This article describes asbestos millboard or asbestos wallboard, an asbestos cement board product usually quite hard, that was heat and moisture resistant, widely used across a range of products described in this article series as well as a barrier on ceilings and walls.

Page top photo: asbestos cement millboard in a photo contributed by an InspectApedia.com reader.

Asbestos Millboard: Identification, Properties, History, Hazards

Asbestos millboard is a cementious product, usually about 1/4" thick or less, that was produced in sheets and used for fire barriers or moisture and weather resistant sheet products in other applications.

Asbestos millboard (photo above) used for stoves and heaters, in garages, as fireproof wallboard, as thick gaskets, as washers in electrical applications, stove mats, safes, motion picture booths, automobile hoods and a longer list we'll give below.

The material is quite similar to cement asbestos roof shingles and siding, and was produced in sheets of varying thickness (typically 1/8"- 1/4") and dimension depending on its intended use.

Asbestos millboard was used as a fire barrier behind and over and around wood stoves, coal stoves, & heating appliances in buildings up to 1978. It was also used in some locations where a moisture-resistant building material was desired.

Asbestos cement board products were very widely used as a larger form than asbestos cement shingle roofing or siding, and were found buildings, appliances, vehicles (cars, trucks, buses, streetcars, train cars, rocket parts, and in a myriad of other locations.

Asbestos fibers were a significant component of asbestos millboard (a cementious asbestos sheet product) sold in varying thicknesses and finishes, and often used as a fire barrier behind and over wood stoves, coal stoves, & heating appliances in buildings up to 1978 in the U.S. and much later in some other countries.

We have also found factory-built metal covered asbestos heat shields used a soft friable asbestos board product like the much thicker (> 1/2") tremolite asbestos board installed on the boiler room ceiling shown in our photo below.

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Watch out: the asbestos fireproofing board shown above and below is a softer, thicker and more-friable material than the thinner, harder asbestos cement millboard products used in other applications.

Uses of Asbestos Millboard / Wallboard Panels

• appliances including ovens, toasters, walk-in coolers, refrigerators, freezers
• automobile hoods, automobile fire-walls
• baking pads
• blackout or bombproof board
• boiler/furnace combustion chamber liners?
• brooder stoves bottoms
• ceiling "fireproofing" panels (see our Tremolite asbestos photo example of a softer asbestos board, above)
• deck under-sheeting
• doors, particularly metal clad doors (between outside metal and wood core)
• dry cleaning machines
• electric switch boxes
• elevator shaft control panels
• exterior sheathing for half-timbered home designs
• garage wall & ceiling coverings
• fire doors, predominantly Chrysotile asbestos
• fire door coverings between building & garage
• "fire proofing" over and near boilers, wood stoves & some coal stove installations
• fireproof wallboard in a wide range of construction applications
• garages, walls & ceilings
• garbage incinerators
• gaskets, plain and metallic including gaskets & washers where thick durable material was needed
• hot pads & trivets, usually metal-covered
• instrument mounting boards
• interior sheathing (refrigerator rooms)
• kilns, dry kilns
• lab table tops, cabinets
• mobile home floors
• motion picture booths
• ovens
• partitions
• radiant heat panels
• railroad cars, railway sleepers
• range hoods
• rockets
• roofing in shingle, sheet, corrugated panels
• safes
• ship construction
• siding in shingle, sheet, and other forms
• silos, grain & other
• storage building walls
• storage heaters
• stove mats
• stoves and heaters
• table pads and mats
• tank liners
• theatre set construction & some theatre fire barriers
• trailer floors
• washers in electrical apparatus
• washing machines
• welding shields
• woodstove internal section partitions

Many of the following examples of use of asbestos millboard appear and are illustrated in our separate

ASBESTOS PHOTO GUIDE to MATERIALS

Details about how asbestos cement board or millboard was produced are

at ASBESTOS MILLBOARD PRODUCTION

 

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2024-01-08 by InspectApedia DF (mod)

@Ash,

Please do let us know the results of your testing as that will help other readers as well.

On 2024-01-08 by Anonymous

@InspectApedia Publisher, thanks for the reply, reassuring. We’ll get it tested anyway to be sure but thought I’d see what it might be.

I agree that the worry is likely a worst hazard than potential airborne particles. But logic and anxiety don’t seem to speak to each other!

All the best.

On 2024-01-08 by InspectApedia Publisher - does this dimpled wallboard contain asbestos?

@Ash,

Asbestos millboard is a fiber cement product - it's rock-hard.

If your product isn't that hard it's not asbestos cement millboard.

In any event, in good condition and not being disturbed by demolition or other acts that create dust, intact materials like that in your photo are not likely to be a detectable airborne particle hazard - asbestos or other. The worry is a worse health hazard than the material.

Thanks for the question.

[Ed. note: this question was originally posted on our home page and moved to this relevant topic page.]

On 2024-01-08 by Ash

Hi,
As I see many other people are, I'm having major anxieties around possible presence of asbestos in our house. We have a converted loft space that my wife and I sleep in. Safe to say, the partition walls are of “mixed vintage”.

Amongst British Gypsum Gyproc Drywalls and “Royal Board” veneer boards from Sweden I’ve also found grey boards which are dimpled on the reverse (there’s wallpaper on the front).

I’m worried these are asbestos millboard. Any thoughts?

 

On 2023-04-28 by InspectApedia Publisher - identifying possible asbestos millboard used around a woodstove

@John B,

I'm not sure what question you wanted to pose. Basically you want to protect yourself from dust in any such demo project.

Certainly there were asbestos cement boards sometimes used as part of a fire shield. But not commonly several inches thick.

