Construction of a large luxury resort located in a warm, humid climate was coming to a close during the summer. Because the vinyl wall covering on the interior side of the exterior walls had an impermeable finish, it functioned as a vapor retarder (also referred to as a vapor barrier).

The HVAC system consisted of a continuous toilet exhaust and packaged terminal air-conditioner (PTAC) units. The outside air exchange rate in each guest room averaged six times an hour, all from infiltration.

In this case, problems developed both inside the building and inside the wall.

The combined effect of excessive outside air infiltration and an improperly located vapor retarder caused $5.5 million in moisture and mold damage, even before the facility was opened (Figure 1). If these same design combinations had occurred in a more temperate climate, the problems would have been limited to increased energy consumption and possible complaints about guest comfort.

This is one example of how hot, humid climates present unique challenges that are often overlooked by the design and construction community. However, challenges also occur for buildings located in other climates. Meeting these challenges depends on understanding a building’s local climate conditions and how they contribute to IAQ and mold problems.

 

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There’s an assumption in the hotel industry that plaster walls are not susceptible to mold growth–but don’t let your guard down. Experts at Liberty Building Forensics Group (LBFG) helped guide a hotel renovation team that encountered an unsuspecting mold problem in the hotel’s plaster walls that could have cost millions of dollars in remediation and lost room revenue.

 

Mold growth is not seen as frequently on plaster walls as it is on gypsum wallboard, primarily because there are no nutrients to support mold growth (except for any dirt or dust that might be on the plaster). As a result, any mold growth on plaster walls is often not very visible or extensive, so most hotel owners and operators in this situation feel relatively safe from mold problems. It is important to realize, however, that what unexpectedly happened to this high-end hotel with plaster walls in the heart of Washington, D.C. could happen to anyone.

 

CASE SUMMARY

Hotel management was attempting to fast-track a renovation project because of a high demand for room nights in this particular location of Washington, D.C. Part of the renovation process involved removing all the old vinyl wall covering on the corridor walls and in the rooms themselves, then patching and repairing the underlying plaster with skim coats, allowing that to dry before installing the new vinyl wall covering.

 

Much to the dismay of everyone involved, mold was found growing behind the new vinyl wall covering while renovations were still ongoing. The mold was found growing primarily on the adhesive (which served as a nutrient), as well as on any dirt and dust that might have been on the plastered surface. This mold growth caused a discoloration of the vinyl wall covering, with pink stains appearing on both the room and corridor sides of the vinyl. The discoloration was noticeable to the hotel staff and would have been noticeable to guests as well, thus bringing this fast-track renovation to a halt.

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