Fixing Hollow Doors

     Our laundry closet has hollow bi-fold doors.  They look nice, but they are kind of cheap.  The only solid area is around the outside edge.  The door knobs wouldn't look right placed on the edge, so they are centered on two of the doors where it is hollow.  It wasn't long before the knobs loosened.  Tightening the screw just pulled the layers of the door toward the center, dimpling the front and back surfaces.  I put a great, big washer around the screw on the backside of the door.  It helped, but recently the knobs have gotten very wobbly.
     I scouted around online for some fixes.  One person suggested spraying foam insulation into the door through the screw holes.  Once the insulation dried, this individual thought the hole could be re-drilled and the knob could be attached.  I had my doubts that foam would be strong enough to hold over the long haul.  I found a product made specifically for the situation.  It's a plastic sleeve, that goes through the door like a giant molly, called Knob Secure.  I also had doubts that Knob Secure was the best way to go.  I was looking for more support over a larger area.

Wobbly knob.

The washer fix that didn't last. 

The paint wore off and the hole was enlarged.

I sanded off the paint for better adhesion.  The inner box is where I cut a hole.  The outer box is where I placed a cover over the hole.

I put a screw drive through the door so the piece I cut out wouldn't drop into the hollow door.  I used a box cutter to make the cut.  Since the doors aren't much more than cardboard, the box cutter worked well.

The plan is to insert a piece of wood that is the exact thickness of the door hollow.  It is as high vertically as this opening, but it is longer horizontally than this opening.

This is the center support and the cover.  The centers are marked and drilled.  That's where the door knob goes.

One edge of the center support is cut off so it can be angled into the space.  I coated both sides of the supporting piece with Liquid Nails and inserted it into the door.  I used a wooden shish kabob skewer to line up the holes and center the support.

After the Liquid Nails on the insert set up, I glued a 1/4" thick piece of board over the hole.  I used a screw to attach the door knob that was 1/4" longer than the original screws.  I also added a small screw on each edge of the board.  Maybe that was over kill.     

     It's not a thing of beauty, but it has made the door knobs solid as a rock.  It's not possible to see the patch when the doors are open or closed.  One would have to sit on top of the washer or dryer and close themselves into the closet to see the repair.  Once I prime and paint the patch, it will be even less conspicuous.