lime scum

例句：

1. 1. The builders used lime to level the ground before painting.
   建筑工人使用石灰来平整地面，然后进行粉刷。
2. 2. The old house had a layer of lime scum on its roof.
   这所旧房子的屋顶上积了一层石灰渣滓。
3. 3. The painter was careful not to leave any lime scum on the walls.
   画家小心地不把任何石灰渣滓留在墙上。