In the United States, the 1970’s saw the extensive use of drywall (gypsum board with paper on both sides) in both residential and commercial construction. This was mainly because drywall construction costs 50% less than plaster construction. Thus began the introduction of “mold friendly” building materials into homes, commercial, and industrial buildings. The paper and glues in drywall are organic materials that can support mold growth when they become wet. Plaster, on the other hand, contains very little organic matter to retain water or to support mold growth (Occasionally, horsehair and cellulose can be found in the rough coat.) Plaster also has a final coat of ‘lime plaster’ which is mostly calcium hydroxide. Lime plaster is very alkaline when wet, which further inhibits microbial growth. Therefore, drywall is much more “mold friendly” than plaster.

The next factor in the start of the mold problem was energy market manipulation in the mid 1970’s. The oligopolistic major oil companies induced a fabricated “oil shortage” by holding imported oil in tankers off shore and creating a so-called “energy crisis.” This contrived oil shortage was similar to the one created in the early 1920’s (see newspapers of that time for references). The prior contrived shortage also resulted in significantly increasing oil prices and corporate profits. This also ushered in an era of “energy conservation” in the US.

Note: Another example of “repeating history when we failed to learn from it” occurred in the area of ventilation standards. In December 1981, in response to the contrived “energy crisis” mentioned above, the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) reduced the required amount of outside make-up air from 15 cfm per person to only 5 cfm per person. This ventilation standard (ASHRAE 62-1981) clearly disregarded earlier research that showed a health risk from low ventilation rates. Shortly thereafter, the indoor air quality /sick building problems of the 1980’s began to surface. In January of 1983, ASHRAE rescinded its 62-1981 standard due to “health concerns.”

Worse yet, thousands of buildings continued to be built a number of years after that using the unhealthful ASHRAE 62-1981 for. The main reason for this continued unhealthy construction was the common practice in the US of using the “low bidder.” Mechanical engineering firms would win contracts by being the low bidder using the ventilation system requirements of ASHRAE 62-1981 (5 cfm/person) over the higher bids of competing companies using the correct, older ventilation requirements of ASHRAE 62-1976 (15 cfm/person).

Professional mechanical engineers, even though they were aware of the “health concerns” statement by ASHRAE, were under no “legal” duty to inform prospective building owner of the unhealthiness of 62-1981, since this is only a guideline. As the same time, few building owners were unaware that ASHRAE had retracted the newer standard. Consequently, the practice of building poorly-ventilated buildings continued throughout the 1980’s until the formal reissuing of this standard by ASHRAE in 1989. Many local government code bodies, also unaware that ASHRAE had rescinded the 62-1981 standard, continued to specify these unhealthful ventilation rates until 1990.

Consequently, many homes and commercial buildings built during that decade were “tightened up” to reduce heating and cooling costs. Insulation standards increased and infiltration rates were decreased. The consequence of this was that when drywall became wet, due to decreased wall air infiltration and less ventilation of moisture-ladened air, it did not dry out as quickly as it did in the past. Mold growth became a problem after even relatively minor water intrusion events.

In the 1980’s, Canada and the Scandinavian countries, as an extension of the concern about radon gas in homes, began to study indoor mold levels. The computerized national healthcare record systems in these countries made identifying mold related health symptoms an easy task. This disease incidence data could then be compared to specific mold levels in individual patient homes. These countries subsequently developed “acceptable” mold standards for housing. These standards are still in use today.

Two of the major studies of the relationship of indoor mold to occupant illness in homes were conducted in the Netherlands 352 and Taiwan 336 in the early 1990’s. Neither of these studies found a directly relationship between reported symptoms and mold spore levels. However, the reporting of “damp” conditions in the home clearly was related to an increased risk of respiratory disease.

In the 1990’s, the potential health implications of indoor mold growth were finally broadly recognized in the United States. Further, buildings containing “mold-friendly” building materials were now widespread throughout the United States. Interestingly, Germany, Poland, Columbia, the Czech Republic, Slovakia and many other countries still require the use of plaster instead of drywall and coincidently do not have as many mold problems as are found in the United States.

Note: An interesting story regarding to the use of plaster occurred in 2000 when the Czech Republic experienced extensive flooding. The AIHA contacted officials in that country and offered them help with mold problems resulting from the flooding. The officials wrote back to the AIHA and said they had very little mold problems from the flooding because they don’t use drywall.

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