With a handful of tools, a little bit of know-how, and this guide, you will be able to fix unsightly holes in the hollow core doors that are common in the United States as well as cracks in solid wood exterior doors.

The most common way to fix a door is to use a quick expansion filler to fill the space in a hollow core door and then sand it down and paint to match the existing color. Solid wood doors, on the other hand, can be fixed using string, glue and putty, borrowing an old trick used to fix wooden boats.

Before we jump into a step-by-step guide to fixing the holes in your door, let’s take a look at some of the important features of doors as well as the common construction methods for these household barriers.

Solid vs. Hollow Core

There is a wide variety of doors that are utilized in both indoor and outdoor situations, although, regarding construction, most doors fall into either hollow core or solid styles.

It is a good idea to understand what these terms mean, so you know what type of doors your home has.

Solid Core Door

As the name implies, these doors are constructed from solid pieces of wood, although they are rarely made of just one single piece of wood. More often, they are built out of several pieces of wood, joined together in a panel style and hung within a frame.

These have long been the standard for household doorways, and they have a number of benefits over other designs:

Hollow Core Door

In the past 20 years, hollow core doors have continued to replace solid doors for home interiors for a number of reasons. These doors, while not exactly hollow, utilize empty space to cut down on cost and weight. Thin front and back panels, usually a wood or a fiberboard, sandwich strategically placed wood blocks or honeycombs made of either plastic or cardboard. This core is what gives these doors their strength and rigidity.

Hollow core doors have gained popularity, especially in North America, for a number of reasons:

  • Lightweight
  • Inexpensive
  • Easy to install

Design Styles

Now that we understand the basic construction techniques behind doors, it is worth taking a look at the two most common design styles that are used.

  • Panel Doors. They are commonly used in households thanks to their classic look. These doors are characterized by three or four horizontal “rails” and three vertical “stiles”, with thinner panels filling the space between them. Decorative molding is often used to accent these traditional doors.
  • Flush Doors. As opposed to the panel design, flush doors are simple, unadorned slabs and are the other most common style of interior door. They are also more common in contemporary homes than panel doors, although they work equally well in older homes.

Hollow-core doors come in both varieties, although solid doors are rarely flush style due to the difficulty of obtaining such large, single pieces of wood.

How to Fix a Hole in a Hollow Core Door

The first step to fixing your hollow core door is assembling the tools and materials you will need. All of these can be found at your local hardware store and shouldn’t cost more than $50.


  • Hammer. Any type of small to medium-sized hammer will do as you won’t be using the hook end.
  • Screwdriver. Phillips or flathead screwdrivers will do both works, although the Phillips style is better because of the smaller size of the head. A #3 Phillips is just about perfect for this job.
  • Utility Knife. An adjustable utility knife with sharp blades will make this job much easier.
  • Needle Nose Pliers. Any small tipped pliers, even a multi-tool, can be used.
  • Putty Knife. A flat-edged or chiseled edge putty knife will do both works, although depending on the hole’s size, you may need to use a bigger blade. Putty knives are available in a variety of sizes, ranging from ¾ inch all the way to 6-inch blades.
  • Popsicle Stick. A popsicle stick or tongue depressor is optimal, but any small flat piece of wood will work.
  • Sandpaper. Fine-grain sandpaper will get you a smooth surface on which to apply your matching paint.
  • Paintbrush. A flat brush will work best for this application.


  • Cardboard. Any type of thin, corrugated cardboard will work. You won’t need much, so depending on the size of the hole, leftover packaging is perfect for this purpose.
  • Low-Rise Expanding Foam. There are several brands on the market, and they all function in basically the same way.
  • Plastic Wood. When cured, these products are crack resistant and will take paint, so matching the existing color on your door will be easy.
  • Masking Tape. Any masking or painters tape will work. Don’t use electrical or duct tape as these can leave a sticky residue that will need to be cleaned later.
  • Paint. Choose a paint that matches the existing color of your door. One pint should be enough, but if you think you might use the same color on future projects (or fix more door holes), buying a larger amount doesn’t hurt.

