Rockwool insulation

[Sugarsnow]

Does anyone have experience using rockwool insulation under firebricks in a arch? If so did it work?

[Evets]

Yes, I've used it with good results for a few years. Before I used it I held a propane torch on to how durable it was. The torch didn't hurt it at all. There may be better insulators but it works fine for me.

[Bricklayer]

I used Roxul IS board in mine. I think it's 1.5". And then bricked over it. I didn't brick all the way to the top. I stayed down from the rails 3" and cut the brick on a sharp angle to get the flame as close to the edge of the pan as possible.
Then before I bricked I covered the exposed Roxul with 1" ceramic blanket. I can hold my hand on the side of the arch when it's rocking and it's warm but not hot.
Beyond the firebox I used roxul and covered it with 1" ceramic blanket.
I had a mouse get in last year and build a nest so I had to replace the ceramic blanket. In the back section. The roxul looked like the day I put it in after 2 seasons using it.
If you can get the Roxul IS board. It is pretty ridgid and the brick will sit against it nicely.

[Millsy]

Hey Bricklayer, Where do you purchase the Roxul IS board?

[Bricklayer]

Home Depot. It looks like Roxul is now called Rockwool as a brand name. Wasn't aware of the name change. Just make sure it's thecomfort batt IS board. I think comfortbatt 80 is a little flimsy. But should be in the same isle.
https://www.homedepot.ca/en/home/p.comfortbatt-80.1000737930.html

[brocken]

do you add any supports through the rockwool to help support the bricks, seem like you don't want to compress the insulation or you will loose R value.

[Bricklayer]

The IS board is ridgid. So no. If you use a full bed of fire clay ( high heat cement) and full head joints it will be very solid. If your door doesn't take up the whole front of your firebox and there is room for a corner then that will help tie in the sides. But if not it will still be pretty sturdy once dry. If you run steel through the firebrick to tie it in it will expand and contract like steel does and crack the joints.
A little movement is normal.