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Frequently Asked Questions

Below are some common questions and basic answers to assist you in your coatings project. Please note that these Frequently Asked Questions provide general guidance for projects covered under the standard product limited warranties. For certified contractors seeking information regarding requirements for enhanced system guarantees, see the United Coatings™ Liquid-Applied Roofing Application & Specifications Manual and the HydroStop® PremiumCoat Liquid-Applied Roofing Application & Specifications Manual, both available at

For reference purposes, several detailed cut specifications are attached for certain common applications over standard approved substrates using some of our most popular coating products. GAF offers many other coating product solutions, so please visit for additional product information, including product data sheets and technical manuals. If you have specific questions or you don’t see an answer to your questions here, please reach out to Technical Support Services for additional information or detailed requirements. To help assure a successful installation, please read the full application instructions available at or on the product packaging prior to starting any project. For additional information, assistance related to a specific substrate, or application questions, reach out to GAF Technical Support Services at or call 877-423-7663, option 4

What kinds of roofing material may be coated?

There are many suitable substrates for GAF roof coatings. An abbreviated list with common substrates appears below. Only structurally sound roofs or substrates should be coated. Roofs must have positive drainage with no moisture trapped in the roof assemblies. Roof substrates must be clean, completely dry, and free from any foreign matter.

What impact does the weather forecast have on my project?

Good weather is important to a successful coating installation. Specific installation temperatures vary by product, but our popular acrylic coatings require temperatures of 50⁰ F and rising. All substrates must be dry, so morning dew must have dried and the weather forecast must include no rain for 24 hours to help assure the newly installed coating dries properly.

Can I coat asphaltic roof shingles?

No. GAF does not recommend coating asphaltic roof shingles.

Can I coat over a roof with an existing coating?

Generally speaking, water-based acrylic coatings can be recoated with other water-based acrylic coatings, such as GAF’s Roofshield, Roof Mate or Hydrostop® products. Acrylic coatings can NOT be sprayed over silicone coatings. Additionally, asphaltic membranes coated with fibered aluminum coatings are not acceptable

substrates and the fibered aluminum coating must be removed prior to installing any GAF liquid-applied roofing product.

How do I prepare an existing roof surface to be coated?

Roof substrates must be clean, completely dry, and free from any foreign matter. Examine the substrate to receive new roofing and conduct test patches to verify adhesion of coating prior to start of work. Check for any damaged roof membranes, including all flashings and penetrations, and repair before coating application commences. Priming of the substrate may be required.

Can I coat over existing Kynar®-finished metal roofing?

Kynar®-finished metal panels and coping require special preparation prior to recoating.

Can I coat over penetrations or edge metal to give my project a finished look?

That depends, remember surfaces must be clean and dry. Any rust, or residual sealants (including plastic roofing cement) should be removed and/or encapsulated to assure proper adhesion. Small areas of rust may be pretreated and encapsulated prior to application of coatings. See the attached Cut Specification for compatible product options.

How do I know if I have enough material installed to obtain the desired limited warranty coverage?

The Cut specification contains application instructions (in the chart below) which gives you both a "wet mil" application rate and a "Gallons per sq." (100 sq. feet) measurement.

It’s possible (easy) to install too much material (and run out) and too little material (and risk not obtaining the desired roof protection). Below are two best practice tips:

  • Use a different color base coat and top Installing white on white makes it hard to tell if you have adequate coverage and an even application.
  • Using a wet mil gauge to measure the amount of coating as you are

Can I roll coatings or is a spray application recommended?

Both are acceptable application methods. Because rollers may absorb coating, be sure to plan for extra material needs.

What type of roller cover should I use?


  • On smooth surfaces 3/8" nap
  • On rough surfaces ½" to ¾" nap


  • 1"- 1 ¼" for all coating products

What Type of sprayer should I use?

There are several factors to consider when selecting a sprayer, including the thickness of the product you will be using and how you will be dispensing it. For small to moderate sized projects using GAF’s acrylic coatings, the Graco GH 300 (or equal) is a suitable option. Always be careful when using a sprayer to avoid damaging surrounding materials. A roller may be more appropriate for smaller areas. See the chart below for tip recommendations

Am I required to flash the seams on an existing roof membrane?

That depends on the substrate and the condition of the seams. All flashing requirements for seams and penetrations are included in the attached Cut Specification.

Do I have to prepare the substrate prior to installing the new coating?

Yes. Coatings will not properly adhere unless the substrate is clean and dry. Cleaning instructions appear on the attached Cut Specification. Refer to the below reference for Test Patches:

Do coatings have a shelf-life?

Yes, for best performance and to be eligible for coverage under GAF’s limited warranty only use coatings during the applicable shelf life set forth on the product label or container (usually between 12-18 months from the date of manufacture, provided the materials have been properly stored). Remember, improper storage can shorten product shelf life

How do I dispose of unused materials?

Always dispose of roof coatings (contents/container) in accordance with local/regional/national/international regulations. For more information on GAF’s coating products, see the Safety Data Sheets available on

What does GAF’s limited warranty cover?

GAF warrants that its products will not leak as a result of a manufacturing defect for a limited time period, which depends upon the amount of product installed, provided that the product is installed in accordance with published application instructions and during the shelf life indicated on this label or container. During the applicable warranty term only, GAF will provide replacement product for that portion of the product that leaks as a result of a manufacturing defect or, at its sole option, the cash value of such replacement product. GAF’s MAXIMUM LIABILITY is the original cost of the product only. There are no other product warranties, express or implied, including any implied warranties of merchantability or fitness for a particular use. GAF is not liable for any consequential or incidental damages of any kind, including but not limited to interior or exterior damages.

Other exclusions may apply. See Limited Warranty on GAF Liquid-Applied Roof Coatings at for complete coverage and restrictions.

Additional products and system constructions as well as additional Limited Warranty and Guarantee options for Certified contractors are available. Visit or email or call 877-423-7663, option 4 for additional information.

Below are just a few common applications and detailed Cut Specifications over common substrates.

Don’t see your desired products detailed below or need project assistance? Email: or call 877-423-7663, option 4.

*application rates vary based on substrate conditions. When estimating order quantities, we recommend a minimum additional 20% for typical applications. Aged asphaltic substrates may require 25% additional materials.

* * In select areas of the country GAF Silicone Products may be labeled "distributed by GAF" and contain a reference to "Lucas 8000 or Lucas 8500"

HydroStop© Acrylic Coating Over Asphaltic Membranes

HydroStop© Acrylic Coating Over EPDM Membrane

HydroStop© Acrylic Coating Over Galvanized Metal

GAF© Silicone Roof Coating Over Asphaltic Membranes

GAF© Silicone Roof Coating Over EPDM Membrane

GAF© Silicone Roof Coating Over Galvanized Metal