Exposed Aggregate

Many side sewers in Seattle are constructed from concrete pipes. Concrete pipes are made of a mixture that includes cement and aggregate (rocks). As the interior cement wall erodes away, the aggregate becomes exposed and continues to erode. This is the most common and critical defects in a side sewer pipe.


Routine inspection

Minor exposed

Minor exposed aggregate.

The rocks are just beginning to show through the interior surface of the pipe; will have little to no effect on the function of the pipe.

Inspect three to five years after the original inspection.

Routine inspection

Moderate exposed

Moderate exposed aggregate.

The surface of the interior of the pipe is bumpy from the rocks and porous; will likely not impact the function of the side sewer but the structural stability is decreasing.

Inspect every one to two years and begin planning for repairs.


Severe exposed

Severe exposed aggregate with holes.

These pipes are considered to have reached full structural failure even though flows may still be able to travel through or seep out of the pipe.

Replace as soon as discovered.