I had constructed 4" inch wall on the external wall on the first floor what prec

         According to my view you should finish the wall with plaster of coarse sand mixed cement mortar 1;4 on both side of wall.

       You can mix water proof chemical in mortar.

         This is due to salty water used the plaster and also salty bricks have been used during construction. Remove the plaster and do again with coarse sand plaster using water proof chemical in plaster mortar.

                                                     Thanks