Cutting a reglet for new chimney flashing installation or repair.

Chimney flashing is really not that complicated. The problem is that many roofers just don't take the time to do it right.  I often find when investigating leaks or repairing and replacing chimney flashing is that if the installer had just taken a little more time to do the job, it would have lasted as long as or longer than the life of the roofing shingles.

The chimney reglet, sometimes called a raggle, is a groove cut into the masonry mortar to accept the top of the chimney counter flashing. For the longest lasting job, the reglet should  be cut the full width or thickness of the mortar joint.

There are a couple ways to do this. One is by  using a small hand held grinder with a diamond tipped masonry blade. This is a fast way to cut mortar but can easily cut the brick and should only be done by an experienced professional. This method works very well on the new harder mortars that have been in use since the early 1900's. These mortars use much more Portland cement than in the old days and are very hard to cut with hand tools.

For older buildings, and those with historic significance, the use of a diamond grinder should be avoided. Old masonry bricks were much softer than those used today and if the surface is nicked or cut, water is easily absorbed into the brick causing rapid deterioration. To remove the mortar of these softer walls it is best to use a hammer and stone chisel.

The mortar joint should be cut long enough so that the chimney counter flashing will lap, or extend past the edge of the piece below. Three inches of lap is usually sufficient to make a water proof wall flashing. It should be cut deep enough to accept the top lip of the flashing without binding or holding the flashing away from the chimney. And it should aways be cut as straight as possible, especially the bottom edge (or top of the brick line), so the flashing sits tight to the brick and does not buckle when fastened to the joint. The rear of the joint should be kept high enough off the roof, approximately 3 inches away on a perpendicular line, to allow for installation of the shingle flashing.