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Mineral wool with cellulose inclusions from a 2002 home  (C) Daniel FriedmanMineral Wool Building Insulation Under the Microscope Mineral wool: Rock or Stone Wool or Slag Wool Compared With Fiberglass Insulation

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Rock wool or mineral wool insulation examined under the light microscope.

Microscopic examination & identification of mineral wool, slag wool also commonly referred to as rock wool used for building insulation. Photographs of mineral wool under the microscope.

This article describes and illustrates the microscopic properties of mineral wool or slag wool or "rock wool" insulation. Microscopic Images of mineral, stone or vitreous fibers are provided.

This mineral wool or "rock wool" insulation article series illustrates and describes mineral wool or "rock wool" and slag wool insulation materials. Rock wool or "rockwool" insulation is also called mineral wool and slag wool though there can be differences among the components of these insulations. We describe old-house or "antique" mineral wool insulation as well as modern mineral wool insulating products still used in buildings.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Mineral Wool Insulation Under the Microscope

Dark brown fibrous insulation needed to be identified (C) Inspectapedia.com JVAOur first photo shows fibrous insulation sent to us by a reader who asked that it be identified.

While we describe variations in the appearance of mineral wool in a companion article - MINERAL WOOL APPEARANCE VARIATIONS - the usual colors of this insulating material range from white to a dirty gray.

We added this reader's photo to that article as well as other photos of his insulation sample to show that his insulation appeared in three color mixes.

In this article we provide forensic laboratory photographs and details that identify this insulation as mineral wool or slag wool.

Particularly where the insulation is many years old we may also find dust contaminants in the insulation that include insect fragments, road dust and debris, and occasionally mold spores and fungal hyphae.

[Click to enlarge any image]

If a building has been re-roofed we might find debris from roofing material such as mineral granules and fragments of asphalt from the roof-work.

The mixed rock-wool fragment below was from the same building as the all-brown-gray sample above.

This is what the reader provided for lab analysis. We found mineral wool and asphalt fragments.

Color variations appeared to be principally due to a mix of mineral wool of different compositions, perhaps different batches of slag or minerals from which the insulation was heated and spun into fibers.

Mineral wool insulation under the stereo microscope (C) Daniel Friedman JVA

Lab photos of the slag wool insulation above are given in this article beginning

at SLAG WOOLS SAMPLE

Beginning below are more examples of slag wool or rock wool insulation of various colors and textures as seen under a high powered light microscope..

Gold Bond Rock Wool Insulation Lab Photographs

Mineral wool or  "rock wool" slag wool or stone wool under the microscope: Gold Bond rock wool (C) Daniel Friedman

Above, low power (300x) then higher power (720x) light microscope images of Gold Bond™ Rock Wool insulation.

Gold bond rock wool insulation under the microscope (C) Daniel Friedman

The smooth surface of these fibers of this insulation are microscopically similar to fiberglass, and like fiberglass, under a forensic microscope these fibers will "disappear" under polarized light.

However other fibers such as flax or cellulose, if present in the insulation sample, will show up under polarized lighting.

Mineral wool or slag wool insulation under the microscope (C) Daniel Friedman

Above and below are two photographs of the same mineral wool sample at 1200x magnification.

Above: notice the characteristic square-ended mineral wool or rock wool fiber in this image. That helps distinguish rock wool insulation from fiberglass insulation.

So does our next photograph:

Mineral wool or slag wool insulation under the microscope using polarized light to see other fibres (C) Daniel Friedman

Above: our second photograph uses polarized light to show included fibers in the same sample that are not in fact mineral wool.

Fibres such as flax, linen, or other organic substances were added to mineral wool or slag wool by some processes in order to improve the insulation's coherence or adherence and to reduce sagging when the insulation was installed in walls.

A closer look at this fiber suggests this may be flax, similar to linen.

Below: additional microscope images of mineral wool insulation showing the broken end of an individual fiber.

In the first photograph just below you can see a fragment protruding from the broken mineral wool insulation fiber end. This is unusual and is similar to the ends of fiberglass fibers that break with a concoidal fracture.

Mineral wool insulation fiber end (C) Daniel Friedman

Below, our second, more gray photo shows rather more typical square-ends of fibers in a sample of mineral wool insulation.

