Slag on firebrick?

My wife scored a beautiful old coal stove on freecycle, and I spent 8 months or so restoring it.



It's been heating our house delightfully for two years, but I notice that over time, the inside is building up a crust of slag on the firebrick. It seems quite resistant to being chipped off, and I fear that if I go at it too enthusiastically I'll damage the firebrick beyond repair. This is an oldie so I don't know if the brick can be replaced.

Any thoughts would be welcome, and thanks for your time.

Can you get in there with a 4" grinder? If so, you could use a diamond blade to " scrape" or cut off the slag without beating on the bricks...

When you shut down in the spring you can fabricate new bricks from readily available refractory materials.

http://www.nockrefractories.com

Some of the clinker slag is relatively soft and you can file it off with a carpenters rasp file.

Some is iron oxide and very hard. That is where a grinder will need to be used.

There is one method that worked for me, but you have to be very careful and go slowly. By carefully tapping with an old carpenter's chisel and a small hammer I was able to get off a lot of the clinker slag on the 100+ year old firebricks of my range's firebox. But, you can't angle the chisel into the bricks or they will crack. You have to use the chisel almost parallel to the brick surface so the force of the light blows is being absorbed along the brick's length, where it's strongest, and not crosswise to it's thickness, where it's weakest. And you have to work the chisel in around the edges of the highest points, not just try to cut them off from one direction.


In a few areas the slag had eaten into the brick face and took out some brick with them. I filled those areas flush and smooth with Hercules furnace cement from Lowes. Brush clean and then wet the bricks first so that you get a good bond with the cement. Let dry 24 hours.

Paul

Many thanks for taking the time to respond!