Counterflashing is pulling away from
the chimney. In the top photo, expansion and
contraction have caused a failure of the caulk used to seal the
surface-mounted counterflashing to the chimney. In the bottom
photo, a too-shallow flange in the counterflashing has allowed
water to get behind the flashing when the brick gets saturated
in a heavy rain.
Install the counterflashing between
courses of brick as the chimney is being laid up.
The minimum width flange for counterflashing inserted into a
brick chimney is 1-1/4 inches.
For existing masonry, cut a 1-1/2-inch-deep kerf into a
mortar joint with an abrasive blade. Run a bead of caulk along
a 1/4-inch hem turned up on the back edge of the flange, then
slide the flange into the kerf. The hem will compress slightly,
holding the flange in place. Finally, caulk the top of the
flange where it enters the kerf to keep excess water out.
Failure of caulk between stucco and
flashing. Don't depend on caulk or roofing cement to
keep water out of a crack anywhere on a roof, especially if the
crack is between dissimilar materials, which expand and
contract at different rates. Caulk has its uses, but it should
not be relied upon as the primary barrier against water
that permit some movement. When stucco
will be used above counterflashing, the counterflashing should
be installed first, behind the stucco, and the felt
underlayment should be lapped over the counterflashing.