SpecTips - Choosing a High-Performance PVC Roof Membrane –Thickness Over Scrim

PVC Roofing–Thickness Over Scrim

There are many factors that play into the weathering of a roofing membrane’s surface. Abrasions caused by windblown particles and foot traffic can be major contributors to a reduction in membrane thickness. That’s why PVC membranes with adequate thickness over scrim (reinforcement)can help to offset the dramatic effects of abrasion and general PVC aging.

What’s important to note is that not all thickness over scrim is created equal.

• A greater thickness over scrim could mean that the reinforcement fabric is not centrally located in the membrane,and therefore is more likely to be pushed through the bottom layer of the PVC. It is important to inspect a cut edge of membrane to ensure the scrim is centrally located in the membrane.
• Even if the scrim is centrally located in the membrane, the manner in which the layer of membrane over the scrim is constructed plays an important role. For instance, this is where all the UV inhibitors, heat stabilizers, and other weathering ingredients that are necessary for long-term performance are located. That is why it is important to select a PVC membrane that is constructed with a monolithic top layer. In the photos below, you see a comparison of two membranes, both with a centrally located scrim. The difference between the two is that one has a monolithic layer with weathering agents down to the scrim, while the other has two separate top layers, with the bottom of these two layers having had important chemicals eliminated. Removing these chemicals reduces the weathering layer, which leads to a negative impact on long-term performance.

SpecTip
In Part 1 of MasterFormat Specifications under the Quality Assurance Section, add verbiage to include, “PVC membrane shall meet the minimum performance requirements of ASTM D4434 and shall have one monolithic formulation layer above the reinforcement.”

Monolithic vs. Multiple-Ply



For more information about Monolithic vs. Lacquer-Coated Top Ply, click here.

For more information about membrane thickness, click here.