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Which Flashing Do I Use


We stock a lot of flashing products, including WR Grace, Fortiflash, and Prosco’s Fast Flash System by BEI.  Our installation crews and the general contractors we work with on a daily basis work hard to keep current on the latest technologies emerging in the fenestration and waterproofing area.  Frequently customers ask us about which is the best product to use.  This is a complex question and will depend on the manufacturer’s installation instructions, existing building envelope waterproofing, building exposure, consultant or architects design, etc. The most important thing to realize is that Compatibility is Key to Proper Window and Door Installation. 

Fast Flash Cartridge from Prosoco

For example some Vinyl windows and doors should not be installed with asphalt based flashing materials.  You should speak with the window and door manufacturer prior to using an asphalt based flashing material on a window with a plasticized nailing flange.  Grace has an excellent Technical Bulletin (#6) available discussing the difference and compatibility issues with their product lines when used with rigid vinyl and plasticized vinyl nailing flanges. If in doubt or you can get an answer, Butyl based flashing is better suited for installation of vinyl windows and/or fiberglass or wood windows with vinyl nailing flanges

Fortiflash Products Used in Marvin Window Installation in San Rafael, CA. Window Features Marvin’s Aluminum Nailing Flange and Brick Mold Casing.

If a flashing manufacturer produces their own installation sealant, it is recommend to use it when using their flashing or building paper.  For example: Moistop Sealant is produced by FortiFiber to be used with their flashing an building papers.

WR Grace does not make a sealant but provided test data stating which sealants are recommended or tested to work with their products.  Tremco (S500 and U1600) and OSI   (EP-1000) both manufacturer polyurethane sealants that are compatible with the Grace Vycor and Grace Pro Flashing lines. You can find Tremco’s Technical, Tremglaze U1600, Letter Regarding Grace Compatibility and Tremco S500 Silicone, Regarding Grace Compatibility letters at the respective links.

Tyvek House Wrap and Marvin SillGuard Pan Flashing used to Install a Marvin Wood Exterior Window
(Photo Prior to Backer Rod and Sealant Being Added)

In situations where building paper or a peel and stick flashing don’t make sense, won’t work, or cannot be used, there is another product that we feature for these situations.  Prosoco’s Fast Flash line of products are designed to replace traditional flashing methods and create a waterproof, breathable barrier when used to install windows and doors.   The Fast Flash product line is made of a number of components to provide a complete building envelope weatherization product line. Fast Flash is an STPE, which means it has a wider comparability range than Asphalt and Butyl based peel and stick products.

Storefront Window In Concrete. Sealant is a key component, since no flashing or peel and stick is used.

Regardless of which flashing product you decide to use, refer to both the window and door manufacturer’s product installation instructions, flashing manufacturer’s installation instructions, and sealant manufacturer’s installation guidelines.

Old Town Glass, Inc. is a window and door retailer and licensed glazing contractor based in Novato, CA.  We distribute a complete line of window and door installation accessories.  For additional information visit our website.


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