the sealer
at all.

> Are you sure were talking about the same stuff. 

No, because I don't see GE silicones for sale around here. Ours are
mainly Dow Corning, European or unmarked.