How to Caulk Windows Inside: 4 Easy Steps


Caulking is a very important process when you’re installing your windows. It minimizes slits and leaks, ensuring that no air passes through the joints. This is especially important for energy saving.

The process of applying new caulk around your windows from inside the home is simple:

  • Find all air leaks and mark them
  • Choose the right caulking compound
  • Remove the old sealant and apply a new one
  • Smoothen it and get rid of all excess 

1. Finding Air Leaks

Since you’ll be applying caulk directly on the spots that are letting air through, the first thing to do is locate those spots. 

Keep in mind that some construction companies caulk windows as soon as they install them. However, it could be that it’s been a long time since they were installed, and caulks or gaps may have formed.

The most common causes behind leaks are wear and tear, aging, and effects of the elements. This applies to both the caulk and the window.

You’re going to have to detect air leaks for each window individually. The window corners and the frame are the most likely spots for a leak to occur. 

Wear and tear signs on the caulk are the most common sign of leaks. Cracks and a rattling window frame are other telltales.

Because not all gaps are visible at first glance, you should employ a variety of methods to detect them: 

  • The light test: Check if light is passing through the seals with a flashlight in the evening. You can also darken your home during the day and check for sunlight.
  • Candle test: Light up a candle and move it slowly around the window frame. You’ll notice a more rapid movement of the flame in points where air seeps through.
  • Use a thermal camera: This is a more advanced, expensive, but also the most accurate method. Since it’s unlikely you have a thermal camera of your own, you can usually rent one in hardware stores.

2. Choosing The Right Caulk

There are caulk cartridges that need caulking guns to apply, and there are self-applying caulk cartridges. This doesn’t make a major difference, but caulking guns provide more stability (you’ll draw straighter lines).

The table below shows you what sealants you can use for windows, from best to worst:

Type of caulkUsageCost
Butyl rubberGlass, wood, plastic, metal, and concreteNot too expensive
Water-based sealantWindows and doors in new constructionExpensive
PolyurethaneLarge cracks (it expands after applying), mostly used with brick, cement, wood, and PVCModerate
SiliconeMetal, wood, stone, brick, bathroom tileExpensive
LatexJoints around tileModerate

It’s best to use butyl rubber when caulking windows because this sealant works with different materials, including PVC and marble. 

Gauging how much caulk you need is another problem. According to the Department of Energy, half a container is usually enough for one window. Keep this in mind when you’re buying.

3. Caulking The Window

Remove the old caulk and clean the window frame thoroughly before starting. In this way, you can reveal cracks that you’ve missed during inspection.

This is the most grueling part of the job – it can take hours to get rid of all the caulk from all the windows. However, this step is essential since new sealant may not adhere to the old one.

Because caulk is a partly wet material that’s going to dry in the air, it’s best to apply it in spring or summer. It will dry in temperatures above 45°F.

When you start caulking, hold the end of the cartridge at a 45-degree angle. Caulk will move into the crack immediately, but you have to move the cartridge slowly.

Try to move consistently with no stops and press the tip of the tube as close to the material as possible. Don’t hold the caulk cartridge in the air.

Even though some caulk materials expand after application, they’re vulnerable while applying. It’s possible that the caulk will shrink or move out of the way if applied incorrectly.

If this happens, wait until it dries and becomes stiff, remove it, and repeat the caulking process.

4. Smoothing and Removing Excess Caulk

Don’t move on to the next window right after applying caulk. You should instead smooth out the caulk you just applied and remove the excess.

Why should you do it immediately after? Because it’s going to harden very quickly, especially if it’s very hot outside, and you’ll end up with too much caulk.

Use a clean stick or a finger (provided you’re wearing gloves) to run over the caulk. This will leave you with a smooth layer.

Remove the excess with a rag or paper towels.

Once you’re done with all the removal, you can let the caulk dry. It will usually take about 24 hours.

Don’t Caulk Weep Holes

Even though you should definitely caulk your windows, there are a few things you want to avoid.

One of these things is the so-called “weep holes”. Their purpose is to air moisture out, and you can find them in almost all types of windows.

The only windows that don’t use weep holes are windows with a special sill. If your windows have weep holes, don’t cover them with caulk as you’ll ruin your window.

Why Is Caulking Important?

It’s important to caulk both the exterior and the interior before painting your home for several reasons. 

When you caulk your windows, you’re also preventing rainwater from entering your home. For everyone afraid of creepy crawlers, know that you’re also preventing bugs from calling your home their own.

You’re also keeping moisture out, as well as wind, cold, and heat.

Lower the Heating Bill

This benefit is the most important one. Keeping your home cold during the summer and hot during the winter can be difficult.

However, this isn’t just a question of comfort, but a question of financial responsibility. 

According to the Consumer Federation of America, caulking cracks is a great way to save money.

Your home becomes more energy efficient as soon as you caulk your windows. An energy-efficient home is also a cheaper one.

Even though the upfront cost may be greater (you have to pay for materials and labor if you’re not caulking yourself), you’ll save on heating!

During the summer, you’ll be losing less cool air, and in the winter, you can trap warmth inside because you caulked your windows. 

Waterproof Your Home

If there are any cracks near your windows, you’ll likely leak rainwater and melt snow through them.

This also means that it may develop mold on that same spot, which is unhealthy on top of being dirty.

Caulk Alternatives

Some people are afraid of the possible toxic effects of caulk compounds and want to explore other possibilities. 

If you don’t want to use caulk, there are a few alternatives that you can try.

Keep in mind that modern adhesive compounds are tested before being mass-produced. Additionally, most professionals agree that nothing can substitute modern caulk compounds.

Spray Foam

Even though spray foam technically is a kind of caulk, the biggest difference is in the expansion. After applying it, spray foam will expand greatly as it stiffens.

This, obviously, won’t look good, but if you’re isolating a garage window, for example, nobody will notice. 

In fact, construction companies primarily use spray foam in attics instead of standard caulk compounds.

Sealant Tape

This is a great temporary solution to fix cracks, usually used with ductwork. However,  you should only apply it on cracks that you plan on caulking in a while. Sealant tape is going to let up a lot faster than other sealants.

To Summarize

Caulking your windows is the best way to finish insulation and ensure that no air leaks occur. These leaks can cool your house down in the winter and let cold air out in the summer.

Caulked windows also look smoother and stop rainwater and melted snow from getting in.

To caulk your windows, firstly find all the leaks. It’s not likely that every single window in your home has a leak, so mark the ones that do.

Remove the old caulk and clean the working area before applying the new sealant. Use half a cartridge of caulk per window, smoothen it and remove the excess.

Let it dry for at least 24 hours and you’re done!

Tom Lovric

Tom is a writer with plenty of hands-on home maintenance experience, as well as a passion for energy efficient homes. If he's not writing, you can find him running, hiking, or playing football (but you're more likely to find him watching it on TV)!

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