'''Step 5:''' Compact a 15 cm wide and 10 cm high apron over the external and internal grooves.
====Leakage through a cracked foundation====
[[Image:weld mesh.jpg|thumb|right|150px|Weld mesh cut to fit foundation. Photo: © E. Nissen-Petersen, Kenya.]]
'''Problem:''' Water leaks through cracks in the foundation.
'''Reason:''' Soft soil under the foundation, insufficient reinforcement, poor mixture of concrete or improper curing.
'''Remedy:''' The leakage can be sealed by constructing a new foundation onto the old cracked foundation.
'''Procedure:'''
'''Step 1:''' Drain all water out of the tank and clean the floor.
'''Step 2:''' Fill all cracks with bitumen paste.
'''Step 3:''' Cut sheets of weld mesh to fit the foundation. All overlaps must be at least 20 cm and tied together with binding wire for every 10 cm.
'''
Step 4:''' Mix concrete with 1 part cement to 3 parts river sand and 3 parts of crushed stones (1:3:3). Compact a 7 cm thick layer of concrete onto the old foundation.
'''
Step 5:''' Lay the weld mesh on the concrete in the tank.
'''Step 6:''' Compact a second layer of 7 cm concrete onto the weld mesh in the tank.
'''Step 7:''' Compact a 1 cm thick layer of mortar 1:3 onto the concrete. Smoothen the plaster and press a coat of NIL onto the plaster the same day.
'''Step 8:''' The next day, compact a rounded apron into the joint between the new foundation and the wall.
'''Step 9:''' Keep the foundation moist and under shade for 3 weeks