Restoring roofs

Is your roof in good condition, should it be restored or does it need to be replaced?

By Bob Tomlinson

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Roofing conditions can be divided into four categories:

Good. Roof has a few, if any, leaks and it appears to be in sound condition. Schedule biannual inspections, usually in the spring or fall. Regular inspections are key to keeping it sound.

Maintain. Roofs with minor problems, such as bare spots on graveled roofs, open laps in the flashing membrane or deteriorated sealant at the counterflashing. Inspection team performs maintenance during regular inspections.

Restorable. Roofs that need more than minor repairs but can be returned to good condition with reasonable attention. Examples include a granulated membrane roof with surface cracking and loss of granules and graveled roofs with bare spots that require a new flood coat.

Replacement. Roofs with extensive problems and not worth the effort or cost to maintain or restore.

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Bituminous roofing systems

Most bituminous roofing systems have a sacrificial surfacing that protects the roof's waterproofing components. It's important to maintain the integrity of this weathering layer during restoration.

Stained, deteriorated surface of a granulated modified bitumen membrane system.
Stained, deteriorated surface of a granulated modified bitumen membrane system.

Most bituminous restoration coatings are applied cold and used at ambient temperatures. They consist of a bituminous resin, a solvent or water carrier, reinforced fibers or fillers,and sometimes a reflective pigment.

The two principle forms of bituminous roofing are built-up or polymer (APP or SBS) modified membranes. Systems that combine both are referred to as composite or hybrid. Three surfacings are available: granulated, flood coat with gravel or smooth (with or without reflective coating).

Type of bitumen

Before restoring a bituminous roof, it's necessary to determine whether the materials of construction are asphalt or coal tar. Here are some techniques to identify the materials.

Odor. When heated, asphalt smells like fuel oil. By comparison, coal tar smells like creosote wood preservative.

Solubility. Asphalt dissolves in petroleum solvents, such as gasoline, kerosene and lighter fluid. Coal tar does not. Take a cloth soaked in petroleum solvent and rub the roof vigorously. Asphalt transfers a heavy residue of asphalt to the cloth and feels tacky. The residue will be dark brown in the center and light brown at the edges. A similar cloth rubbed on coal tar becomes discolored, but does not feel tacky or transfer a heavy film. The cloth will be light to medium brown at the center and yellow at the edges.

Laboratory identification. Coal tar and asphalt can be differentiated using mineral spirits. Place a sample into a beaker of mineral spirits (the ratio should be 2 grams of material to 20 grams of spirits.) Asphalt quickly turns mineral spirits to deep brown. Coal tar gradually turns it yellow.

Asphalt and coal tar compatibility

Always apply coating evenly with a flat squeegee
Always apply coating evenly with a flat squeegee.

Five rules apply when bringing asphalt and coal tar together:

  1. Don't try to heat or mix asphalt and coal tar in the same kettle.
  2. Don't use the same tools to apply asphalt and coal tar unless they are cleaned between uses.
  3. Don't "gravel-in" a coal tar and felt roof with asphalt.
  4. Don't use asphalt as the interply bitumen in a coal tar/felt membrane construction. Don't use coal tar as an interply bitumen with an asphalt saturated organic felt in a roofing or waterproofing system.
  5. Repair coal tar roofs with coal tar based repair compounds and asphalt membranes that use asphalt-based materials.

Substrate preparation

Follow these steps to prepare the existing membrane and substrate before applying the restoration coating.

Power broom or vacuum the membrane surface to remove loose aggregate, dirt and debris. If the membrane is installed over an easily compressible substrate, such as fiberglass insulation, vacuuming is recommended. Vacuuming does less damage to the existing membrane. If a power broom is used, remove any remaining dirt with a high-velocity leaf blower.

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