Measure up the edges, corners and internal joints that need to be waterproofed. Then cut lengths of reinforcing tape to cover these areas. Paint a coat of waterproofing where the tape will be installed and then put the tape over the top of the still-wet area. Use your brush to flatten the tape out and push it into the corners. Then paint another coat over the top of the tape to reinforce the joint further. To finish, paint the rest of the surface and allow it to cure for at least 24 hours.