Concrete is evaluated for moisture content using a calcium chloride test. Calcium Chloride, a highly hygroscopic salt, is exposed to the new concrete under a small plastic dome that is sealed to the floor. The amount of water it absorbs in a specific time is measured to determine how dry the concrete has become. The readings are expressed in lbs/1000 sq. ft./ 24 hrs. This is a measure of vapor transmission.

"Our floor was measuring over 8.6 lbs," said Schueller. "We needed to lower the moisture content to less than 5 lbs before flooring could be adhered."

Fortunately, when Schueller started researching a solution, an associate, Mike Price, S. D. Deacon's operations manager had used Munters, a company that specializes in drying at construction sites.

"We have been providing construction drying services for over 30 years," said David Carlson, an industrial account manager with Munters Moisture Control Services, who works out of its Portland office. "But mostly in Europe where integrating drying with construction activities is common place. In the United States, construction drying is 'new' idea that is coming into fashion with increased pressure to finish projects on time or ahead of schedule."

Munters uses industrial desiccant dehumidifiers, which have been especially modified to move on and off construction sites, to do the drying. The high volume dehumidifiers produce extremely dry air that is circulated inside a construction environment. The dry air pulls moisture molecules out of substances like concrete, masonry block, joint compound and paint allowing them to dry in record times.

"Munters dehumidifiers are used to protect the Space Shuttle before launch," said Carlson. "More than 10,000 manufacturing sites control their process environments with a Munters dehumidifier. We use them to dry out buildings after floods. They keep mothballed battleships from rusting. Desiccant dehumidification is an amazing technology that is used throughout American industry."

At Best Buy, Munters installed three of its high volume construction site dehumidifiers outside the building and strategically distributed dry air throughout the interior, using a network of flexible ducting.

"I'd never heard of drying concrete," said Joe Schueller, "but I told Munters if they could do what they said, they'd better get right to it because my deadline had our backs to the wall." "I don't think Joe thought desiccant drying would work," said Carlson. "Dry air is invisible and many of our customers at first have a healthy skepticism ... but the proof is in the results."

In three weeks, Munters had dried down the concrete slab to 4.4 lbs/1000 sq. ft./per 24 hours and was gone from the site. Not only had the floor reached a safe moisture content for tile and carpet to be adhered, but several unexpected advantages emerged as bi-products of the drying process.

"The building needed the masonry block walls sealed and painted"" said Carlson. "The wall had soaked up water during rainstorms which occurred before the roof was completed. Discoloration indicated moisture in the block walls. With February weather outside and high humidity from the floor inside, there was no way that wall could dry on its own. But as we dried the floor, the wall also dried."

Joe Schueller was impressed with the effect that drying had on the drywall schedule. "I've never seen drywall go faster," said Joe. "We had five men taping and applying mud to the joints on a 225 foot long sheetrock wall. By the time they worked the length of the wall-about five hours--they could start again on the other end. The progress was incredible; drying cut days out of the drywalling effort."

"One thing you can't do in the construction business is miss the deadline," said Schueller. "We didn't at Best Buy thanks to Munters. If I were in a similar situation, you can bet I'd call Munters back again."

Publication date: 02/19/2001