Chinese Drywall FAQs

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Frequently Asked Questions (FAQs)

Q: Is elemental sulfur (S8) the cause of corrosion in homes? What is the mechanism?
Q: What is the characteristic odor of corrosive Chinese drywall?
Q: Which reduced sulfur compounds are emitted from corrosive Chinese drywall?
Q: Can I simply measure the concentration of reduced sulfur gases in the indoor air to diagnose whether I have a problem?
Q: Doesn’t all drywall contain sulfur?

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Q: Is elemental sulfur (S8) the cause of corrosion in homes? What is the mechanism?

A: Elemental sulfur (S8) is a marker compound of corrosive drywall — meaning that it is found only in corrosive drywall and it is not found in non-corrosive drywall. Its presence is not necessarily causative. The mechanism of the reaction that causes corrosion in homes is not fully understood by experts at this time. ALS Environmental makes no claim as to the cause of the reaction — we simply test for presence/absence of the marker compound (S8).

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Q: What is the characteristic odor of corrosive Chinese drywall?

A: The most common description of the odor associated with corrosive Chinese drywall is a “burnt match” sulfurous odor.

Many of the odor-causing compounds associated with corrosive drywall can be detected by the human olfactory system at very low concentrations. For example, the odor recognition threshold for hydrogen sulfide is generally accepted to be between 0.50-2.0 ppbV.

The characteristic “burnt match” odor associated with corrosive drywall is likely an amalgamation of many different odorous compounds, not merely the most commonly mentioned compounds hydrogen sulfide, carbonyl sulfide, and carbon disulfide.

Research presented by ALS Environmental at the Technical Symposium on Corrosive Imported Drywall in November 2009 revealed at least 18 odorous chemical species identified by gas chromatography/mass spectrometry (GC/MS) which are emitted from corrosive drywall. Click here for a summary of this info: http://www.caslab.com/News/identify-problem-chinese-drywall.html

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Q: Which reduced sulfur compounds are emitted from corrosive Chinese drywall?

A: The primary reduced sulfur compounds that are emitted from corrosive Chinese drywall are hydrogen sulfide (H2S), carbonyl sulfide (COS), and carbon disulfide (CS2). It should be noted that COS and CS2 can also be emitted from non-corrosive drywall, but based on our research, the emission of H2S seems to be exclusive to corrosive drywall.

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Q: Can I simply measure the concentration of reduced sulfur gases in the indoor air to diagnose whether I have a problem?

A: The concentrations of reduced sulfur compounds seen in indoor air impacted by corrosive drywall are extremely low, typically in the part-per-trillion (pptV) to low part-per-billion (ppbV) range.

The limit of detection for even the most sensitive analytical instrumentation currently available (gas chromatography/sulfur chemiluminescence detection: GC/SCD or gas chromatography/mass spectrometry: GC/MS) is only slightly higher than this range at about 2.5 – 5.0 ppbV.

Because the concentrations at which the odorous compounds can be present are so close to the analytical detection limit,  it is ALS Environmental’s opinion that indoor air sampling with Tedlar bags or canisters for reduced sulfur gases is in most cases ineffective.

Passive diffusion monitors such as the Radiello® RAD-170 device may be used to monitor very low indoor air concentrations of hydrogen sulfide over a long period of time (1-2 weeks). These monitors collect hydrogen sulfide via a reaction with zinc acetate-coated sampling media, which forms a stable zinc sulfide. However, the RAD-170 monitor can only be used for hydrogen sulfide and not for other reduced sulfur compounds. An emission test performed on bulk drywall can be an effective means to measure all reduced sulfur gas emissions.

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Q: Doesn’t all drywall contain sulfur?

A: Yes, it does, but sulfur can be present in different chemical forms or states, which makes a difference.

Drywall is comprised of gypsum (calcium sulfate dihydrate), for which the molecular formula is CaSO4 ∙ 2 H2O. Therefore, the sulfur in gypsum is primarily in the sulfate (SO4 form).

Elemental sulfur, a solid, can exist in various states, including the orthorhombic cyclooctasulfur allotrope, commonly referred to as “S8”. It is this unique allotrope of sulfur that has been identified as a marker compound of corrosive drywall, not the sulfate form of sulfur. 

When testing suspect drywall to determine if it is corrosive, it is important to make the distinction between a “total sulfur” test, which should always produce a positive result for sulfur, and a test for the S8 elemental sulfur allotrope.

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