Reddit reviews Rutland FSC16 Gray Chimney Sweep Furnace Cement, 1 Pint

I wouldn't use anything with aluminum in it in any quantity at forge temps, even if it's refractory lined. Best cast scenario, it leaks molten aluminum. I don't like that best case scenario so I certainly don't like the worst.

If you live somewhere cold enough to necessitate actual wood stoves, you might check a fireplace repair or supply company or the fireplace section of your hardware stores for a product called furnace cement; if you can't find it locally, hopefully you can order it online, word is that this "Chimney Sweep" type is the highest temperature rating but any of them should work fine, especially if you proceed to line it. 4 parts perlite to 1 part furnace cement, for a coffee can forge a 1/2 pint of furnace cement should be more than enough. The cement is sticky and hard to work, it's a lot easier if you mix it with 1/8 the volume of cement in water. Here's a workthrough for a crucible furnace partially made with the perlite/furnace cement refractory. If you can order online though, there's plenty of pure sodium silicate to be found. I hope some of this helps.

If you're dead set on sodium silicate, Rutland brand cement floor sealer is apparently 100% pure Na2SiO3, and hopefully you can find this locally. If absolute worst comes to worst, you can mix those little silica gel dessicant beads (or crush up some quartz crystals) and mix them with lye (sodium hydroxide drain cleaner). Good luck, let us know how it goes!

EDIT: after doing some reading I definitely wouldn't recommend going the sodium silicate route; with a melting temp of 1,200°F (the very low end of typical working temps for forges, steel would barely be at a dull red before your forge started to liquefy. I'd love to be proven wrong, though!) Worst case scenario now is just wasted money and knowledge gained.