Wallboard: It’s more than joint compound
Andrew F. Oberta, MPH, CIH
The Environmental Consultancy

Over the past few years I have probably taken more bulk samples of wallboard than any other material. One reason is that the law in Texas requires an asbestos survey to get a building permit and many renovations involve the removal of walls. I have come to realize how complex wallboard systems, to use the proper term, can be, and which components are most likely to contain asbestos.

Whether you call it wallboard, drywall or the trade name Sheetrock, the basic building material is a gypsum core with paper facing. I have never found asbestos in these materials. The stuff that is applied to it makes it a wallboard system, and these are the materials that have asbestos in them. Figure 1 shows a few of the combinations that make up wallboard systems, not all of which are vertical. Horizontal wallboard systems that use these materials are called ceilings.

Figure 1. Wallboard finishes

Figure 2. Wallboard joint compound and skim coat

When wallboard is installed the seams (joints) between the sheets are often – but not always – filled with a paste commonly called “joint compound.” This paste was previously made with chrysotile asbestos fiber and it is still legal to do so. After the paste is troweled smooth a strip of cloth or paper tape is laid over it – this tape can also have asbestos fiber in it. More joint compound is smeared on and smoothed out in what is called a “tape and float” operation. Carefully done, it results in a seam that is virtually invisible.

Bear in mind that wallboard is installed with horizontal as well as vertical seams. Also realize, as Figure 2 shows, that the installer may have smeared the joint compound some distance – as much as a foot – on either side of the joint. He also used it to cover nail holes and surface imperfections that are nowhere near the seams. Hence, ASTM E2356 Standard Practice for Comprehensive Building Asbestos Surveys also uses the term skim coat, defined as “a thin finish coat applied to an existing plaster surface or other substrate to improve appearance or other reasons.”

ASTM E2356 describes sampling methods for wallboard and other common asbestos-containing materials. The ASTM Manual on Asbestos Control: Surveys, Assessment, Abatement and Maintenance– Third Edition, of which I am the author, discusses this and other asbestos control standards.

Figure 3. Joint compound sample

Figure 3 shows a sample of joint compound where the material in the gap between the sheets is clearly visible. Figure 4 is another sample showing the joint compound in the gap between the sheets. Does this mean we need only look for joints to properly inspect a wallboard system? Not at all – look again at Figure 1.

Samples I have taken from walls and ceilings in locations well away from the seams have contained a thin layer of asbestos material that is better described as a skim coat than joint compound. This material is sometimes found in combination with a thin layer of plaster that was applied to the wallboard, but only the skim coat and not the plaster contains asbestos. Some refer to this as a texturizer and the purpose seems to be to provide a smooth surface for painting. Figure 5 shows two examples of multiple layers in wallboard systems, including the asbestos-containing skim coat or texturizer.

Figure 4. Wallboard sample with joint compound

Figure 5. Asbestos-containing skim coat in multi-layer systems

Figure 6. Asbestos-containing textured paint

Figure 7. Textured "popcorn" ceiling finish

Another component of the wallboard system that can contain asbestos is the paint. The heavier the texture the more likely that asbestos fiber was added as a filler: Figure 6 shows asbestos-containing paint on a wall where a sample was taken. This is not to be confused with the ceiling finish sometimes called a “popcorn” ceiling, where the texture is provided by tiny polystyrene beads in addition to asbestos fibers. Figure 7 shows such a ceiling in an apartment that contained 5% chrysotile asbestos. Whether it’s a “popcorn” finish or plaster may not be known until the sample is analyzed; the important lesson is that textured walls and ceilings need to be sampled.

Sampling Wallboard Systems

Since joint compound is a suspect asbestos-containing material, one tries to find the joints or seams, which usually occur on the vertical studs or horizontal braces. These studs or braces can be located with an electronic stud finder (Figure 8). However, not every stud or brace has a seam and more than one location may have to be tried in order to find a joint. In some cases the wallboard is unfinished (Figure 9) or the joint is obvious because it isn’t smoothly finished (Figure 10).

Taking a sample of a wallboard system means defacing the wall, which is generally frowned on unless the wall is coming out during a renovation or demolition. For a Baseline Survey as described in ASTM E2356, one therefore looks for locations where wallboard can be sampled without aesthetic damage. If damage to the wall must be avoided there are other ways to find and sample a joint.

