stan wrote:
"George" wrote in message
. ..
stan wrote:
I've got sort of a specail project going where I put the caulk on
something about the size of a half-dollar coin.

Imagine putting a small bead on the coin's face, then spreading it around
with your finger. What happens of course is the caulk fills in and
covers the small depressions while the higher area's (like the
president's face) you can see still see because your finger sort of
"squegees" it off.

Now if I let the caulk cure on the coin for 24hrs what should I find on
the president's face? I would think nothing but there is actually a
greasy residue which I did not expect.

This is 100% silicone:
http://www.caulkyourhome.com/sil2_kitchen_bath.html

I rub a blue colored old T-shirt on the raised area's of the coin and it
comes away darker like it was wet or greasy (even after 24hr cure). If I
put a small bead of caulk on a piece of paper (without smearing it) and
let it cure, it looks and feels rubbery like normal caulk with no greasy
residue, even if I pull it away from the paper.

Any thoughts on how this is occuring?
Likely the acetic acid that was liberated during the curing process
attacked the metal. There are other formulations that are not peroxide
cure that will prevent that.


Ok thank you for educating me. The label for for GE silicone II caulk says
the curing process releases Methanol and Ammonia but I think that's not any
better. To add some more detail, this is actually an electronics
application but I just used the coin as an example of the surface. The
caulk/sealant will touch solder and a silver based paint (85% silver) which
need to remain un-corroded and electrically conductive.

I may need some type of electronics grade sealant but it has to have a
service temp of -40C to 110C when fully cured. Here are some things on my
short list:

star brite liquid electrical tape:

http://www.starbrite.com/sproductdetail.cfm?ID=1076


dow corning 744

http://www.dowcorning.com/applicatio...7EN&DCCSF=21EN


dow corning 3140

http://www.dowcorning.com/applicatio...7EN&DCCSF=21EN



You are looking at the right stuff. Those Dow RTV products are
specifically designed corrosion sensitive applications. I think the 744
is likely the most appropriate one for the use you described.