Rock wool?

60+ year old house. Original faced wall insulation.
Is this faced rock wool, or dirty glass?


By the colour and if original, I’d say “rock wool”

gray black
Rock Wool…
better than fiberglass…

Thanks, guys. I thought so, but I’ve had no previous experience with it.


Learn how to do it the easy way.
Mineral wool/fiberglass type material.:slight_smile:

It’s not Perlite. :smiley: :stuck_out_tongue:


rock wool
no comparison


I tend to rate them as near equals for R value & installation except when it comes to cost…rockwool batts are more expensive than fiberglass batts here!!

With higher R values (up to R50 in attics) in todays’ much more efficient homes, the extra weight of the heavier blown rockwool on flat attic surfaces may require 5/8" drywall or thicker on the ceiling.

For example: 1 brand of rock wool I looked up had a weight or 2.68 lbs/sq ft for R34. Cellulose is 1.23 lbs/sq ft for the same R value.

pic in first post looks like perlite?

all insulation is inadequate at best to the claimed ® values.
Installation methods may vary…

The easy way to tell is to take a hot shower after you get home from the inspection. If you start itching so bad you can’t write up the report, it was fiberglass.

Perhaps a “tongue-in-cheek” reference to this thread…

BTW… post #13 is still awaiting your reply. :stuck_out_tongue:

I agree with you hypothesis on the 5/8 wallboard.
Imagine the weight the the RW will have if it carries moisture.
Q: What is rockwool?
A: Rockwool is spun mineral wool fiber. Various “rock” components, with a heavy dose of silicon oxides are melted at high temperature and fibers are formed as molten material is passed by a series of “spinners.” The finished product which is “bonded” via proprietary resins, is inert, meaning it has no cation exchange capacity. Approximately 97% v/v/ is air space. Bonded products (plugs, blocks and slabs) also contain a wetting agent, which may (absorbent) or may not (repellant) be present in granulated (also called flock) rockwool.