Figure 8. Electronic stud finder

Figure 9. Unfinished wallboard

Figure 10. Visible vertical wallboard joint

Figure 11. Wallboard joint behind cove base

Pull back the cove base far enough and you will find a wallboard joint (Figure 11). If there is joint compound there, sample it and replace the cove base, or sample the wall directly above. Look above a lay-in ceiling: the finished wallboard and joint will extend part-way into the plenum (Figure 12). It may be necessary to peel back wallpaper to find the joint (Figure 13). As Figure 5 illustrates, however, it isn’t necessary to sample a joint in order to find asbestos in a wallboard system.

Figure 12. Joint and compound in ceiling plenum

Figure 13. Wallpaper covering horizontal joint

Figure 14. Wallboard sampling using knife

Appendix X1 to ASTM E2356 describes a method for sampling wallboard systems that stresses the need to sample all layers of material in the system. This requires removing a substantial amount of the material, using a coring tool such as a hole saw, a sharp knife (Figure 14) or my weapon of choice, an industrial hole punch (Figure 15). I use this device to gouge out a strip about three inches long and deep enough to penetrate into the gypsum core. It is the best method I have found for wallboard sampling.

Each layer of the sample must be analyzed separately and the asbestos content (or lack thereof) reported for each layer . Be aware that some laboratories charge by the sample and others for each individual layer. The lab may also report a “composite” result for all layers, which invariably will be less than one percent asbestos. Let’s discuss composite sampling issues.

Figure 15. Wallboard sampling using hole punch

Composite Sampling and Analysis

It goes without saying that one never physically combines separate layers of any sample for analysis. Composite sampling and analysis actually refers to arithmetically combining the results of analyzing separate layers into a single number. Opinions and regulations on doing this differ widely. The only ones in favor of it seem to be EPA – with some restrictions – and those who would like to avoid an asbestos abatement project when removing wallboard.

EPA issued a “clarification” to the NESHAP on January 5, 1994 regarding wallboard systems and clarified their clarification on December 19, 1995. I will not attempt to explain these “clarifications,” but those who indulge in regulatory nuances are welcome to follow the links to the actual text. The bottom line is that EPA lets you treat a wallboard system with a composite asbestos content of less than or equal to one percent as non-ACM – providing you can figure out which components can be composited and which cannot.

Others disagree. OSHA does not allow compositing of sample results, nor does Texas to name one state. ASTM E2356 does not allow it. The reason is clear: if a layer of the wallboard system contains asbestos in any amount, disturbing it can create an exposure hazard with airborne fiber levels that can even exceed the OSHA Permissible Exposure Limits.

Wallboard system sampling results

Asbestos is found in wallboard materials more often than you might think. I have sampled these materials in over a hundred buildings and compiled the results from 2009 to 2012. Here is a summary -- "positive" samples contained >1% asbestos.

Samples of
Number of samples
Positive samples
Percent positive
Walls and Ceilings

These samples were taken from the materials described on this web page: joint compound, plaster, paint, texturizing finishes and “popcorn” ceilings – anything that is part of the wallboard system. Asbestos content was mostly reported as 2% chrysotile but a few samples were as high as 5%. The buildings from which these samples came range from those constructed fairly recently to some that are several decades old. The older the building, of course, the more likely asbestos will be present and these percentages do not represent the probability of finding asbestos-containing wallboard materials in any specific building. But the point is made: a significant percent of wallboard systems contain asbestos.

Friable or non-friable?

The answer is both. A piece of joint compound may be so hard that it is difficult, if not impossible, to crush to powder by hand pressure, whereas a layer of skim coat may easily produce airborne dust. ASTM E2356 includes wallboard systems in the friable materials section of Appendix X1 for sampling methods. Removal will render even the joint compound friable, no matter how hard it has set, so the entire system should be treated as friable for purposes of the survey and abatement.

Wallboard systems abatement

OSHA Class I or Class II? That depends on whether or not the material being removed is considered a surfacing material by OSHA, and an interpretation they posted on 05/14/1998 is titled: “Asbestos standard: Joint compound is not a surfacing material.” It concludes that removal of wallboard is Class II work, and other interpretations they posted agree.
However... that interpretation assumes that only the joint compound contains asbestos. As we have seen, other components that are clearly surfacing material, such as textured finishes, are part of wallboard systems. I have an e-mail from an EPA Regional Asbestos Coordinator stating that the agency considers paint to be surfacing material; OSHA says it depends on the thickness.

Regardless of whether you consider it Class I or Class II work, and regardless of the asbestos content of the various components, it comes down to doing the work under full abatement precautions and with the same thorough work practices you would use for any asbestos-containing material. Some examples of removing wall and ceiling systems are shown in Figures 16 and 17.

Figure 16. Removing wallboard system

Figure 17. Removing ceiling system
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