"David W.E. Roberts" wrote:
"Rick Hughes" wrote...
WIPE off any external flux while still hot. This is easy
to do but plumbers never seem to bother. It eventually
makes a green mess if you leave it.

I got bollocked by a Corgi regd guy for wiping the joint -
he was adamant that this was a fail on a trade test if you
did that (been a heating engineer for 50+ years) His reasons
were that the solder ring should form and you should leave
it at that, if youy wipe it yopu stand the chance of wiping
impurities into the joint.

He is right that you must not wipe off the joing while it is
hot, but for the wrong reason! There are at least two valid
reasons: 1) When you wipe the join you may mechanically
disturb it as the solder sets - this may cause the equivalent
of a "dry joint" and be subject to leakage; 2) Fast cooling,
say when you wipe with a damp cloth, can lead to the formation
of "large" crystals in the solder, and even cause a shattering
effect on the solder in the joint, which may be mechanically
reasonable in appearance, but be in fact porous. You can test
both these (rather extremely, but it will show the effects,
quite easily. For the first, couple two convenient lengths of
15mm tube, hold each end of the pipework with pliers, and
wiggle the tubes about constantly while the solder solidifies.
Inspect. For the second case, join two short pieces of tube,
and before the solder solidifies drop the whole thing into a
pail of cold water. Inspect.


Wipe it off when cold?

That's it - as mentioned elsewhere modern fluxes are water-
soluble (which is why you shouldn't drink from new pipework,
the water in it will contain dissolved flux for a while), so
a damp rag will clean off the flux - for "fluxite" and other
types mechanical cleaning with steel wool is the way to go.
--



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