Question
What is a fillet seal?
Expert Answer
A fillet seal is a wedge of high-strength waterproofing mortar formed at the junction where the wall meets the floor. This 90-degree internal angle is a common weak point for stress and cracking. The fillet reinforces this joint and, in Type A tanking systems, helps to smooth the angle so the waterproofing coating can be applied continuously without cracking. It is a critical detail in keeping a basement dry.
