Base seal waterstop is ideal for flat pavement jobs such as runways, large containment slabs, etc. Base seal waterstop is by far the easiest waterstop to install... Simply lay the waterstop directly on the compacted sub-grade, place and finish concrete, and create control joint using saw cut or other method. The base seal provides a permanent, life-of-structure seal at the bottom of the joint. Base seal is suitable for construction, contraction (control), and expansion joints. Base seal should not be used on jobs that make interior wall transitions as the part is non-symmetrical and therefore cannot function correctly. For large hydrostatic head pressures (>50 foot) ribbed centerbulb should be used instead.