I am re-building the exterior of my house, insulation, sheathing, CI, siding; and during the demolition phase (taking the existing masonite siding off and the deteriorating spray foam out), I noticed that the masonite siding is installed behind the brick chimney. This makes it pretty impossible to get off since it is nailed behind the chimney and the chimney is installed immediately next to it. 

My current plan is to cut the masonite where the brick is, leave it behind the chimney along with the spray foam, install the Zip board up against the masonite behind the chimney and then liquid flash the zip board to the brick of the chimney. This should seal the masonite in and prevent any water getting to it. Does this sound like an acceptable way of dealing with this? 

I’m interested to hear any other suggestions about how to deal with this situation. I can’t really think of any other way of dealing with it aside from removing the entire brick chimney which I am not going to do.