Mineral wool fiber end, usual case (C) Daniel Friedman

Unlike fiberglass, most of the mineral wool fiber ends we examined in this sample had square-cut ends without a concoidal fracture or fragments.

Below: a high power light microscope image of Gold Bond Rock Wool insulation showing the resin binder on crossing fibers.

Gold Bond Rock Wool insulation resin binder and fibers (C) Daniel Friedman

These enlarged slag wool / stone wool photographs were taken at roughly 1200x using Gold Bond Rock Wool insulation mounted in triacetin.

Below my macro-photograph of slag wool insulation shows characteristic globules of blast furnace debris.

Slag wool insulation identified by blast furnace debris (C) Daniel Friedman at InspectApedia.com

Below: glassy globules visible under low power magnification of a mineral wool fiber sample, changing our lighting method from the photo above. [Click to enlarge any image]

Glassy globules in mineral wool insulation (C) Daniel Friedman

Lab Analysis of Reader's White & Dark-Brown to Black Mineral Wool Sample

White and black or dark brown fibrous insulation needed to be identified (C) Inspectapedia.com JVA

Above: a reader mailed this sample of insulation for identification. [Please do NOT attempt to mail us samples for laboratory analysis unless we have previously agreed by email to perform that service.]

[Click to enlarge any image]

We photographed the insulation sample above at various magnifications under the stereo-microscope (below) and under a POLAM high-powered light microscope at magnifications up to 1200x.

This series of photographs confirms that the material is mineral wool, shows mineral wool fibres of several colors including hyaline (colorless that appears "white" to the naked eye), and dark brown that appears gray or almost black to the naked eye.

Particle contaminants in mineral wool insulation (C) Daniel Friedman at InspectApedia.com

Our slag wool photo below, taken from this sample under the stereo microscope and digitally-enlarged, illustrates the presence of spherical particles (red arrows) that are probably an artifact of the slag wool production process that involves the melting and spinning of mineral or slag raw materials.

Spherical particles in mineral wool insulation (C) Daniel Friedman at InspectApedia.com

Our greatly-enlarged view of one of these black particles, shown at 1200x, gives more detail.

Spherical particles in mineral wool insulation (C) Daniel Friedman at InspectApedia.com

We found other black particles in this insulation, possibly asphalt, used as a binder, and still other particulate contaminants that are common in older insulation such as mold hyphae and spores and non-fungal granular debris typical of road dust or soil particles.

We examined this slag wool insulation sample at increasing levels of magnification to study its various components and properties.

Mineral wool at 120x (C) Daniel Friedman at InspectApedia.com

Above: at 120x we see a range of rock wool fibre diameters, lengths, shapes, and colors as well as particulates in the insulation sample.

Below is a portion of this mineral wool sample magnified to 720x, prepared in lacto-phenol as a mounting medium.

Rock wool insulation at 720x (C) Daniel Friedman at InspectApedia.com

In the photo above we see two very different fibers. The fractured end of the colorless fiber is not typical: most mineral wool fibers break off in a relatively straight or square-cut end.

But don't let the presence of an occasional fractured end fool you into thinking this is fiberglass (whose ends terminate in a concoidal fracture). This is not fiberglass.

Most likely the darker square-end fiber is either from a different batch of mineral wool or slag wool produced by the same fabricator but at a different time, later mixed together.

The mineral wool picture above also shows us that there is plenty of non-fungal granular debris in the sample: "dirt" or soil particles possibly from road dust or airborne soil dust.

Hyphal fragment in mineral wool insulation (C) Daniel Friedman at InspectApedia.com ...

Above and just below our photographs illustrate the presence of hyphal fragments and mold spores in this insulation - no surprise in an older building.

Mold spores in mineral wool insulation (C) Daniel Friedman at InspectApedia.com

Below at 1200x in the next two photographs of Rock Wool under the microscope we see the characteristic square-cut end of these mineral wool fiber fragments.

Mineral wool insulation at 1200x (C) Daniel Friedmanb at InspectApedia.com ... Mineral wool insulation at 1200x (C) Daniel Friedmanb at InspectApedia.com

Below we illustrate that mineral wool fibers also vary in shape - not all are simple straight fibers.