Now that we have everything we will need to patch the hole in our hollow-core door, we can get started!

The Process of Fixing Holes in Hollow Doors

  1. In order to fix your door, it will need to be laying horizontally on a flat surface, so the first step is to take it off the hinges.
  • Starting with the bottom hinge and approaching from below, place the point of your screwdriver on the head of the pin inside the hinge and gently tap it with the hammer to push it up and out of the hinge assembly.
  • Repeat the process for the top hinge, being careful to apply upward pressure on the door so that the hinge doesn’t bend or warp due to the loss of support from the bottom hinge. If you have a helper, this is a task that can benefit from an extra set of hands.
  1. Now that the door is free from the frame, place it on a table or set of sawhorses, making sure that it is stable and fully supported.
  2. Using your utility knife, clean the edges of the hole, taking off just enough material to get a clean edge without making the hole unnecessarily larger. Adding a slight bevel to the edge of the hole can be useful in the later steps, adding more surface area for the patching material to adhere to. 
  3. Use your needle nose pliers to remove the larger bits of wood that have been removed from the damaged area of the door. Don’t worry about any small pieces falling into the interior of the door; they won’t hurt anything.
  4. Take your cardboard and cut a strip just narrower than the depth of the door. This will form a barrier that will keep the foaming material from spreading into the larger hollow space within the door. Make sure you cut your cardboard on another surface, so you don’t further damage the surface of your door.
  5. Use your needle nose pliers and screwdriver to fit the cardboard strip into the hole, creating a chamber that will contain the foam. It may take a little fiddling, but take your time.
  6. Once your cardboard is seated properly, add your low expansion foam. Be careful! A little bit of this material goes a long way, and if you add too much, it can actually expand enough to crack your door, making a small problem much bigger.
  7. While your foam begins to expand, take a bit of masking tape and use it to create a frame around the outside the hole. This will help keep the foam from sticking to undamaged areas of the door and will make the final steps a bit easier and your final product cleaner.
  8. Wait for your expanding foam to fully cure. This may take up to 4 hours.
  9. The foam will have expanded outside the hole, forming a bubble of spongy, durable material. Taking your utility knife cut off the excess material. It is actually a good idea to dig into the foam a little, creating an indentation that you will fill with your patching material.
  10. Remove the masking tape, open your plastic wood filler and apply it to the damaged areas. Spread it evenly with your popsicle stick, making sure to completely fill the gap so that your patch will be solid without air bubbles. Add a little extra filler so, during the sanding process, you can get a smooth, uniform surface that is flush with the surface of the door.
  11. Wait for the plastic wood filler to dry. This may take several hours.
  12. Use your fine-grit sandpaper and apply pressure so that you end up with a nice smooth surface on which to apply your new coat of paint.
  13. Clean the area with a damp towel to remove any detritus or dust created by the sanding process and then thoroughly dry the area with a paper towel. It is important to apply paint to a clean surface.
  14. Take your flat head paintbrush and apply the paint. One coat should be enough, but if you are feeling fancy, a second coat won’t hurt.
  15. Let the paint dry, and it’s time to hang the door back in the frame.
  16. Reversing the first two steps, place the door within the frame and slide the pin into the hinge assembly; you may or may not need the hammer to tap it into place. Repeat with the bottom hinge, and you’re done! Once again, this step may require a helper as it is important not to bend the hinges or damage the frame when hanging your door.

Optional Step: Reinforcement

On places that get a higher level of daily use or are prone to impacts–the bottom of the door, or a particular spot that comes into contact with a piece of furniture – a reinforced “wall guard” can be installed. This is a trick that can be used if you find yourself having to repair the same damaged area of your door on multiple occasions.

Wall guards can be found at any home improvement store and are usually used to protect a wall from the impact of a doorknob when opening the door. Here we are flipping the functionality and using the wall guard to protect the door.

