If the first layer of mineral wool comes to the top of the joists, put the second layer at a right angle so it covers the joists.

Don't skimp on safety precautions. I've found it a very irritating material to work with.

Much easier than using batts, try blown mineral wool (or cellulose).

Worthy, I have read warnings about using mineral wool but I was at home depot and pulled a bit of material out of an open bag (sml amt) , and my hands were fine. The material was soft and it didn't itch like fiberglass. What precautions should I be aware of besides the usual respirator/mask, eye and clothing protection. It appears to be benign compared to the fiberglass.

My house was built in 1947 and recently found out some old tile in my basement has asbestos. I panicked and looked at the insulation in my attic. It is brown loose and fluffy with blue & red soft flecks in it. With an educated guess, what do you think it may be? Cellulose, rock wool?

What precautions should I be aware of besides the usual respirator/mask, eye and clothing protection[?]

That's it.

chappy27

Modern cellulose insulation wasn't used until the 1950s, so it's likely you have some sort of rockwool with mould growth or its residue. The mould lives on the dust in the wool, not the material itself.

According to Inspectapedia, "Mineral wool insulation, slag wool insulation, and 'rock wool' insulation would not be expected to contain asbestos fibers - We have been unable to find reports indicating otherwise."