Answer by  
                                                                                          AnnaTeague (806)
                                                            
                          
                          
                                                          The technique is called point and tuck.  First, clean out the crumbling mortar between the blocks.  Mix new mortar according to package instructions.  Using a narrow point tool, fill in the cracks with mortar, pushing it in as far as it will go,  Smooth the edges and remove excess mortar.