Counter Flashing a Chimney

What You'll Need
4 inch grinder with masonry blade
Extension cord
Safety glasses

The installation of counter flashing against a chimney works together with the base and step flashing to form a waterproof system for your roof.  Not only will it prevent leaks but it will also extend the life of your chimney’s masonry. All you need to complete this project are a few tools and a little know-how.

Step 1 – Cut the Mortar Joint

To effectively install the counter flashing you’ll have to remove the mortar joint along the step flashing and create what is called a reglet. Use the grinder to cut a 1 inch deep slot into the mortar joint to install the flashing. Remember to follow the line of the step flashing in order for the water to drain away from the chimney properly.

Step 2 – Install the Counter Flashing

Once you’ve removed the mortar joint install the counter flashing by inserting it into the hollowed out joint, and bend it over the step flashing. It’s best to use a stainless steel metal or copper but never use aluminum.

Step 3 - Finishing Up

The flashing should be at least 4 inches wide to overlap the step flashing beneath.