How to Test Waterproofing at Elongation

Cut out a square piece from your waterproofing membrane with a pair of scissors. The square piece must measure 3-by-3 inches. Place the membrane on a flat surface covered by a sheet of white paper.

Place a dot on the paper directly over the top-left corner of the membrane for your starting mark. Place the tip of a cigar box or a square cookie tin on the membrane's left side. Use your left elbow to apply pressure to the box and hold the membrane's left side firmly in place.

Grab the membrane square's right side firmly with your right hand and stretch it to the right, without applying too much pressure. When you see the membrane square's top and bottom sides bend inward, place a dot directly above the top-right corner of the membrane.

Measure the distance between the starting mark and the mark noted in Step 3 with a ruler. The distance should be in inches.

Subtract 3 inches -- the membrane square's initial length -- from the distance noted in Step 4 and divide the difference by 3 inches -- again, the membrane square's initial length. Multiply the quotient by 100 to calculate the membrane's percentage of elongation: This is the elongation the waterproofing membrane can withstand until it becomes deformed and unsuitable to use.