counterflashing?

[George]

Our house is built of more-or-less solid cement blocks (c 1920, we think.) It has a lower roof that butts against the main wall, which joint I need to flash. My plan for the counterflashing is to cut a slot along the blocks, to accept the 'top' of some rake edge, with the other face of the rake laying down over the step flashing.

A single kerf fits the rake edge, but snuggly. I can go with that, and bed the rake in (silicon?) caulking. Or, I can cut a wider slot (1/4-1/2"), and bed the rake edge in mortar.

Any thoughts on the pros/cons would be appreciated.

Thanks, George

[krw]

How clean of a slot can you make? I was thinking something along the lines of rubber rope (think screen spline) to mechanically wedge the flashing, then use the silicone to seal that in. ...just a thought from a DIYer.

[George]

I don't think there's room for a spline, even a thin one - the slot is cut w/ a masonry blade on an angle grinder, so it's _mostly_ only as thick as the blade. (There are places where it's less than perfect straight, I have to say.) As far as wedging it, I have to cut about an inch off the back of the embedded side of the rake. I plan to leave tabs in that, and bend those over to wedge it in.

[krw]

You mentioned cutting a wider slot but perhaps that's not such a good idea now.

If I'm picturing your setup, you want to fold the tab over to wedge it in. The folded tab would then expand and lock it into the block and resist pulling. What you propose sounds like it'll work to hold the flashing. I was just thinking about something a little stronger mechanically, so the silicone wouldn't pull out. I'd use the silicone on the tab side (if I'm getting the picture right) so it helps the wedge/tab hold. Let it set up before you bend the flashing over.

[Mk]

Clarify how you intend to cut along the block. You're not really thinking of cutting into the block, are you?

[George]

Yes. In fact, the first cut is already done. As noted, the blocks are solid. Not cored.

[RicodJour]

This is how it's supposed to be done:

The top bend 'barb' locks the flashing into the reglet (that's the term for the slot you cut). Another way to lock it in place is to roll up small pieces of flashing that will just fit into the reglet with the counter flashing in place, and then use a cold chisel or old screwdriver to push the little roll into place, with a hammer if necessary. Everything gets caulked in place with polyurethane caulk.

R