Q.: For epoxy injection, how do you achieve surface seal on the outside of a below-grade wall?
A.: Quite often, you can't achieve a surface seal on the back side of walls. However, you can still inject the crack (about 0.01 inch or wider) with good results using an epoxy paste. Use a nonsag paste (ASTM C 881, Grade 3 nonsag consistency) that penetrates the crack but still has adequate nonsag properties so it doesn't run out of the crack's unsealed face. Choose a Grade 3 paste with the consistency of toothpaste or mayonnaise. If it's too thick, it won't enter the crack; if it's too thin, it runs out the crack and won't appear at higher ports.
Because the epoxy is a paste and not a liquid, a few variations in injection techniques are required: a) space ports as far apart as the wall is deep, b) inject at every other port, then return to inject in-between ports, and c) use higher pressures to move the paste through the pumping system and hoses or mixing heads into the crack.