Which of the following may not be used when waterproofing slabs below grade where compacted earth, non-reinforced concrete slab is in place before installation of the membrane?

• A. PVC Membrane
• B. EPDM Membrane
• C. TPO Membrane
• D. Bituminous Membrane

Answer: (A)

When waterproofing slabs that are below grade and buried under compacted earth, the membrane must withstand hydrostatic pressure and be robust under soil contact and backfill without relying on exposed seams. PVC membranes rely on heat- or solvent-welded seams and a clean, dry surface to seal reliably. Once soil is backfilled above the membrane, those seams are more susceptible to damage, contamination, and stresses, making reliable long-term performance difficult in this buried, backfilled condition. Bituminous membranes, EPDM, and TPO are generally better suited for below-grade use because they tolerate burial conditions, backfill loads, and minor substrate irregularities while maintaining watertightness. Therefore, PVC is not appropriate for this specific below-grade installation.