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Firescale and blasting


Hello Lisa!

Saw your post on Orchid. Glad you like your blast unit. I have a
compressor (Sears, noisy, love that hummm!) that I intend to
hard-line also. I bought 1/2 inch copper to do it. A friend told me I
should just use PVC. When you decide let me know. It is a rainy day

Anyhow on the firescale here is a solution to alleviate it, and how
to deal with it after it occurs.

Instead of using Boric acid and alcohol try this recipe:

1 cup? - 2 parts – boric acid 1 cup? - 2 parts

  • borax (yes, 20 mule team borax) 1/2 cup? - 1

part – tri-sodium phosphate (TSP - you will find it in the paint
stores, they use it to clean surfaces prior to painting-good stuff)

I learned of this concoction several years ago, and have hardly had
firescale to deal with since! It is truly remarkable! Mix all three
ingredients (by weight) in a bowl. Put in a pan and add water till it
can be stirred and is the consistency of salad oil. Bring to a boil.
The solution will then be clear. Simmer for a while to evaporate the
water out. You want to return it to powder state. If I am in a hurry
I will pour it on a platter and put it in the microwave. No
accidents, won’t be a problem. You can just put it up somewhere and
let it evaporate over a few days, to a powder. You will end up with
dry white moon surface looking stuff. Scrape it all back into a bowl
and pulverize. It is easy. Mix with alcohol and use like you normally
would. However add these steps you need to eliminate firescale: coat
and fire twice. Torch the piece to a temp. just before the coating
starts to glaze. Let cool, dip and fire again. No need for flux.
Fluxing does help, but will increase the chance for firescale. If you
must flux, do what you can to keep the flux from bleeding around the
seam. Do your soldering with a reducing or neutral flame, if
possible. Pickle and there should be no firescale at all! If there
is, use a steel side brush, 3/4" (for all metals, the brass ones’
don’t work as well) wet, with baking soda. If the light scratches are
undesirable, try 3/4’ polishing side brush. Use it wet with soda. If
you have a bad case of firescale, and go to blasting, you will find
it is still there no matter how much you blast. Better to try to
reduce firescale in the first place. Man, that took awhile! Good luck!