One of my favorite insulations on the market today is mineral wool otherwise known as Rock Wool. Even though it lags in use compared to the more popular fiberglass insulation that most people are familiar with it is, in my humble opinion one of the best insulations available today.
You may be wondering why you should consider this new insulation compared to the standard fiberglass you’ve known for years. I’ve given a much more detailed write up on mineral wool’s advantages in this previous post, but I’ll give you the main points below.
Mineral Wool Advantages
- Higher R-value than fiberglass (R-15 vs R-13 in a 2×4 wall)
- Hydrophobic (won’t absorb water)
- Less sagging than fiberglass
- Easier installation for DIYers
- Itch-free product
- Less palatable to critters
With all the advantages above it was a no brainer when I was remodeling my bathroom this year to install mineral wool on the exterior walls. It was also the perfect time to show you howe to install it since the installation, while easier in my opinion is considerably different than fiberglass insulation. Let me show you what I’m talking about.
How To Install Mineral Wool
Mineral wool does not come in faced batts like fiberglass. There is not a faced version so if you need a vapor barrier then you’ll have to install one separately.
The main difference when installing mineral wool is the cutting process. To cut fiberglass insulation you just need a razor knife and a piece of plywood or drywall to compress it and slice it to size. For mineral wool you need to use a stone wool knife or a serrated bread knife will work just as well.
Mineral wool is much thicker and dense than fiberglass and can’t be compressed in the same ways which, I feel, makes the installation more foolproof. The biggest issue with DIYers installing fiberglass is that they compress it around obstructions or it sags in the cavity. This is not something that happens with mineral wool since it won’t compress the same way.
Step #1 Cut to Size
The mineral wool needs to be cut to length for the stud bay using the stone wool knife making sure to cut it tight. Don’t leave any gaps. Lay the mineral wool on the floor and with a sawing action cut the insulation to size both length and width if necessary due to unusual stud spacing.
Step #2 Cut Out Obstructions
Next, place the batt in the bay and mark any obstructions like electrical boxes, plumbing, wire, etc. You’ll need to cut each of these out like a puzzle piece using that same knife.
When cutting for wire simply cut a slit in the mineral wool and the wire will slot right in. For pipes a reverse shaped V cut works best to give the pipe room to bed properly within the insulation. Make sure to cut everything tight and not leave any gaps to have the most effective insulation coverage.
Be especially mindful on exterior walls around plumbing lines to ensure that the insulation goes to the exterior of the pipes to prevent freezing in winter. Don’t insulate just the interior side of the pipe as a shortcut.
Step #3 Press into Place
Unlike fiberglass, this is designed to be simply pressed into the wall with a tight fit. There is no stapling needed. If you are installing on a ceiling then installing strapping to keep the insulation in place until drywall is installed works best. Typically these straps are unnecessary because it’s designed to fit standard stud widths very tightly.
That’s it! You’ve now got a hydrophobic, R-value dense insulation installed and ready for drywalling or plastering. No worries about sagging or even wetting since mineral wool is dense, and inert. You’ve successfully avoided mold and critters too.
If you haven’t considered mineral wool insulation for your house it may be time to give it a look.
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I love old houses, working with my hands, and teaching others the excitment of doing it yourself! Everything is teachable if you only give it the chance.