Case Studies No. 1: Office Building

In 2006, the general rehabilitation of a 1970s office building included installa­tion of new carpet and VCT on an existing concrete slab-on-grade. A few years after the rehabilitation work, the new carpet and VCT developed blisters, debonded, and the flooring adhesive turned soft and gummy intermittently throughout the building. The original slab-on-grade construction did not include a vapor retarder to prevent ground water-based vapor migration through the slab-on-grade. The original flooring system appeared to be VCT or VAT applied with older asphalt-based adhesives. Current conditions show as many as three layers of leveling compound and flooring adhesive have been

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installed over the original asphalt flooring adhesives, which remain on the sur­face of the concrete slab. The newest flooring adhesive layer is the layer that is soft and gummy. Each time the floor was replaced, the loose debonded sections of the old floor adhesives and leveling layers were removed and another layer of leveling compound was applied. The condition of the older layers range from well bonded to having no bond, but none were soft and gummy like the most recent flooring application.

The moisture levels in the slab were measured according to ASTM F1869— Standard Test Method for Measuring Moisture Vapor Emission Rate of Con­crete Subfloor Using Anhydrous Calcium Chloride [7], and the moisture vapor emission rate (MVER) ranged from 3.75 to 10.20 lb/1000 sq ft/24 h (lb). The floor adhesive manufacturer set a MVER limit of 5 lb, and the leveling underlay – ment installer set an MVER limit of 3 lb. The internal relative humidity (RH) levels, measured in accordance with ASTM F2170—Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes using Protimeter MMS+ equipment [8], ranged from 58 to 93 %, although most of the results ranged from the mid-50s to the mid-60s. Although the flooring manufacturer did not specify internal concrete RH limits for their products in 2006, typical industry limits are 75 to 80 % RH.

Most current flooring industry standards and practice guides require removing the old layers of flooring material so the concrete bonding surface will be “permanently dry, clean, smooth and structurally sound." Industry standards such as the Carpet and Rug Institute (CRI-104-2002) and the Resilient Floor Covering Institute (RFCI 1P#2) do not allow installation over older adhesives [9,10]. Although some manufacturers will allow new flooring installation over some existing flooring materials, new flooring adhesives should not be installed over asphalt adhesive because the new adhesive materials will likely not bond to the asphalt residue. Although the asphalt adhesive may provide some vapor – retarding properties, the older asphalt adhesive was discontinuous and ineffec­tive serving as a moisture vapor migration layer. The practice of going over the older adhesive layers is a carryover from many older jobs when the new and old adhesives were of similar composition and compatible; hence, the observed dis­continuous areas of original asphalt flooring adhesive and varying layers of older adhesive and underlayment. Consequently, what may have had limited successfulness many years ago is not working today.

However, the newer latex flooring adhesives turned soft and gummy while the residue of the older adhesives did not show the same level of moisture breakdown when exposed to the same level of moisture. Observation of the ad­hesive failure a few years after installation and only intermittently throughout the building indicates that the adhesive initially cured and provided acceptable adhesion, but later became soft and gummy after prolonged exposure to mois­ture. The rate of debonding and blisters increased with time. Sub-slab soil – based moisture diffused through the concrete slab, collected below the flooring, and caused the deterioration of the new adhesive and flooring system. No evi­dence that an initial cure of the adhesive was affected by the moisture was observed. Removal and replacement of the entire flooring system to the con­crete base layer was recommended. Since the multiple layers of old adhesive

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and underpayment did not provide a suitable substrate for the new flooring sys­tem, they should be completely removed before a moisture mitigation coating and the new floor system are applied.