When it comes to knowing how to trim a door, there are a few variables that come into play, including whether or not the door is a hollow core pre-hung door or a solid door. At ETO Doors, all our doors are solid — not all are solid wood, but even those that are fiberglass and fire or safety rated are solid (don't trim fiberglass doors yourself or as a DIY project!).

Work with Solid Woods and the Right Tools to Avoid Splintered Wood or Cracked Finish

The key when trimming a door is to get the job done without ruining the finish by scratching it, causing it to splinter, cracking the veneer or finish, and of course, to have trimmed a neat, level top or (usually) door bottom. As long as you're working with a solid wood door, issues of splintering the wood or cracking the finish are diminished, but by no means gone. To truly make these negative events virtually impossible, you will need to enlist the help of a circular saw, but before you fire it up, you will need to measure the door to decide where the trim needs to occur.

Repeat Your Cuts Using the Guide Until You Have Created a Groove for the Circular Saw

Once you have spotted your trim location, create a line using a guide and a brand new, high-quality, very sharp blade or even scalpel. Going over the line again and again with the guide securely in place, you are creating a deep groove that cuts through the finish and into the wood just enough to create a track for the circular saw to fit into. Once you have gone over the perfectly straight line with your mat knife or scalpel 10–20 times, you should be ready for the saw.

Why and How the Masking or Painter’s Tape Above and Below the Groove is so Critical

The groove you just created with your mat knife or scalpel is exactly what will keep you from splintering the wood or ruining the finish. But before setting your circular saw into the groove, you're going to place masking or painter's tape of at least six inches in width above and below the groove. This tape literally holds things in place just so during the vibration of the saw once it is started, but it also keeps the finish from getting scratched or small pieces of wood from splintering off, which would ruin the aesthetic of the door and create a need for re-sanding and refinishing.

Securing the Door to a Sturdy, Level, Straight Edge, Create Channels in the Groove

With your ultra-wide strips of tape firmly in place, you'll use two clamps — one for each side — to secure the door to a straight edge where the portion you're cutting can hang off — a classic workshop sawhorse is ideal for this. To further protect the integrity of the finish and the wood beneath, the final step before finally using your saw is to use your mat knife once more to create slightly deeper channels within the existing groove; make them 1/32” or slightly deeper, and create roughly one every three to four inches, depending on the width of the door.

Time for the Circular Saw: Use Your Groove

Finally, this door is ready for the saw. To trim well, you will turn the device on first, and with gloves and eye protection on, slowly glide into the door’s surface. Saw across the top going all the way through in a slow and focused manner, so that by the time you reach the other side of the door, the portion you’re trimming off falls to the floor. Don’t go fast or rush from one side to the other; this can render all the precautions like your tape, groove, and channels worthless if you are careless and move too fast. Once you’re done, removed the tape from your door and you have a perfectly even trim across the bottom to make way for new carpet, a new rug, or enough space to glide without skidding after you’ve re-tiled the ground surface or installed wood flooring.