Here is a excerpt from the book called “Windows and Doors” by “Scott McBride” about door repair. Fixing door problems could be tricky, hope this article helps our users with DIY Door repair

To prepare a crater for filling, remove all loose material. Blast the crater with compressed air if you have a compression.  To anchor the patch, drill a series of ¼ in diameter holes radiating from the crater into the surrounding wood.  Drill the hole, about ½ in deep but be careful not to drill through the door.  Filler squishes into these holes and hardens into little tentacles that hold the patch in place.

Epoxy filler is activated by mixing a small quantity of hardener with a large quantity of resin: follow the directions carefully for the correct proportions.  Mound the filler above the surface, and then sand it flush when it dries.  For a head start on sanding, use a Surform tool to remove the bulk of the excess material. 

A Surform tool works best when the epoxy is still in a semi hardened state.  This lasts for only a few minutes before the filler hardens completely, so be ready.  Don’t try to sand partially hardened epoxy—it will just clog your sandpaper After about 20 minutes, sand the area with 50-grit paper and finish with 80-grit to 120-grit paper, depending on the desired smoothness.  Finish the surface with the appropriate primer and paint.

You can do other repairs with epoxy, as well.  For instance, when you move a lock from one side of a door to the other, use epoxy to fill the old lock bore or mortise.  To reduce the amount of epoxy required, embed chunks of wood within the patch.

You can also use epoxy to repair a door that has been damaged by decay.  Rather than  excavating all traces of decay, firm up the softened wood with liquid consolidator.  This form of epoxy has a syrupy consistency that allows it to soak into decay-softened wood.  Thick-bodied epoxy filler is used to rebuild missing areas after the consolidator is applied.  To improve the chemical adhesion between the filler and the wood, apply the filler as soon as the consolidator becomes tacky. 

When building up an edge or a corner, you need to anchor the repair to the door especially well.  Drive screws or lag-bolts into the door with their heads sticking out.  The farther the screws extend into the patch the better, but don’t let them extend beyond the projected face of the door.  Apply epoxy to the area, then  grind the patch back to its final dimension after the filler handles.

Installing wooden patches

A wooden patch, sometimes referred to as a Dutchman, is a good way to make a surface repair in a door with a natural finish.  The repair won’t be 100% invisible, but it’s the next best thing to a new door.  A well-executed Dutchman can even add character.

To excavate the damaged area, use a router with a straight bit.  Insert a guide collar into the router’s base plate, and then use a plywood tern-plate to guide the collar.  Make successive passes with the router, lowering the bit about 1/8 in. for each pass until you reach the necessary depth.  After routing, remove the corners of the recess with a sharp chisel.

To make the patch, select a piece of wood with matching grain and color.  Rip the patch to the correct width on a table saw, and then cut it to length.  The thickness of the patch should be slightly more then the depth of the recess.  Taper the edges of the patch ever so slightly with a sanding block, just a hair smaller than the recess below the surface, so that the patch will be tightly seated.

 Apply  glue to the bottom of the recess and the bottom of the patch, but don’t glue the edges.  Then clamp the patch for at least eight hours.  To trim the patch down to the surface of the door, start by planning across the grain.  Planning with the grain may tear the wood.  When you get to within 1/16 in. of the surface of the door, switch to a sanding block or a power sander to finish up.  Completely sand any squeeze-out before staining or finishing with a clear coat.

Sometimes you need to patch hinge gains when you reverse the swing of a door (or when the carpenter goofs in the first place).  The patch needs to be only about 1/8 in. thick, but such a thin wafer of wood will warp as soon as you apply glue to one side.  It’s better to leave the patch ½ in. to ¾ in. thick.  After the glue dries, saw or plane off the extra thickness.

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