June 30, 2010
Getting Techie On Chinese Drywall
By Michael D. Shaw
While current news coverage on the subject of Chinese drywall might be concentrating on the various pending lawsuits, affected homeowners should be glad to know that one federal agency is working on the case—overtime. That would be the Consumer Product Safety Commission (CPSC).
CPSC has produced a number of useful documents on Chinese drywall, all available on its Drywall Information Center website. Topics of recently completed reports include
The drywall emissions chamber work was performed—at no small cost—by the famed Lawrence Berkeley National Laboratory, and examined 30 samples of drywall. Both Chinese and domestic product were investigated in the study, and were subjected to extensive testing, that included measurement of reduced sulfur compound emissions, and strontium content.
Although technically brilliant, the report was criticized by some because two particularly glaring findings were presented without comment. Indeed, I was one of the critics. Here are those findings:
Three samples were tested from Knauf Plasterboard (Tianjin) Company, Ltd., a name quite familiar to those following the Chinese drywall saga. The samples were identified by year of manufacture, namely 2005, 2006, and 2009.
In terms of the all-important hydrogen sulfide emissions, the 2005 sample was the worst of all the 30 samples, exuding hydrogen sulfide at a rate of 203.27 micrograms per square meter per hour. But, a sample from the same factory dated 2006 emitted 40 percent less at 118.83. And, the 2009 sample was only slightly worse than some domestic product at 4.99 micrograms per square meter per hour.
Assuming that the samples were representative of typical production, the obvious question is: What changed during those years at the factory?
Moreover, there were three samples—all from 2006— from Taian Taishan Plasterboard Company, Ltd. In terms of hydrogen sulfide emissions, they came in at 185.14, 67.11, and 24.75. Again, one must ask: What changed in the manufacturing process?
I was to find out later that these questions were raised by CPSC, but went unanswered, and diplomacy prevented the agency from commenting further. As to my criticisms, I partially withdraw them, in that the agency should have at least noted the issues and referred to "ongoing discussions" with the factories.
The CPSC's latest report takes a look at so-called "source markers." A source marker would be a quick and accurate method of identifying problem drywall without having to resort to elaborate chamber testing, and could even supplant the visual inspection procedures currently in use. Visual inspection focuses on the effects of tainted drywall such as sulfide-induced corrosion of wiring and HVAC coils.
Early on, it appeared that the strontium content of drywall would be a good marker. As luck would have it, x-ray fluorescence (XRF) spectroscopy is an elegant technique for determining the strontium content of drywall. Manufacturers of these instruments were touting XRF units as the one tool that had to be in every drywall inspector's tote bag. High levels of strontium (greater than 1200 mg/kg) should correlate with problem drywall, no fuss, no muss. Non-destructive testing at its easiest and best.
XRF was also suggested for warehouse testing of drywall, before it would be used in construction.
But then, the results from Lawrence Berkeley appeared.
To say that they are disappointing for XRF advocates is a gross understatement. Remember that Taian Taishan sample that put out 185.14 of hydrogen sulfide, and was rated as the second worst tested? Its strontium content was a mere 273 mg/kg. Then there's a super-clean American board with no measurable hydrogen sulfide, with strontium at an eye-popping 2580 mg/kg.
How about one of the lowest emitting Chinese samples tested, with virtually unmeasurable sulfide emissions, and an astounding 5890 mg/kg of strontium?
Of course, even if strontium were definitive for problem drywall, there were always practical issues with using an XRF "gun." Note that the Lawrence Berkeley testing was done on unfinished board. In homes, drywall is usually finished in some manner, either with paint or a wall covering. Who knows how much strontium could be introduced into the mix by the enormous variety of paints and wall treatments, thus affecting the readings.
Another glitch is that homes can show the effects of problem drywall if only a very small percentage of the boards are tainted. How does an inspector scan every single piece of drywall in a house, without asking the homeowner to move all his furniture?
That's why visual inspection is currently the state of the art. Skilled practitioners claim near 100 percent accuracy in finding affected homes, based on subsequent lab testing of drywall from the homes.