Concrete walls develop holes from water when the soil pressure behind the wall causes cracks to develop, which continue to break apart. The amount of time it takes to fix a wall with holes depends on how serious the damage is and how many holes there are. To get started, you need a hammer, safety glasses, a cold chisel, a screwdriver, mortar mix and a trowel.
Remove loose mortar and prepare the wall
Put on the safety glasses. For each hole that needs to be fixed, remove any loose or crumbling concrete pieces by tapping the area gently with a hammer. Use the hammer and chisel to chip out a dovetail shape by placing the chisel at the bottom of the hole and chipping away at a downward 45 degree angle until you reach the back of the hole. Repeat this step, except this time place the chisel at the top of the hole and chip away at an upward 45 degree angle.
Pack the hole with mortar
Using the screwdriver, scrape out any remnants of concrete or mortar. Pack as much mortar mix as you can into the dovetail shaped hole. The dovetail shape should help to keep the mix secure.
Clean and smooth the wall
Use the trowel to smooth the area. Clean up the surrounding area, and remove any loose concrete.