Curved mineral wool or slag wool fibers (C) Daniel Friedman at InspectApedia.com

Because in this sample the hyaline fibers were generally straight to slightly curved and the darker fibers were often curved or even branched as in our photo, we inferred that this insulation sample contained mineral wool spun from more than one batch of raw material minerals and slag.

Rock Wool insulation fibers will appear in a sample in a wide range of diameters, from about 1.6 u (micros) to about 80 u in this case.

Our photo below shows a measurement of one of the larger insulation fibers using an eyepiece micrometer with our POLAM microscope at 720x.

Diameter of rock wool insulation fibers (C) Daniel Friedman at InspectApedia.com

At 720x with this microscope each division on the micrometer is about 1.35u.

Counting the divisions on the scale in the photo gives us about 8.5 x 1.35 or about 11 microns as a common size, but we found some fibers much larger in diameter, up to about 80 microns, and other fibers as small as under 2 microns.

 

SEM Photographs & Identification of Fiberglass vs Rock Wool vs Slag Wool

Continuing our discussion of the differences between rock wool and slag wool found

at MINERAL WOOL - ROCK WOOL INSULATION - topic home,

these Scanning Electron Microscope (SEM) photographs have been contributed by Aleksandra Pawelek, an SEM microscopist and project leader in Environmental Laboratory in Poland which provides asbestos and mineral wool analysis of building and road materials. (October 2020) - Email: AleksandraPawelek@eurofins.com

Rock Wool Fibre Identification by SEM

Rockwool morphology by SEM Scanning Electron Microscope (C) InspectAPedia.com Alexsandra Poland

[Click to enlarge any image]

You will notice that in these Scanning Electron Microscope analyses of Stone Wool (Rock Wool) insulation the system automatically detected these elements:

Mg, Ca, Ti, Cr, Mn, Fe, Al, Si, and O and manually identified P, Na, K. For those readers not familiar with the atomic symbols found in the periodic table we can also write these as

Sodium, Magnesium, Potassium, Calcium, Titanium, Chromium, Manganese, Iron, Aluminum, Silicone, Oxygen , Phosphorous.

Here is the chemical composition of reference rock wool fibre in reference to German standard VDI 3492, considers for following oxides:

Rock Wool fibre constituents German standard VDI 3492, courtesy Environmental Laboratory, Poland - at InspectApedia.com

[Click to enlarge any image]

Below: Rock wool insulation SEM photograph by our contributor with marked typical dimension.

Rock wool insulation SEM photograph (C) Eurofins & InspectApedia.com

Glass Wool Fibre Identification by SEM

Rockwool morphology by SEM Scanning Electron Microscope (C) InspectAPedia.com Alexsandra Poland

You will notice that in these Scanning Electron Microscope analyses of Glass wool insulation the system automatically detected these elements:

Na, Mg, K, Si, and O and manually identified Ti, Cr, Mn, Fe, Al, P. For those readers not familiar with the atomic symbols found in the periodic table we can also write these as

Sodium, Magnesium, Potassium, Calcium, Titanium, Chromium, Manganese, Iron, Aluminum, Silicone, and Oxygen , Phosphorous.

Below is the chemical composition of reference glass wool fibre in reference to German standard VDI 3492, considers for following oxides:

Glass wool fibre identification reference German Standard VDI 3492 courtesy of Environmental Lab Poland at InspectApedia.com

Below: Glass wool insulation SEM photograph by our contributor with marked typical dimension.

Glass wool insulation fibres under the SEM (C) Eurofins & InspectApedia.com

Slag Wool SEM Identification Photographs & Composition Data - samples wanted

Slag Wool SEM Identification Photographs & Composition Data

Additional analysis of slag wool insulation will be posted here when available.

Glass wool insulation fibres under the SEM (C) Eurofins & InspectApedia.com ... Glass wool insulation fibres under the SEM (C) Eurofins & InspectApedia.com

Any reader who can provide a sample which could be classified as slag wool

Glass wool insulation fibres under the SEM (C) Eurofins & InspectApedia.com

Please contact : AleksandraPawelek@eurofins.com

and/or contact InspectApedia.com using the page top or bottom CONTACT link.

 

Mineral Wool or Rock Wool Research & References

APC Standard VDI 3492 cited at InspectApedia.com

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