Before hanging the door back on the hinges, peel off the adhesive strip on the back of the wall guard, place it on the area, wait 30 minutes, and you are good to go. You have a reinforced section that will never break again.

How to Fix Holes and Cracks in Wooden Doors

Another common problem with doors that homeowners encounter is cracks in solid wooden doors, occurring most commonly in exterior panel doors.

These unsightly cracks are caused by the inability of the wood panels to naturally expand and contract with changing temperatures and humidity levels. Layers of lacquer and paint hold the panels in place, and this rigidity ends up cracking the wood at weak points. If left unchecked, these hairline cracks can expand until, eventually, the door’s insulating properties are compromised.

Addressing these hairline cracks is not as difficult as many people think: this particular method was borrowed from boat builders and will leave you with a waterproof solution to cracked panels in your exterior door.

It is worth noting that, while this technique will extend the life of your door since the paint is still holding the panels in place, these cracks may continue to grow, and eventually, your door may need to be replaced altogether.


  • Utility Knife. A standard, an adjustable utility knife is an essential tool in this job.
  • Hacksaw Blade. A hacksaw blade or any semi-flexible metal blade will work in this application.
  • Flat Head Screwdriver. The width of the head isn’t of importance, as you will be using the screwdriver as a packing tool.
  • Putty Knife. Any size putty knife will work here.
  • Paper Towels. These are simply for cleaning purposes.
  • Paint Brush. A flat brush is best as you will be painting a flat surface.
  • Sandpaper. Fine grit sandpaper will help smooth your surface for paint.


  • Natural Fiber String. Any thin, cotton, or hemp twine will work; a variety with two or three strands twisted together is best. 3mm is perfect.
  • Elmer’s Glue. The classic adhesive we all know from elementary school works great here as well.
  • Plastic Wood. Plastic wood or putty will work here, as they are crack resistant and durable.
  • Paint. A small amount of paint is required for these jobs, although do your best to match the existing color unless you feel like changing things up and painting the entire door a new color.

The Process of Fixing Cracks in Solid Wood Doors

  1. The first step is to clean the edges of the crack. Using the utility knife and hacksaw blade, remove any burs or detritus that has built up in the gap. It is important to make sure that the wood of the panels is exposed.
  2. Measure out two pieces of string to a bit longer than the length of the crack. This extra length gives you something to hold onto as you proceed.
  3. Thoroughly soak the first piece of string in the Elmer’s glue, making sure that it is completely saturated. You may need to water down the glue if it is too thick and not being effectively absorbed.
  4. Use the tip of the flathead screwdriver to pack the string into the crack, starting at the top and working your way down. Be careful not to push the string all the way through, out the other side of the crack. It is also important to make sure your panels remain parallel and aren’t being twisted as you pack the string.
    Opening the door so you can easily monitor both sides is a good idea.
    If you find that your string is too thin or too thick for variations in different portions of the crack, you can gently twist or untwist the end to change the thickness and get a perfect fit.
  5. Repeat the process with the second string, once again being careful not to push the first string out the other side of the door. This can take a bit of finesse as you want the final placement to leave a small trough in the gap to allow your putty to lay flush with the panel.
  6. Let the glue harden for several hours to make sure it is fully cured.
  7. Once your glue is hardened, wipe the area with a paper towel to give the putty a clean surface to bond to.
  8. Use your putty knife to spread the material over the gap, making a smooth surface that is even across the affected area. Allow several hours for the putty to dry.
  9. Take your fine-grit sandpaper and smooth the area to prepare it for paint.
  10. Paint the area to match the rest of the door. Many people choose to paint the entire panel to achieve a more uniform and consistent look.

This process works best on painted doors as the filled areas will remain visible on stained doors. It will achieve the same results functionally, but it won’t be as pretty.

Final Thoughts

While neither of these projects require expert woodworking skills, it is always important to plan your steps before you begin. Arrange all of your tools and materials before you start any cutting, or you may find yourself running to the hardware store midway through your repair project. Remember the “Five P’s”: Proper Planning Prevents Poor Performance.

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