How To Fill Gap Between Door Trim And Wall; A Simple DIY Tutorial

How To Fill Gap Between Door Trim And Wall

There are several reasons for the gap between your door trim and the wall. It could be due to poor installation, weather, expansion and contraction, missing nails, or even shrunken caulk. The truth is, no matter how well the door trim was installed, it will eventually shift from the wall, leaving a gap. 

Door trim gaps are not only unattractive but can also cause infiltration; that is, the small space can become a passage for air from and into your home. And this can force your heating and cooling system to work harder, resulting in higher electricity consumption.

No matter the cause of the gap between your door trim and wall, you can fill it. All you need is a painter’s caulk, a few home improvement tools, and the simple steps discussed in this tutorial. And you are set to seal up the ugly space around your door and restore beauty to your interior space.

How to Fill Gap Between Door Trim and Wall With Just Caulk

If the gap between your door trim and the wall is ¼-inch or less, you can fill it with caulk alone. However, there are various types of caulk available, and you should know which one is best for filling the space on your door casing. 

I recommend that you use acrylic latex caulk. This caulk is inexpensive, quick-drying, and paintable. This is why it’s also known as “painter’s caulk.” However, if you have “paintable” silicone caulk, you can use it. Silicone caulk is also a strong adhesive glue that can be used to seal any gap on any home surface.

Summary – The best way to fill the gap between your door trim and the wall is to use an acrylic latex caulk. Simply apply caulk to the gap with a caulking gun, let it dry, and then paint over it to match the wall and the trim. But when dealing with a large gap, ¼-inch or wider, it is best to fill it with foam first before applying the caulk. 

Tools needed to repair a door trim gap include;

  • Putty knife
  • Caulking gun
  • Utility knife
  • Bowl of water
  • Paint
  • Paintbrush

Once you have your tools, follow these simple steps to fill the gap on your door trim and wall:

Identify the cause of the gap between door trim and wall

1. Identify the cause of the gap

The first step is to identify the source of the gap. Is it due to faulty installation, a missing nail, or expansion and contraction?

  • If the gap results from improper installation, you may need to remove the door trim and reinstall it properly.
  • If any nails are missing, simply drive new nails in with your hammer to secure the trim.
  • Expansion and contraction cause the majority of door trim gaps. So, if that’s the case with your door trim gap, use the steps below to repair it.

2.     Measure the Gap

The next thing you want to do is find the exact gap between the trim and the wall. This helps to determine the best filler material to use. 

You can easily measure the size of the gap by merely looking at or using a Digital Vernier Caliper for an accurate measurement.

  • Insert the small jaw of the caliper in the inner space
  • Use the adjustment buttons on the caliper to get an accurate measurement of the depth and width of the gap.
  • Once you have ascertained that the space is small enough to fill with just a caulk, proceed to the next step.

3.     Clean the Gap

You have to prepare the trim and wall surfaces for caulking. This entails scraping old paint and caulk off. And the purpose is to ensure that the new caulking adheres firmly and lasts longer on the surface.

  • Using a putty knife, scrape off dried caulk and paint from the wall and door trim.
  • Remove any remaining debris with a brush or vacuum cleaner.
  • If there is oil dirt on the surface, clean it with a degreaser or rubbing alcohol.
  • Allow the surface to dry completely before applying caulk.

4.     Apply Caulk

Apply Caulk to gap between door trim and wall

It’s now time to seal the tiny gap on the side of your door casing. Caulks dry quickly, so only cut open the caulk tube when you’re ready to apply it.

  • Using a utility knife, cut the tip of the caulk tube at a 45-degree angle. Because you’re filling a small gap, don’t cut the tube too wide open; it should be about ¼-inch wide.
  • After cutting, use the caulk gun’s pin to puncture the inner seal of the tube.
  • Then, insert the caulk gun tube and press the rod against it.
  • Squeeze the trigger to release the caulk and apply it along the gap’s edge. 

5.     Smoothen the Caulk Edge

When you’re finished applying the caulk across the joint, smooth it out and wipe away any excess caulk before it dries.

  • Dip your finger into the water in the bowl, and run it along the caulk line to force the caulk into the gaps and smooth the surface.
  • Periodically rinse your finger in a bowl of water to prevent caulk buildup.
  • If any gap remains, fill it with more caulk and smooth it with a wet finger.
  • Wipe away any excess caulk from the trim and the wall before it dries.
  • Allow the caulk to dry completely for the amount of time specified on the package.

6.     Finish Up Caulking and Apply Paint

The caulk may shrink slightly as it dries, leaving small gaps in the caulk line.

Fill a Large Gap between Door Trim and wall

How Do You Fill a Large Gap on Your Door Trim?

If the gap between the door trim and the wall is wider than ¼-inch and deeper than ½-inch, then you must fill it first before applying the caulk. This provides more support for the trim, reduces the amount of caulk required to fill the space, and prevents the caulk from cracking over time.

There are several materials that can be used to fill large gaps on your door trims, but these are my favorites;

Backer Rods

The backer rod is a thin foam rod used to fill gaps and reduce the amount of caulk required to fill them. Even when exposed to moisture, the rod will not warp, rot, or crack, allowing the caulk to last longer.

Here’s how to fit a backer rod into a door trim gap:

  • Measure the distance between the door trim and the wall using your digital caliper.
  • Buy a backer rod that is the same thickness as the gap. Amazon sells baker rods in a variety of sizes, including 1/2-inch, 3/8-inch, and 5/8-inch.
  • However, if you have a rod that is smaller than the gap width, you can still use it. Simply fold the rod in half and twist the two halves together to make a thicker rod.


Another option is to insert a few shims into the gap before caulking. Shims are available in a variety of sizes and are made of wood or plastic. They are ideal for adding extra support to the trim and preventing caulk from cracking.

How to install shims in a door trim gap;

  • Measure the gap and purchase the right size shim.
  • Cut the shim into smaller pieces and insert them into the gaps to fill a significant portion of space.
  • Tap shims with a rubber mallet to fit snugly into the gap.
  • Then follow the steps outlined earlier in this guide to apply the caulk.


You can also fill the large gap on your door trim with cushion foam. This is the easiest and cheapest material you can find around the house.

How to Install Foam in Door Trim Gaps

  • With scissors, cut the foam into tiny pieces and stuff it into the gap.
  • Using a putty knife, push the foam into the gap until it is flush with the trim.
  • Once the foam has filled the entire gap, follow the steps discussed in the previous section to apply the caulk and paint.

Frequently Asked Questions

Can I Fill the Gap on my Door Trim with Silicone Caulk?

Yes, you can use silicone caulk on your door trim as well. Silicone caulks are strong adhesives and sealants that can be used on a variety of household surfaces; they are more moisture-resistant than latex caulk. However, a pure silicone product is oil-based. And while it makes a good seal, the paint will not adhere to oil-based silicone caulk. So, look for silicone caulk that is labeled “paintable.”

Should I use Caulk or Wood Filler?

Filling a door trim gap with wood filler is not a good idea. A wood filler is only effective for filling wood and nail gaps. Only use silicone or acrylic latex caulk to fill the gap on your door trim.

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