Rock Wool

[Uncle Tucker]

My new 2x6 Leader arch is finished and I just have to pick it up.
I have a lot of Rock Wool that I got on construction sites. It is used for fire proofing in commercial buildings. The pieces I have are 16”x48”x2” and are soft like insulation. I was planning to use this instead of arch board. If I take the sheets and pull them in halve so I have pieces 1” thick. Then I could put ½ firebricks in front of it in the firebox area. Then under the flue pan, I will leave just the rock wool 2” thick and cover all the metal.
I have a few questions.
Has anyone ever used rock wool for insulation?

I was going to brick the firebox to protect the insulation. If I use ½ bricks and mortared the joints in front of the rock wool, would that be strong enough to stand up to loading the fire wood?

Will the wool burn through, it is rated to 1900 degrees.
I asked Glen Goodrich if would stand up to the heat and he said it should.

[royalmaple]

I have some of the same stuff, I haven't used any, but I tell you what it looks and feels just like archboard. Which is used all the time. I don't know the temperature rating, but I know even the archboard really won't stand up if you dont have bricks in front of it.

I was going to use some, but forgot and bought arch board.

I'd be willing to bet it's super close to the same stuff.

[Russell Lampron]

Even with the Rock Wool or arch board you want to use full fire brick. There is a lot of heat generated in the firebox and you don't want to burn the outside of the arch.

Russ

[Uncle Tucker]

Ok I was thinking what if I covered the wool with blanket?

[RileySugarbush]

I used 1" rock wool behind full firebricks in my home built 2x6. The box was a good size such that the 1" insulation plus the width of the bricks were a tight fit, allowing me to dry fit them securely. The vertical side and back walls made it easy to fit all the bricks in without cutting. I'd like to take credit for good planning, but I just got lucky. Regardless, the insulation was sufficient, with the outside of the box getting pretty warm but not dangerously hot. it's got one good season on it and the bricks did not shift at all.

As far as I can tell, 1" rock wool and arch board are the same thing.