Mineral wool insulation in an atticSlag Wool Building Insulation Properties
Man-made slag-wool insulation health effects

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Slag wool or mineral wool insulation health effects & asbestos content.

This slag wool insulation article series illustrates and describes mineral wool or "rock wool" and slag wool insulation materials and addresses questions of health effects of exposure to slag wool or slag wool dust and debris.

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Slag Used in Rock Wool / Mineral Wool Insulation Products: Health Effects?

Mineral wool insulation in an atticWhat is Slag Wool Insulation?

Slag wool is a manmade vitreous fiber made by spinning slag into insulating fibers. Some rockwool producers use nearly pure recycled steel slag.

Mineral wool insulation, developed in the 1850's, patented in 1875 in the U.S. and this material, also called rock wool or in some texts slag wool insulation remained in popular use in the U.S. up to the 1950's, and is still in use today (2008) in some new construction, in manufactured housing, and in special applications such as the insulation of low-slope roofed cathedral ceilings and scissors-truss roofs.

For most purposes, mineral wool, stone wool, slag wool, and rock wool are synonyms, though some of these terms such as "rockwool" may be trademarked by some companies.

Reader Question: Are there any companies that produce slag based insulation in the USA?

12 Feb 2015 Anonymous (a slag recycler) said:

Are there any companies that produce slag based insulation in the USA? I cant believe this country.Here is a recycled product that from everything i have read is fire proof, better r-value, and doesn't make you itch like fiberglass but we won't make it.Why?Are there no business minded people left in this country?You would think even the tree huggers and the government would think a recycled,fireproof insulation would meet there approval.

I recycle slag and can't understand why I am having such a hard time selling a recycled product even after I take out all the metals,screen and produce a quality product that even passes penn dot specks. It compacts better,in most cases is harder and you didn't have to rape mother earth to get it. Not forgetting the stone quarries can still make concrete with there stone so we won't have to import other countries concrete.

What's that worth? Less going into landfills,less imports, less holes dug in mother earth and better, safer insulation. the fuel savings not having to ship insulation and concrete across oceans and dig unnecessary holes should pay for the fuel needed to make the rock wool insulation. I don't know but i think we could use the jobs here and maybe export a product ourselves. What a concept. No one cleans the air from smokestacks like the USA and last I looked there isn't a wall to stop the smoke between here and China, so lets get real. Please tell me your opinion and let me know if anyone knows of a company that is or might be interested in producing slag wool in the usa.

Reply: Research on health effects of production or use of mineral wool / slag wool products

Slag products are still in active discussion regarding their use in insulating products both in the U.S. and in other countries as you can read at

Depending on the actual slab you are suggesting be used to produce insulation (which certainly has been done elsewhere). These references shed some light on present and previous health effects of exposure to slag or mineral wool or "rockwool" particles and fibers.

Question: Some mineral wool insulation is falling into my bedroom from a small hole. Is this harmful?

I recently had a carpenter in my older home (built 1981) fixing an issue in the attic and much to my disappointment made a hole in the attic and all of this (i'm guessing rockwool insulation) came tumbling down in my master bedroom covering everything. Some of the things it landed on are non washable. Is this insulation harmful to me and my family's health???? Please respond ASAP major clean up in the process. - Geniah Melendez

Reply: Generally not in small amounts; It depends ...

Rockwool is a mineral fiber product, and of course it could contain dust from the attic: insects, debris, etc. If you HEPA vacuum up the dust and launder what can be laundered or dry cleaned you should be OK. It's not radioactive and it's not asbestos. Heroic measures should not be needed.

Additional reader comment from Debra Monte:

You should be more concerned with dust from the walls and ceilings, which most likely contained lead paint. Get your blood work done and get tested for lead content in your blood. The likelihood of asbestos in home insulation is very low. However, there may have been a combination of insulation types, such as rock wool/mineral and vermiculite. Vermiculite that was mined in Libby, Montana does contain a small amount of asbestos.


At the article titled VERMICULITE INSULATION (link at the "More Reading" links at the bottom of this article ) you will find US EPA and other authoritative sources that help separate opinion from fact about asbestos and other environmental hazards.

I agree that lead hazards are ubiquitous in older homes in many areas and are an important concern. We have published extensive information about lead hazards in buildings and in water supplies, found through our page top and page bottom major topical link ENVIRONMENT

Watch out: also be sure to read ASBESTOS IN MINERAL WOOL / STONE WOOL in this article series.

Question: does modern rock wool still contain formaldehyde?

9/11/154 Darlene said:

Does today's rock wool still have formaldehyde? I have what appears to be rock wool insulation in an add-on room of my old farm house, but it has a paper like on the outside and a foil like material on the inside. We have the walls open and want to insulate, but are unsure as what to do. Do we slash the foil and add more rock wool or tear out what we have and start fresh. We just want to do the right thing and tired of all the seconds guesses at the big box stores.



Rock wool is a mineral fiber inslulation material that does not now and never did include formaldehyde.

Article Series Contents


Continue reading at MINERAL WOOL by MICROSCOPE or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see BALSAM WOOL BATT INSULATION - a cellulose product, not a mineral fiber



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