PVC Is To Asphalt Like Oil Is To Water

When considering reroofing options for commercial facilities, it’s important to keep in mind that not all “new” roofing materials are compatible with “old” materials. Case in point: PVC membrane roofing products are not compatible with asphalt-based products. Like oil and water, like Superman and Kryptonite, like a tuxedo and brown loafers, it’s best to keep these two materials away from each other.

If you’ve made the decision to replace or re-cover your old asphalt roof with a new PVC membrane, here are some common issues that can affect the quality of your new roofing installation:

  • Tear-offs of asphalt roofs often create dust that contaminates new membrane. To avoid this problem, consider the wind direction and take steps to ensure that dust blows away from PVC materials. Use a tarp on PVC materials that are placed near the tear-off so that asphalt dust does not get on the new membrane. Develop a work plan to make sure that asphalt-contaminated shoes or boots do not get on the membrane. And complete the entire asphalt tear-off before beginning the PVC installation.
  • Make sure that proper, compatible sealants are used on the new membrane. Many caulks, sealants, and pitch pocket fillers contain asphalt, and should never be used on PVC.
  • If your project involves re-covering the built-up roof rather than tearing it off, a suitable separator must be installed between the old asphalt and new PVC roofing systems. Insulation materials such as EPS or EXPS rigid foam (whether fanfold or board – as long as it has an approved facer) and polyiso foam board work well. At a minimum, Duro-Last® requires the use of one of our polyethylene separator sheets, either the Duro-Weave™ or Duro-Blue™ product.
  • If asphalt does come into contact with the new PVC membrane, clean it immediately, because it will “bleed” into the membrane and become impossible to remove. Never use a solvent to clean asphalt off the membrane. Solvents melt the asphalt and soften the membrane, making the problem worse. Instead, use cleaners like DeWitt’s Remove-It Citrus Spray Cleaner, Simple Green®, or a non-solvent based whitewall tire cleaner.

Follow these few simple steps on your PVC roofing project to get a secure, watertight installation that even Superman would have problems pulling apart.