This laboratory test method can be used on multi-ply roofing and waterproofing systems to measure, classify, and count the voids between felt plies, between insulation layers, and between the membrane and insulation layers. Voids between the felt plies or between the membrane and insulation layer in multi-ply systems can be the seeds for future blisters.

In one-ply systems, this test method can be used to count and measure the voids in the adhesive in laps and, in adhered systems, in the adhesive between the membrane and the insulation. Voids in the lapping adhesive can be the source of leakage while voids in the lapping adhesive or in the adhesive between the membrane and insulation can be the seeds for future blisters.