What to do with dried out braze paste or paste separation?

Most operators have probably experienced braze paste, whether supplied pre-mixed, or made up on site which has either separated or has dried out and hardened. There's normally a couple of reasons for this but also, more importantly, a few simple remedies to resolve the issues quickly and simply on site.

Automated Paste Dispenser

The vast majority of manufacturer produced paste will remain stable for many months, if not longer, but occasionally a batch may separate earlier than expected. This is not necessarily due to any manufacturing flaw but occasionally due to the complexities involved in the chemistry between the alloy powder ions and the gel-binder you will find the the paste separating leaving a thick layer of liquid on the top of the paste.

The simple solution to this issue is to simply re-mix the paste manually. The alloy in the paste is still perfectly good to use, it is simply that the binder is struggling to hold the suspension. If in a cartridge remove the stopper and use a spatula or similar to agitate the paste to remix it. Do not be tempted to pour the liquid away! The liquid is essential to maintain the viscosity of the paste.

Typically we will manufacture our pastes to between 85-87.5% alloy powder by weight. When pastes are made up on sites be mindful of the ratio your operators are mixing to, we have seen 60/40 ratios and more, too much binder in your mix can cause issues on the braze cycle and thins your paste.

If paste is left out exposed to the atmosphere it will naturally dry and harden. If your operator has left the lid open on on a large tub of paste you will be reluctant to throw it all away.

The easiest way to reformulate your paste is to simply add more binder gel back into the mix. If you don't have any binder gel available you can use water (de-ionised is better) but just be mindful it will affect how your paste behaves when applying it - but it will save you having to throw a lot of perfectly good paste away.

We supply our Grade-ST binder gel in 500g tubs, why not keep a few in storage just in case?

Vitta-Braz Grade-ST Binder Gel

In summary the filler metals in any hardened or separate paste will virtually always still be good to use. Simply remixing your paste that has separated or adding more binder gel to a hardened paste will, in the vast majority of instances, make your paste good to use again.