Re: [IRCA] moisture proofing boxes

[Rick Kunath <k9ao@xxxxxxxxxxx>]

Craig Healy wrote:
> Automotive silicone seal is more fluid than the hardware store
> kind, and will fill the corners better.

That's likely RTV #736. (Room Temperature Vulcanizing) This is the 
flowable RTV. #732 is the stiffer stuff that is sold as caulking and as 
GE silicone sealant. #736 is often sold as windshield sealant because it 
flows into the cracks in the rubber gasketing. Both formulas of RTV 
silicone release acetic acid while curing, so you'll want to be sure 
that the innards of the box can handle this before filling up the box 
with the stuff.

Epoxy might be another choice for potting. A Google on "potting 
compound" will return some info on stuff made for electronics. These are 
generally a two-part formula and are mixed just before use. Some are 
made to transfer heat well, others don't. But I doubt heat issues would 
matter in this application.

< If I can fill the box above all the
> parts, then put the cover on, it will prevent any water from getting to the
> components.  Won't work with a potentiometer inside, however.

Yes, that you'd still have to mount outside the epoxy, but you could 
cover the pot housing with varnish to waterproof/fungus proof it. We 
used to do that with milspec modules a lot. Some of the Bourns pots are 
sealed pretty well, especially the multi-turn ones.

> Normally potting compound is a type of epoxy.  No clue where to get that in
> the quantity needed to fill a box.  Maybe a boat supply house?

Generally the electronics stuff is specially formulated to not shrink 
during curing and to radiate heat while retaining insulating qualities.

Rick Kunath
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