Silicone sealant applied with brush
Technical Bulletins

Watch out when using just any sealant! Silicone Roof Sealant and understanding its benefits

January 2, 2024
Learn about Silicone roof sealant and repair products. The quality, benefits, and uses.

Silicone roof sealants are quickly gaining popularity for addressing roof repairs


Silicone’s use as a roof coating has been strong over the past decades and continues to gain popularity. As these coated roofs age, maintenance is needed. For sealing penetrations, detailing new flashing curbs and general repairs, understanding what sealants are compatible with the existing coating is extremely important. As of this writing,

the only sealant that is fully compatible and recommended for use over silicone coated roofs is a silicone sealant.

Other sealants or flashing cement commonly used in the roofing industry will not adhere to silicone. Although you may have doubted the saying “only silicone will stick to silicone”, it happens to be true. The need for a compatible sealant to maintain and repair existing silicone coated roofs has been one of the forces driving the popularity of silicone sealants in the market.

Silicone sealant has many unique properties making it advantageous to use. One is its ability to bond to several different roof substrates, most importantly: silicone coated roofs. Another is its ability to resist ponding water. Other benefits of silicone sealant include high elongation, long-term durability, and resistance to UV degradation. This means the sealant will not chalk from exposure and is resistant to ozone, aging, weather, and extreme temperatures. Not many sealants can claim these attributes.  

A Silicone-coated flat roof


Because of its high performance characteristics, Silicone sealant may seem like the ‘go-to’ repair product for use on all roofs, but it does have some drawbacks. The major one is using silicone sealant on non-silicone coated roofs limits the type of coating that may be applied over that roof in the future. This is because if a silicone sealant has been used for repairs, only silicone will adhere on top of it. This limits the building owner’s options for other coating technologies, unless the silicone sealant is removed first. This situation may or may not be advantageous to the building owner and their roof maintenance budget.

Silicone sealant offers good cured film physical properties, with most industry leading products having between 200% and 500% elongation, and 120 psi to 260 psi tensile strength. However, there are non-silicone sealants in the market such as SEBS thermoplastic rubber, acrylic, urethane and SBS modified asphalt with better properties and similar advantages that allow other coating chemistries to be applied over top so building owners are not limited in their options. There is a case for using all of these except when the roof is already silicone-coated.  


Prior to the application of silicone sealant, all surfaces should be dry, clean, and free from dirt, dust, rust, chalky residue, oil, grease, and other foreign matter.  Perform an adhesion test if unsure of an application. Wiping silicone coated substrates first with a fast-evaporating solvent such as denatured alcohol may improve adhesion. Damp surfaces may be temporarily sealed but all standing water should be removed first.


When repair and maintenance are needed on an existing silicone coated roof, 671 Karna-Seal is the product of choice! 671 Karna-Seal is a single-component, moisture curing, 100% silicone roof sealant that offers excellent UV resistance, flexibility, and tensile strength that resists weathering, hardening, chalking, and cracking. 671 Karna-Seal is intended to be used to make repairs to roof substrates previously coated with 670HS Karna-Sil Ultra silicone or other silicone coating. 671 Karna-Seal also offers excellent adhesion to modified bitumen membranes, metal, *aged single-ply membranes (TPO & PVC ), EPDM, Spray Polyurethane Foam and concrete.    


  1. Resists permanent ponding water
  2. Application by brush
  3. Bonds to several different roof substrates
  4. Low VOC, low odor
  5. For horizontal and vertical use, will not sag
  6. Rain safe in one (1) hour
  7. Ready to use, no mixing of components
  8. UV stable, may be left exposed
  9. Excellent weather resistance & durability

  • Note: TPO and PVC membranes should at least be 4 years old before using this product.
Check out our Silicone sealant!

The Karnak Team

Since 1933, our team at KARNAK has been dedicated to producing top-quality sustainable roofing and building solutions that protect and extend the life of building envelopes while reducing environmental impact. As a family-owned and certified woman-owned business, we pride ourselves on our commitment to quality, durability, and personalized customer service. We specialize in liquid-applied roofing systems, repair products, and comprehensive support through detailed documentation and our Q Applicator Program for contractors.

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