What Exactly is Mineral Wool?
The origins of mineral wool go quite far back in history. The first slag wool (a by-product of metal smelting) was made in 1840 in Wales, but at the time no one knew how to use it. In 1870 an American patented a process to keep the wool strands together and it was commercially produced a year later in Germany. Fast forward to 1936 when a company called Spun Rock Wools Limited began manufacturing wool in pads by heating dolomite shale and pouring it onto a “spinner.”
History notes that the first mineral wool manufacturing wasn’t commercially feasible until the 1950s, and more forms of mineral wool were created in the 1970s and 1980s.
Beyond Group uses a mineral wool brand called Rock Wool, as it is made from stone wool which is a combination of basalt rock and recycled slag from steel. Slag is the solid waste created in the process of making steel and is mainly made up of calcium, iron, silicon, magnesium, and other elements.
The rock and slag are melted down and spun into fibers to make the battsof RockWool.
RockWool is noncombustible and fire resistant; it works to keep the firefrom spreading and will not emit toxic smoke even when exposed to flames.
It is also water repellent which helps reduce moisture collection, and it will not expand and contract with temperature changes.
RockWool is a widely available product, but due to high demand there is sometimes a shortage.
How Does Mineral Wool Compare to Spray Foam?
Let’s get right down to the numbers first. Installing mineral wool is much like the batt and poly system and costs about $2.80 per square foot versus$4.50 for spray foam.
Other differences include air seal, soundproofing, moisture repellence, and R-value (the measurement of how well it keeps the heat in).
RockWool is also easier to remove and replace if work is needed on plumbing, electrical or mechanical issues. Whereas foam tends to bury those services.
The main difference is the air seal. Spray foam is very airtight. Once applied, it will seal all the gaps and cracks in your home. Mineral wool, while thicker than spray foam generally, will still let more air flow through, even with a properly installed vapor barrier.
When it comes to soundproofing, mineral wool is much better than foam. Open-cell foam is a good sound barrier, but compared to wool, foam has nothing on it. That said, open-cell foam is rarely used in our colder climate as it doesn't perform as well as closed-cell foam. However, we can use it for hard-to-reach areas in a pinch.
Mineral wool is water repellent and still requires a vapor barrier. Whereas spray foam has the vapor barrier built in, so it isa much better moisture repellent material.
Mineral wool has an R-value of R4 per inch. If you completely fill the space between your drywall and your exterior wall, you will need 5.5 inches of wool to achieve R22, but you only need three and a half inches of foam to get the same R-value.
Looking at it from a price perspective, to get R22 in a 2x6 above grade wall cavity, the cost for using RockWool will be $3.70 per square foot, whereas spray foam would be $5.50 per square foot.
