Paints, Coatings, Liquid-applied Membranes: Understanding options for roof repairs and retrofits

Two basic approaches to repair
It is useful to think of a project in two distinct phases:

  • repair/detailing; and
  • field coating.

It is often best not to use a liquid-applied repair solution if a conventional one is available. There are numerous reasons for this.

  1. Often, a warranty may still be in force, and will be voided by alternative repairs.
  2. Using in-kind materials, such as polyvinyl chloride (PVC) patches for a deteriorating PVC roof, may make permitting easier or even unnecessary.
  3. If the roof already has two layers, it is much easier
    for a code official to treat a coating as a maintenance item; even a liquid-applied membrane may be treated as a ‘coating’ in this light.
  4. There are specifically engineered and very durable components—such as standpipes, scuppers, solar panels, and drains—designed to install easily and more quickly.
  5. In-kind repairs are often more aesthetically pleasing.
  6. Use of historically correct materials may be required on all visible portions of the roof.

Once in-kind repairs are made, the field coating phase is greatly simplified and can be accomplished in accordance with the manufacturer’s standard published instructions. This may involve redundant detailing if deemed a condition of warranty or the desire to extend service life.

Of course, there are other cases where liquid-applied repairs make the most sense. They include cases where:

  • a roof with a collage of materials of different types and ages requires uniform appearance—in-kind repairs may require several trades, flipping the economic advantage to using all-liquid products;
  • a roof is out of warranty, or original materials are unavailable;
  • the owner wants its own maintenance crew to make the repairs—often a significant advantage with coatings over other forms of prepared roofing;
  • the old roof contains materials no longer accepted due to safety or health concerns; and
  • the assemblies are obsolete, or simply failed to perform in the first place.

Generally, liquid-applied details involve the use of one layer of reinforcing fabric (polyester, glass mat, or a hybrid of the two), overlapped so at no point of the detail is there a butted joint leaving an unreinforced site. Illustrations are typically available from the manufacturer in architectural format, but they are all very much the same. The coating may be used all at once, in a wet-on-wet approach as is common in reactive systems (e.g. urethane, polyether, or polymethyl methacrylate [PMMA]) or in three courses utilizing coating, fabric, and coating.

The reinforced detail will typically be at least 650 µm (25 mils) thick, and have a total tear strength of at least 3.5 kg/cm (18 lb/in.). When using unreinforced liquid details (e.g. liquid flashings), the total tear strength will be similar but will require a special grade product and thicker application, perhaps 1525 µm (60 mils) or more. Consequentially, liquid flashings are often solvent-based urethane, styrene ethylene butylene styrene (SEBS), or other materials that are both tough and flexible at low temperatures.

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