Roof Coatings: Restoration or Repair?

Roof coatings typically fall into two groups: Repair and Restoration. Both use similar products, but the objective is different. Restoration will include repairs, but the objective is to avoid roof decay, allowing your roof to live longer.

Coatings for Roof Repair
Many coating systems exist for metal roof repair. Regardless of how many layers, or plys, they contain they are comprised chiefly of elastomeric resins of one kind or another (e.g. acrylic, butyl, polyurethane, silicone). An elastomeric coating has elastic properties, and can stretch and return to its original shape without permanent deformation, accommodating small shifts in roof panels such as those caused by changing temperatures. Each polymer type has advantages and disadvantages:

• Acrylic: Low cost water based coatings are easy to use and clean up. They are permeable which allows moisture to pass through the coating.
• Butyl: Highly resistant to moisture and vapor transmission, these coatings are typically used over asphalt built up roofs.
• Polyurethane: Providing greater ponding resistance, these coatings are also highly resistant to moisture and vapor transmission. Typically used over metal, single ply (PVC, TPO), and EPDM. They can also be used on modified bitumen.
• Silicone: A popular alternative to polyurethane for use over polyurethane foam.

Coatings for Roof Restoration
Used alone, an elastomeric coating system represents a patch on the entire roof, thus avoiding the main problem with small patches - moving leaks around. However, in a roof restoration system consideration must also be given to protecting the deck. Typically this is done with two additional products:

• Sealer: Made from the same elastomeric polymers described above, this product is applied in a thick layer to seal seams, prevent ponding, and protect the metal or wood deck underneath the roofing material.
• Cathodic Protection: A coating containing metals such as zinc or aluminum to act as sacrifical anodes, extending the life of the steel fasteners or metal deck.
  

Roof Maintenance: Restore Don't Repair

Various roof maintenance options can have radically different outcomes. Typical options include:

1. Do nothing. No action or expense is required. Outcome: deck (metal, wood, etc) corrodes and an expensive re-roof is necessary.
2. Repair roof with patches. A roofing contractor is called and goes up on the roof with a bucket of tar, or the equivalent. Outcome: leak is initially stopped, but now water accumulates in a new area so every year more patching is necessary, deck eventually corrodes and an expensive re-roof is again required.
   
3. Restore. The old roofing material is renewed. Re-coating a metal roof is analogous to putting new roof tiles or shingles on a conventional roof. Outcome: leaks are stopped, deck is protected for the life of the coating, tile, or shingle.
   

The interested reader is referred to systems such as Iron Sentry for restoring of metal, built up, or single ply roofs MCA for clay roof tiles, and Elk for shingles.