How to Caulk Interior Window Trim

How to Caulk Interior Window Trim Like a Pro

Window trim is a key part of any room, but it can be tough to keep it looking nice and caulked.

Preparation is the most important part of any project, and it’s especially true when learning how to caulk interior window trim.

With our easy how-to guide, you’ll be able to caulk a window with confidence and ease, and you’ll be able to keep your trim looking nice year-round. So without further ado, let’s get started!

Materials Needed

  • Caulk Gun
  • Acrylic latex caulk
  • Putty Knife or Spackle Knife
  • Clean cloths such as rags or paper towels
  • WD40 for cleaning out old caulk
  • Caulking gun (optional)

Steps on How to Caulk Interior Window Trim

caulk interior window trim

The Surface Should be Cleaned

Wipe down the surface of both sides of the window trim with a clean rag to remove any debris that might have gotten stuck under your old caulk, like dust and dirt particles.

Spray WD40 over both surfaces (the side you want to install new caulk AND the area where your old caulk was). If you prefer not to use WD40, another lubricant can be an acceptable substitute.

Use a Removal Tool

Use a caulk removal tool like a putty knife or spackle knife to gently remove the old caulk from each side of your interior window trim. Whether it’s an old or new window, you can still use the same trick.

Once both sides of the interior window trim are free of the old caulk, wipe down each side again with a clean rag or paper towel before moving on to installing the new caulk.

Inspect Your Window Trim

Before you begin, take a look at your window frame and find out if any pieces have been broken off from previous moves or accidents. It is possible to make repairs yourself with wood putty or caulk provided that you can still see the end of the piece that needs to be filled.

Apply the Caulk

Using a caulk gun, apply a generous bead of the acrylic latex caulk or silicone caulk on top of both sides of your interior window trim

Use your finger to smooth out and spread the caulk around so that it is as even as possible. Try to work quickly as some cauk will set within seconds.

Remove Excess

With a putty knife or spackle knife, scrape off any excess caulk from either side of your window trim. Make sure all edges are straight, and there’s no excess caulk along the outer or inner edge. If you do not correct it before it dries, the caulk has a tendency to shrink and may crack.


After your new caulk has dried for about 15 minutes, re-inspect your window trim from both inside and outside your home. Do you see any spots where excess caulk was not scraped away? If so, remove them right away before they dry. You can use the removal tool again if necessary, or you can use a towel or rag with water to wipe away the excess caulk.

Finishing Touches

Your window trim should now have a clean, smooth finish so that it looks great from inside and outside your home. If you’re happy with the results, use some caulk to seal up any other gaps or holes that were not taken care of during this project.

If you completed these steps correctly, then congratulations! However, you should keep in mind some important factors outlined below.

Important Factors to Keep in Mind

Professional Caulking Gun

Using a Quality Caulk Gun

A good caulk gun will allow you to control the speed at which your caulk comes out, meaning that it is easier for you to apply a nice even bead of caulk every single time. If your caulk gun does not work very well or if it gets clogged up easily, consider purchasing a better model in the future.

Window Trim Maintenance

Keeping your window trim looking its best requires periodic maintenance and touchups when necessary. You should inspect all of your interior window trim yearlies or once every season to check for cracks in the caulking.

Choosing the Right Caulk

In order to have a successful window caulking project, you need to use the right type of caulk for your window trim. In most cases, it is best to buy an acrylic latex caulk that has good mold and mildew resistance. You can also use this sealant for your exterior window or door frame.

Overlapping Old Caulk isn’t a Wise Idea

When your old caulk starts to look worn or it isn’t doing a very good job of keeping out water, mold, and mildew particles, you need to replace it. Do not overlap the old caulk because this can cause cracking in your new caulk joints.

Cut The Caulk Tube Tip Just Enough to Seal It

When using your caulk gun, make sure that you do not cut the end of the caulk tube tip too much. This is because excess caulk can ooze out, and it may end up ruining your project.

Ride the Smooth Way

When you are running out of caulk, do not pull away from the tube. Press your trigger or squeeze handle slowly and try to ride the smooth way all the way down your window trim. If you remove the pressure on the caulk gun before it is finished, then you may end up with unsightly bubbles in your caulking windows joints.


Do you caulk interior windows before or after painting?

It is always best to interior caulk your window trim before painting since it is much easier. If you do not caulk before painting, then the results may be less than satisfactory, with many gaps and cracks that can lead to air leakage problems in your home.

Do I need a special tool to apply caulk?

In most cases, no. You can use a common caulking gun with regular spackle knives or putty knives if necessary. However, there are certain jobs that may call for a special caulking gun, but it all depends on what type of caulk you will be using.

How long does caulk last?

Caulk should last a few years before it starts to dry out and crack. This is why regular maintenance is so important. If you do not maintain your interior window sill then the caulk joints may start to fail after as little as six months. In most cases, it’s best to replace your caulk once every 3-5 years if possible.

Can you caulk and paint on the same day?

It is possible to caulk and paint on the same day, especially if you use a paintable acrylic latex caulk or polyurethane caulk. However, it may be best to wait for your new caulk to dry before interior or exterior painting.

How do you remove old caulk from window trim?

You can scrape off old caulk with a sharp metal putty knife or razor blade (with care) in most cases. If this does not work, then try using a heat gun or hairdryer. A little bit of denatured alcohol should be enough to get the remaining residue off the old window trim completely.

Last Words

Now that you know how to caulk interior window trim, have fun practicing this new skill in some other parts of your home.

Once you have mastered it, you’ll no longer have to worry about drafty windows and unsightly gaps in your window trim. Good luck!

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