On Sun, 05 Oct 2003 11:19:40 +0100, Bob Minchin
wrote:



I expect the silicone is sticking to the rust and that the rust itself
being porous, is allowing water to seep through. I expect also that you
are using standard silicone which releases acetic acid (vinegar smell?)
which will further exacerbate the rust corrosion.


Good point about the rust, that's just the sort of obvious thing I was
missing. The silicone sealer isn't the 'vinegar' sort (as far as I
can see or smell) it's from a tube of RS stuff left over from work.
Very thick, very sticky, looks almost like heatsink compound.

You could try killing the rust with jenolite or similar phosphoric acid
based stuff, allow to dry and then paint with multiple layers of cellulose
over a zinc or epoxy based primer.
Once this is really hardened, refit the element with electronic grade
silicone (no acetic acid from this type). Don't bolt up really tight for
a day to allow the silicone to form a seal before you squeeze it all out.
The next day, finally tighten.


That might work. The slot should be big enough to get an inspection
mirror in, so I could even check and paint the interior edge.

Make sure every trace of water is removed before you start.

Good point, I've been blowing into it with a fan heater.


As an alternative to the paint treatment, after the jenolite stage,
annoint the surfaces with full strength araldite (not the rapid stuff !!)
to seal over the rust and well onto the enamel. If it is cold and the
surface won't smooth nicely, warm GENTLY with a hair dryer. Don't go too
mad with the heat otherwise is will all run away. Leave 24 hours plus
before using silcone to refit the element as above.

This might be plan 'B', I'd be worried about hearing a 'crack' just as
I decide to nip the nut up a tiny bit more.......


hth

Bob


Thanks, that was just the sort of thing I was looking for.

Cheers,

Phil Young