See

ASBESTOS MILLBOARD

ASBESTOS CEMENT PRODUCTS

and at our master collection of asbestos-material photos

ASBESTOS PHOTO GUIDE to MATERIALS 

we describe Asbestos Cement board used as a "fire proofing" over and near boilers and wood stoves - also called "cement wallboard" and "asbestos millboard".

Asbestone Corporation, a producer of asbestos cement board in the U.S. in the 1950's was purchased by National Gypsum in 1954. Ultimately Asbestone cement board products were one of National Gypsum's asbestos liability sources.

Asbestos millboard was used for stoves and heaters, in garages, as fireproof wallboard, as gaskets, as washers in electrical applications, stove mats, safes, motion picture booths, automobile hoods. Asbestos millboard is a cementious product that was produced in sheets and used for fire barriers and in other applications.

The material is quite similar to cement asbestos roof shingles and siding, and was produced in sheets of varying thickness (typically 1/8"- 1/4") and dimension depending on its intended use.

Asbestos millboard was used as a fire barrier behind and over and around wood stoves, coal stoves, & heating appliances in buildings up to 1978. It was also used in some locations where a moisture-resistant building material was desired.

I [DF] have found some thicker (> 1/2") or more asbestos board products, often not quite as hard as cement asbestos siding, used on ceilings and walls in boiler rooms.

Someone could have used such products under and on walls around a woodstove.

Your photo showing what looks like 4 layers of drywall was perhaps just that: ordinary drywall or at best, fire-rated drywall that someone thought would be safer in that greater thickness.

BTW that's not the whole fire safety story; for example nails can conduct heat into wood framing, also

see PYROLYSIS EXPLAINED

and see

FIRE CLEARANCES, WOOD COAL & PELLET STOVES 

On 2023-04-28 by John B - continued (mod)

@John B - continued,

It’s about 5/8ths thick. I do find it odd that drywall would be used as an underpayment for slate tile, but it’s also behind the concrete surround under a layer of thin set, fake concrete rock, and stucco screen.

I guess I just wanted a second set of eyes confirming it was just drywall, or saying “ whoa, it could be asbestos board”.

First pic I sent is under the slate tile, second two attached are the entire thing, and the edge behind one of the 2x4 trim boards I tore off.
Thanks again for taking a look.

On 2023-04-28 by John B - continued (mod)

I thought the was question was under the asbestos forum.
I wanted to know if there were any asbestos fire-boards that look like the pictured item.

I think it’s just drywall, but since it’s around a purpose built built wood stove surround, wanted to see if if it could possibly be asbestos. It’s a demo going on in a home we are living in.

On 2023-04-28 by John B (mod)

I am tearing out a wood stove surround from a house built in 1982 although the wood stove might have been added later.

I came across what looks like a thick drywall under the slate hearth, and behind the stuccoed rock facade walls. It is paper lined like drywall, and looks like gypsum. Any strong chance this is asbestos fire board?

Attached is a zoomed in picture is where I “dug” at it.

On 2022-01-11 by InspectApedia Com Moderator - asbestos-cement millboard in garage ceiling

@Katie,

That looks like asbestos-cement millboard.

If it is quite hard, it's that cementious product - not friable and thus not easily made into airborne dust (that would contain asbestos) as long as you're not chopping or grinding or making it into debris you've not exposed your family to a measurable level of hazardous dust.

You can reduce the concern by spray-painting the surface with any of the encapsulating sealants sold for that purpose.

See details at: ASBESTOS ENCAPSULANTS & SEALERS

On 2022-01-09 by Katie

My garage ceiling,which was installed in the 60's I believe, is a gray, friable material with a "textured" back. It never occurred to me when we bought the house that it might be asbestos. The owners before us, ripped some of it out to convert the 2 stall garage into a 1 stall.

Needless to say, it is broken up in places and even the original seams look "frayed." With the air drafts that move through the garage, it is certainly be disturbed. Is this likely to be asbestos or something else? I'm feeling quite anxious that I may have been exposing my family to this for years.

On 2019-05-16 by (mod) - Murale Gyproc Fire Protective wall board

Charmaine

Gyproc is a Saint Gobain Gyproc product line and name.

www.saint-gobain-gyproc.com

At ASBESTOS PRODUCING COMPANIES & TRUSTS

You will find a list of St Gobain products that contained asbestos

It would be helpful to know the country and city where your building is located, and the building age as those are key determinants in the asbestos -use question.

On 2019-05-16 by Charmaine

We have a product called Murale Gyproc Fire Protective wall board on some interior walls. Do you know if this product contains asbestos?
Thank you

On 2013-03-21 by (mod) - asbestos in firewall insulation of an older car

I don't have specific information, Blaine, but it would be no surprise to find asbestos in the firewall insulation. Asbestos was also included in some undercoating sprays.

On 2013-03-21 by Blaine

I'm currently restoring a 1968 Dodge Coronet. I was wondering if you have any info. on the carpet insulation, headliner insulation, or kickboard insulation being acm? Could you respond to fishingfam3@gmail.com?

 

 

 

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Continue reading at CEMENT ASBESTOS SHEET PRODUCTS, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• ASBESTOS CEMENT PRODUCTS
• ASBESTOS CEMENT SIDING
• ASBESTOS IDENTIFICATION IN BUILDINGS - home
• ASBESTOS LIST of PRODUCTS - home
• ASBESTOS PHOTO GUIDE to MATERIALS
• ASBESTOS ROOF MATERIALS
• CEMENT ASBESTOS SHEET PRODUCTS
• DOES THIS MATERIAL CONTAIN ASBESTOS? - 5 easy questions to tell if a BUILDING MATERIAL probably contains asbestos -
• FIRE CLEARANCES, WOOD COAL & PELLET STOVES

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ASBESTOS MILLBOARD at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to ASBESTOS HAZARDS

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