If there is a large hole through the wall, patching      
plaster will not stick. Two methods can be used:    
           

Method 1:
1. Mark a rectangle on the wall which includes the hole.    

2. With a knife or key hole saw cut out the rectangle       
being careful not to break it.                             

3. On a scrap piece of plaster-board, copy the section of   
the wall.                                                   

4. Then mark a frame about 2" wide around the section of    
wall.                                                       

5. After cutting, remove the paper on one side and the      
plaster from the frame around the patch. The 2" frame of    
paper will stick out like an ear all around which will      
hold the patch in place.                                    

6. Spread patching plaster around the edge of the hold      
and around the edge of the patch. Put the patch in the      
hole and press the paper ears into the plaster and hold     
it while it sets.                                           

7. Sand lightly and paint.                                  

 
Method 2:                                        
1. Cut a piece of metal plaster lath or heavy screen        
larger than the hole.                                       

2. Fasten one or two wire ties to the lath and insert       
through the hole.                                           

3. Pull the lath up behind hole and wire to a stick of      
wood placed across the hole on the front side of the        
wall.                                                       

4. Moisten the edge of the hole and spread a base coat      
of patching plaster to within 1/8" of the finished          
surface. Roughen the surface with a stick or nail so the    
finish coat will stick.                                     

5. After the base layer is dry, remove the stick and        
clip the wires close to the surface.                        

6. Trowel on the finish layer being sure it is flush with   
the wall surface.                                           

7. Let it dry well and then paint.                          

8. If the patched area is large, apply a coat of sizing     
before painting.                                            

This article was written by Anne Field, Extension           
Specialist, Emeritus, with references from Michigan         
Extension bulletin Wall Repair and Fasteners.