Case Study No. 2: Hospital
Similar adhesive problems were identified in a new hospital facility in the Pacific Northwest constructed in 2003 and 2004. The majority of the floors in the facility consist of normal weight concrete slab-on-grade. Unlike the office building example, the new slabs were placed over a vapor retarder and a 2 in. thick compacted sand blotter layer. Floor finishes include VCT, various types of sheet vinyl, and carpet tile in the different areas of the hospital.
The maximum concrete moisture vapor emission rates (MVER) allowed by the various manufacturers of the floor finishes and adhesives was 3 lb measured in accordance with ASTM F1869. Tests performed on the new concrete before flooring was installed showed that actual moisture levels ranged from 4.8 to 7.6 lb. The pH levels on the concrete surface were low, ranging from 7 to 8. To address the elevated levels of moisture, the contractor installed a moisture mitigation coating on the surface of the slab prior to installation of the flooring. The product literature for the mitigation coating stated that it would reduce MVERs from up to 12 lb down to 3 lb. Following installation of the moisture mitigation coating, the finish flooring was installed during the last several months of construction.
A little over a year after construction was complete and the hospital became operational, problems with the floor were reported. The visual evidence of flooring issues with the sheet vinyl flooring includes ripples, bubbles, and liquids seeping from seams. Carpet tiles were easily removed from the floor, revealing wet and uncured adhesive. The VCT flooring exhibited cracking and lifting, especially aligning with joints in the concrete substrate. Additional moisture testing was performed following reports of issues with the flooring. At that time, reported MVERs ranged from 5.2 to 7.1 lb directly on the surface of the concrete. Tests conducted on the surface of the moisture mitigation coating ranged from 4.3 to 4.5 lb. The pH readings ranged from 7 to 10 directly on the surface of the concrete, and 6 to 7 on the surface of the moisture mitigation coating.
In an attempt to mitigate the problems, the contractor replaced the flooring in several areas of the hospital, such as installing new sheet vinyl in the operating rooms. The replacement protocol included removal of all existing floor materials, and shot blasting and grinding of the concrete slabs to achieve a rough concrete surface profile without any residue from the previous materials. A second moisture mitigation coating was then applied to the surface of the concrete slab, followed by the installation of a cementitious leveling underlay – ment and new sheet vinyl flooring. Shortly after installation of the replacement floor system, liquid-filled blisters appeared in the new flooring over the second moisture mitigation coating.
Moisture testing was performed subsequent to the formation of blisters in the replacement sheet vinyl. These MVER readings ranged from 11.6 to 5.8 lb. Internal concrete RH readings were collected in accordance with ASTM F2170
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using a modified Protimeter MMS+ system. These readings ranged from 85 to 97 %. The pH readings on the surface of the concrete ranged from 9 to 11. Samples of the compacted sand blotter layer between the concrete slab and vapor retarder were collected and were measured for moisture content. The typical moisture content of the sand blotter layer was about 3 to 6 % by weight.
Additional testing to further understand the existing conditions was performed. Chemical analyses on the various adhesives, moisture mitigation coatings, and liquid from blisters were conducted. The results of these analyses showed that the first moisture mitigation coating was an emulsion-based product composed of agglomerates of acrylic, making it water-soluble and insufficiently dense to prevent or reduce moisture diffusion. The second moisture mitigation coating was also found to be an emulsion-based product (polyvinyl acetate) with a large amount of filler particles of titanium. These properties resulted in a mitigation coating that re-emulsified in the presence of water and allowed some vapor diffusion. Moisture vapor from the concrete and sand blotter layer migrated through the moisture mitigation coatings and degraded the adhesive. Adhesive degradation occurred with or without a moisture mitigation coating, and under four different types of flooring. Similar to the office building, we recommended complete removal of all existing floor materials, installation of an effective moisture mitigation coating, leveling underlayment, and finish flooring with their respective adhesives.