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About BlockFlash®


BlockFlash®* | The Complete Flashing Solution for Single Wythe Concrete Masonry Unit Walls

The perfect flashing system for CMU walls designed without a visible drip edge.

BlockFlash is a complete, embeddable flashing solution for managing moisture in exterior single wythe CMU walls.  It uses patented flashing pans to collect moisture in the wall and channel it to the exterior through integrated weep spouts.  Its included drainage mesh provides hundreds of clear pathways for water to flow around mortar droppings inside the block cells so it can be collected by the pans.

*Formerly known as "Blok-Flash"


  • Pans, integrated weep spouts and connector bridges made from high-density polypropylene 
  • 7" x 16" drainage mats made of 90% open weave polyester mesh
  • Factory-installed 90% open weave polyester mesh insect guards keep insects out of the block cells
  • Available for 6”, 8", 10", and 12" standard or insulated concrete masonry units
  • Snap-off connector bridge allows fast and easy pan installation in reinforced wall systems and at corners
  • Integrated bottom lip on weep spout makes it fast and easy to accurately align flashing pans
  • Drip spouts include a 45 degree drip edge to deflect moisture away from the wall and help prevent water marks and efflorescence
  • Sloped pans with integrated edge flanges catch and funnel water to the weep spouts


  • Complete flashing solution requiring no additional components
  • Lightweight, fast and easy to install
  • Requires no fasteners or adhesives
  • Applicable in all CMU wall flashing locations, including base of wall, parapet walls, and above bond beams, wall openings and structural steel members
  • Cuts labor and material costs associated with using membrane flashing in a multi-wythe course by approximately 50%
  • Eliminates the need for multiple architectural CMU sizes typical with through-wall flashing
  • Helps prevent costly call-backs and repairs due to damage caused by moisture in the block cores
  • Helps protect builders and designers from legal issues resulting from moisture damage
  • Helps prevent mortar damming and provides multiple pathways for water to flow to the flashing pan and out the weeps
  • Insect guard prevents damage related to insects entering the wall through the weeps
  • Maintains 1" mortar bond between courses and provides a flexural bond strength 10-times stronger than standard through-wall membrane flashing for greater wall integrity
  • Will not degrade, oxidize, or react with other common building materials
  • 40% pre-consumer recycled content of pans and drainage mat helps with LEED certification
  • Light weight and compact shape means convenient shipping, handling and storage

Brochures for BlockFlash®

Brochures for BlockFlash®
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Mortar Net Solutions Brochures

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News archive:
New Product From Mortar Net: Blok-Flash (Oct 03, 2012)
BLOK-FLASH® embeddable flashing device (Feb 09, 2010)

04 22 00 - Concrete Unit Masonry
07 10 00 - Dampproofing and Waterproofing
07 11 00 - Dampproofing
07 60 00 - Flashing and Sheet Metal
07 62 00 - Sheet Metal Flashing and Trim
07 77 00 - Wall Specialties