Can dried up silver solder flux be "reactivated"?

Vladymere gr · Sep 3, 2009

Fellows,

I occasionaly have the need to do some silver soldering but not very often. My bottle of paste flux has dried up leaving a hard "rock" inside. Can I reactivate or restore this material to a past by adding water to it an letting it stand for a day or two and then mixing and repeating this process until it is a paste again? Isn't silver solder flux just a paste of borax?

Thanks people,

Vlad

Himself · Sep 3, 2009

I do it. Add water and pulverize with a piece of scrap stock. I use this to silver solder carbide chunks onto steel sticks for use turning at home only. It seems to work just fine. No failures yet. What do you have to lose, if a customer was involved I would buy new flux.
All the best.

Bruce Griffing · Sep 3, 2009

The white flux can be renewed with just water. It is just borax and water anyway. Don't know about black flux - but it is worth a try.

Some folks mix the borax with alcohol - it does burn when heating the joint, but does not make the flux run. So alcohol is another thing to try.

Ray Behner · Sep 3, 2009

Vladymere gr said:
Fellows,

I occasionaly have the need to do some silver soldering but not very often. My bottle of paste flux has dried up leaving a hard "rock" inside. Can I reactivate or restore this material to a past by adding water to it an letting it stand for a day or two and then mixing and repeating this process until it is a paste again? Isn't silver solder flux just a paste of borax?

Thanks people,

Vlad

Vlad,

Maybe you're not supposed to, but I've done it for years without a problem. I put a little water in it and mix again.

Ray

Vladymere gr · Sep 3, 2009

Thank you gentlemen. Water will be added.

Vlad

Don_Hartman · Sep 3, 2009

I have done the same to the high temp black flux also.

Don

surplusjohn · Sep 3, 2009

I thought it came that way..

adama · Sep 3, 2009

As a kid we use to have a small jam jar of the stuff, just water and mix up every time we needed it. That stuff must have been remixed hundreds if not thousands of times and still worked just fine.

Armenius · Sep 3, 2009

For serious silver soldering that involves lap joints of some dimension I use distilled water to make paste flux that has hardened... Ask me why.

Arminius

Exptec · Sep 4, 2009

I have done it with the black boron type flux used for silver soldering stainless steel. I used a double boiler arrangement to heat the flux and water mixture. The heat really helps getting smooth lump-free or grit-free results.

Exp Tec
DBA
Experimental Technique

tomwalz · Sep 4, 2009

White brazing flux is potassium salts of Boron and Fluorine. Black flux is the same with extra Boron added. It is mixed with water. If the water evaporates out at room temperature it works to just be remixed with a little water. If it has been heated over 500 F and has dried out it has lost some of its effectiveness.

Karl_H · Jun 24, 2020

Armenius said:
For serious silver soldering that involves lap joints of some dimension I use distilled water to make paste flux that has hardened... Ask me why.

Arminius,

All right - almost 11 years later - WHY ?

michiganbuck · Jun 24, 2020

We painted fiux on both side of a shaped braze strip often to let it dry hard, the we heated to a mold cherry red to let the braze ment, mover the cardide a little and set off to cool...with never any problem.

Often if not always we pit a tiny piece if silver in to make the braze flow better.

Flux seemed to melt and get glass hard..It wasrough on grinding wheel so we put all the TCT bits in abucke of wter and boiled them to melt off the flux glass...they cane out like gun blue and the customers though that was a plus.

mike44 · Jun 24, 2020

Like the rest of the posts, add small amount of water. I break up the large chunks with a screw driver. Add some water, stir using a piece of wire from a clothes hanger. I bend the wire to a T shape ,cut the straight part about 4" long .Install the wire in a drill press. Slide container under the wire. Turn on DP and it quickly becomes a paste again .
mike

sfriedberg · Jun 24, 2020

I keep a cheap kitchen mortar and pestle in the shop on the same shelf as the brazing gear, precisely to grind rock-hard chunks of old flux into something usable.

jim rozen · Jun 25, 2020

Other trick: if you know it won't be used for a while, fill the container up with extra water when you put it away.

WizardOfBoz · Jun 26, 2020

Armenius said:
For serious silver soldering that involves lap joints of some dimension I use distilled water to make paste flux that has hardened... Ask me why.

Arminius

I was just thinking that "Boy, it would be best to use distilled water, to avoid contaminating the flux with the stuff dissolved in tap water". Don't know how calcium, magnesium, sodium and potassium affect the wetting action of borax, but if you repeatedly use tap water you may end up with less effective flux.

May not be an issue, but for less than a buck a gallon, I'd used distilled water.

richard newman · Jun 27, 2020

bosleyjr said:
May not be an issue, but for less than a buck a gallon, I'd used distilled water.

I agree. I keep a gallon around to reconstitute or thin anything that might be sensitive to whatever is in our water.

And a Britta filter for drinking the stuff

Can dried up silver solder flux be "reactivated"?

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