Bonding problems

Q: My company is using a flashing system that consists of a rubberized asphalt membrane adhered to concrete masonry back-up, and a stainless steel drip edge. During cold weather, we are having trouble bonding the rubberized asphalt to the concrete masonry and bonding the flashing to the metal drip edge.

What can be done to correct these problems?

A: Cold weather is a real problem with rubberized asphalt membranes. When temperatures drop below 50º F, the bond of the asphalt is greatly decreased. Because the membrane is not as tacky, it is often difficult to develop a good bond to cold concrete masonry.

Bonding is improved considerably by using primers that soak into the concrete masonry and have a slightly tacky surface that greatly increases the bond. I typically recommend using primers on concrete masonry, even in warm weather. However, they are especially important during cool temperatures.

Rubberized asphalt and the drip edge should be kept as warm as possible prior to use. A hair dryer or heat gun can be used to heat the surface during installation. Care should be taken to avoid damaging the membrane by overheating.

A heavy metal roller should be run across the surface of the membrane flashing immediately following its application to help promote a better bond. This action is especially important along the top edge at the concrete masonry, along the drip edge, and at any splice joints.

After rolling, the edge should be further sealed by applying the mastic recommended by the membrane manufacturer.