In This Article:
Counterflashing on a chimney is carefully bent back into shape so it can be adhered to the step flashing below.
2-3 (Basic - Intermediate)
About 1 Hour
Bruce W. Maki, Editor
There are supposed to be two types of flashing where asphalt shingles meet a chimney. The first is the conventional step flashing, which is seen in several of our roofing articles. There is one piece of step flashing for each row of shingles. The second component is called the counterflashing. This piece of metal is an upside-down "L" shape with the shorter leg embedded in the mortar between the bricks or cement blocks of the chimney.
But... I have seen many houses where the counterflashing was omitted. This means that the step flashing needs to be well bonded to the surface of the chimney, which is not easy.
The flashing on the sides of this chimney was not removed, just cut back slightly. The new step flashing needed to be seamlessly bonded to the old counterflashing. But the old flashing was quite bent and would not lie flat, even with adhesive.
The old counterflashing was bent away from the chimney and would not lie flat. This flashing was installed when the chimney was made, and is tucked into the mortar joint.
I tried something new: I put a pen under the top of the flashing...
...and tapped the flashing with a hammer.
This technique seemed to work.
I then hammered the top-most bulge, and below it...
... but some of the curl remained.
So I tried using a long (about 24") screwdriver.
Before you hurt yourself, read our disclaimer.
I worked from the bottom to the top, lightly hammering just below the screwdriver.
It seemed to work..
I applied some roofing tar behind the flashing.
It was very easy to push the caulk tube in too far and bend the flashing again. I found that using a long thin stick (such as a shim) to spread the tar was effective.
After I had applied a bead of tar deep down in behind the step flashing, I used silicone to seal the top of the flashing. (This is behind the chimney, at the new saddle... the other photos are on the sides where the existing roof meets the chimney.)
Roofing tar may be a better adhesive than silicone, but tar that is exposed to sunlight will degrade within a couple of years. Silicone can resist the sun's UV rays for decades.
I placed heavy cement blocks up against the flashing to hold it in place while the roofing tar dried. I left the blocks in place for a week, although a day or two would have been adequate. Placing cement blocks on a roof, right near the edge, could be a serious safety hazard if something were to knock off the block while a person was underneath. A safer method might be to clamp the block with a very long Quick-Grip type of clamp.
Another method would be to place some blocks of wood against the flashing piece(s) and use a band clamp (or a ratcheting tie-down strap) to hold the blocks tight to the chimney.
Note that the flashing method seen in the above photo is NOT the preferred method of installing flashing around a chimney. The homeowner mainly wanted a saddle installed to help shed water from the chimney area. Since I did not have access to a grinder with a diamond blade I was not able to grind out a narrow groove in the mortar joint and install counterflashing. While this is a less-than-perfect remedy, it is much better than the previous situation, and the counterflashing can always be installed later.