Barrier flux

Can anyone share with a simple recipe for making “barrier flux” with
boric acid?

Linda Gasparini

Can anyone share with a simple recipe for making "barrier flux"
with boric acid? 

Just use plenty of it!! for heavens sake!! Experiment as well on base
metal to develop your technique, then use it on the expensive

Thanks for the suggestion, but I still don’t have the recipe! How
much boric acid should I use with denatured alcohol, for instance?

Linda in central FL

Linda –

For many of us there is no exact recipe. Take the tightly closeable
container you will keep on your bench. Fill it about 2/3 to 3/4 with
alcohol. Stir in as much boric acid as will stay in suspension; never
mind if it wants to precipitate out a little. To use, stir the
mixture to increase the solids in suspension. Dip your piece in the
mixture, and immediately set on fire. This will set the boric acid on
the surface much better than just letting it dry. It’s then ready for
your next step. Just be sure you close the dipping container before
lighting off the alcohol!

Mix up so its a creamy paste that sticks all over the item to be
protected. If its too runny it will fall off. if to thick it wont
cover evenly. try it out on some scrap first. youll soon find out
what works for you. there isnt an actual recipie as such.

a note to someone eles’s post: you must use denatured alcohol- not
isopropyl alcohol (rubbing alcohol), with the boric acid. You are
after a firescale preventative and flux in one right?.. so add the
boric acid into a glass or other container that is acid proof ( lids
on mason jars with an enamel coating and rubber seal work but must
be changed after a while as the alcohol dissolves the rubber and can
rust the lid eventually- many people can’t figure out where iron
contamination comes from - in some cases its the iron oxide(s) from
something as overlooked as the jar lid your Pripp’s is mixed in (some
call the alcohol and boric mixture “Pripp’s Flux” - a blush is left
on silver after pickling giving it a pinkish colour, or some other
contamination related reaction) adding the boric acid into the
alcohol until you have a saturated mixture about the thickness of
cream. Don’t make more than you think you need for a three month or
whatever your production dictates) supply. Each time you go to use
(it you can shake the jar or stir well. It will seperate - no problem
there, just remix well…

I noticed someone else said their recommendation was to make it
thick and use plenty, while someone else said to set it on fire- both
of those aren’t exactly the objective or good habits- setting it on
fire… You really want to dry between applications if you are
building a coating as opposed to just a hit and run solder operation-
so use the torch to dry it, don’t burn it off!

Another good option is 4S labs Cupronil (no affiliation, etc. i just
trust the stuff and have used it for years !). It’s a superior flux
and firescale preventative spray that is reasonably priced and
readily available from most vendors - i prefer it far more than
firescoff: for one thing it sprays on better and building up layers is
easier, the “ceramic” ( their big selling point) is a crystalline
powder that can seperate out in cold weather ( but doen’t affect the
overall product if you reconstitute it- ) The manufacturere also
claims that pickling isn’t needed, and one can do multiple solders
from a single application… i haven’t found that to be the case with
the product at all… some like it, some don’t and as far as I know
it’s gone through at least 3 reformulations

“improvements”…their MSDS had to be revised and reworded (at first
it said it was non-toxic, until you looked at the original MSDS that
said it was toxic to aquatic life- if that’s the case what was the
toxic agent (flourides? which aren’t supposed to be in it???) So i
don’t trust the stuff and don’t think it’s as effective as the
marketing would have you believe… As for using " lots of flux", for
one thing use the *least *amount to be able to see your work, and to
see the flow point of whatever flux you use ( some get clear when
soldering temp is reached), you want the solder to flow on clean
metal, with enough flux to “guide” the flow…using alot, particularly
a paste type, doesn’t help it flow better and in some operations,
like multiple soldering you just create a mess with burned out flux
on top of another application of flux and so on depending on what
solders are needed ( working hard to easy in multiple soldering
operations) if you don’t pickle between each solder (it really isn’t
necessary to pickle after each solder when, for instance you are
closing a bezel and setting it on a backing plate…so the less mess,
the easier it is to keep the work clean enough for the solder to flow
completely and making a good bond. hope this helps, rer

I would suggest searching the archives for Prips flux and consider
that route. It is a little more trouble to make (but not much) when
compared to a boric acid suspension in alcohol, but is a heck of a
lot safer. It might be a tad more time consuming to use as you heat
the piece and mist it on. If you don’t use it a lot one of the
[expensive] commercial products works well. I’ve used the boric acid
suspension, Prips and Fire-Scoff and they all give good results, but
the Prips and Fire-Scoff seem to hold up better in repeated
operations for me. Milage varies by customer I guess… Everyone has
a favorite.