Sealing leaks is normally done by filling obvious leaks, cracks, and vertical seams above the water with a mixture of masonry, or portland cement & sand. Below the water, a special cement mixture designed for underwater use such as water plug is used.
Seals the seawall & stops erosion of soil from behind the seawall.
It is important to remember that sealing leaks causes more water pressure to build up behind the seawall and can cause the seawall to fail.
Sealing should only be done on seawalls that are structurally sound or have been properly repaired.
Grouting of vertical seams should fill the entire seam, including 1 foot below the mud line.
Drains are holes installed in a seawall, normally just above the barnacle line. After drilling a hole through the seawall, a short piece of PVC pipe with some type of filter cloth is installed.
In theory the relieving of water pressure from behind the seawall is wise.
Even the best of drains do little more than allow a slow drip. During a heavy rainfall a handful of dripping pipes do little or nothing to relieve the enormous pressure from the rainfall.
It should be noted that structural repairs do much more to prevent seawall failure.
Installing drains only, without structural repairs to the seawall, is considered a waste of money. The owner would be better off to conserve his funds until such time he can afford to do a structural repair to the seawall.
If only drains are to be installed, then the holes drilled through the seawall for the drains should be located at the vertical joints in the seawall panels to prevent structural damage to the seawall.