My slate roof has just been redone, looks like quality work by competent roofer but I am worried about the abutment flashing where my roof meets the next house's wall. He installed lead soakers at the abutment (which I think is right) but covered them with cement. I asked about lead flashing instead but he said because the abutment wall is rendered, cement flashing was proper. I am concerned about durability. How long will the cement last before cracking? Should I insist on lead? I assume that will come with significant extra cost which will be a challenge, so if the cement will last more than 5 years I'll take it. Adding a photo from last week that shows the soakers underneath, but the work is now fully completed, and the soakers fully "flashed" in cement.