Spray the mortar surface with water.
Remove any excess mortar with a chisel, hammer and scrub brush.
Put on safety goggles and protective gloves.
Mix a solution of nine parts water and one part muriatic acid in your container. Add the water to the container first before you add the acid.
Test the solution in an inconspicuous area first before you apply it to the mortared area. Let the solution sit on the surface for 10 minutes. Then spray the area with water. Muriatic acid can damage certain kinds of bricks and stones that are made with concrete rather than clay.
Wet the mortar with water.
Apply the muriatic acid solution to the mortar. You should see small bubbles react with the mortar as the chemical reaction occurs between the acid and the limestone.
Wash the area with water and reapply the acid solution until the mortar is fully dissolved.
Rinse the newly cleaned area with water one final time, and allow it to dry.
Apply a masonry sealant to the newly exposed brick.