Moisture Test Exceeds Adhesive Limit with Long-Lead Alternative
A 12,000 sq ft public library reading-room project has a slab-on-grade. Moisture testing by ASTM F2170 reports 88% relative humidity at 40% depth. The specified resilient flooring adhesive, Product A, is limited by its manufacturer to 80% RH. Product B is a different adhesive that the manufacturer permits up to 90% RH, but its lead time is 14 weeks versus 4 weeks for Product A. The project has 6 weeks of schedule float before flooring installation, and the owner wants to open in 19 weeks. The contractor proposes switching to Product B, citing the test result and the float. Product A's data sheet also lists a 10% reduction in bond strength above 80% RH but no prohibition. The design team must respond within 5 business days to keep the flooring subcontractor's order on track. The owner's representative asks whether a moisture mitigation system is a better solution.
1. Compare Product A, Product B, and moisture mitigation as options.
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Product A is not compliant as submitted: 88% RH exceeds its 80% limit by 8 percentage points, and the 10% bond-strength reduction does not cure a manufacturer prohibition. Product B is technically within its 90% limit, but its 14-week lead time exceeds the 6-week float by about 8 weeks and would push the opening past 19 weeks. A moisture mitigation system is a third option: it can reduce the slab RH to Product A's limit and preserve the 4-week adhesive lead time, but it adds cost, curing time, and a compatibility review. None of the three options is free. The decision should compare schedule, warranty, and risk, not just first cost.
2. What product research and verification should the design team require?
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Verify the current technical data sheets, not a sales summary; confirm that Product B's 90% limit applies to this adhesive, this substrate, and the ASTM F2170 test method at 40% depth. Ask both manufacturers for a project-specific written statement. Check Product B's open time, trowel notch, cure time, VOC, and warranty in a library application. Get the 14-week lead time in writing, including the order cutoff. For mitigation, verify the system's VOC and compatibility with the adhesive and slab, and require a mockup. Re-test RH after mitigation. Also confirm whether the 88% value is the highest reading or an average; one high reading can govern.
3. Recommend a course of action and describe how it should be documented.
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Recommend mitigation plus Product A if the added cost and cure time fit the 19-week opening; it preserves the specified adhesive and avoids the 14-week lead. If mitigation cannot be completed within the float, present the owner with a written choice: accept the delay for Product B or approve mitigation with a schedule recovery plan. Do not let the contractor switch products by field direction. Issue a formal response with a comparison matrix, require revised submittals, and document the owner's decision in the OAC minutes. That way the warranty and schedule risk are owned by the party who chose the option.