What’s the Best Type of Caulk for Sealing the Outside of Your Windows?

Ginny Bartolone
Written by Ginny Bartolone
Updated November 23, 2021
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Properly sealed seams around the exterior of your home's windows act as a fortress, which protects your home against cold drafts, moisture, and even pests. When the time comes to replace the caulk around your window frames, choosing the right variety of caulk is a crucial step. If you're feeling lost in the caulk aisle of the hardware store, take a look at this guide to help you make a decision.


What to Look For in Exterior Window Caulk

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Shopping for caulk may sound straightforward, but you'll find quite the range of materials and uses on the market. Since all window designs and home siding are slightly different, there isn’t a one-size-fits-all option for sealing the outside of windows. 

However, you can start by asking these questions:

  • What type of material will the caulk need to adhere to on the outside of my house?

  • Will the caulk regularly come in contact with moisture and sunlight?

  • How often will the temperature change around the caulk?

  • How large is the space that I need to fill?

  • Do I want to paint over the caulk to match my window frame?

Each answer points to a different caulk material. For example, exposure to temperature changes—typical for the exterior of your home—requires a caulk that can easily expand and shrink without cracking. Or, if you want to paint over your caulk, you'll need to opt for a variety made with latex. Even the size of the crack around your window can determine the right option.

A 10-ounce tube of caulk typically costs anywhere between $3 and $10, so opting for a higher-quality or more specific caulk is not going to sway your project cost too far. 

1. Siliconized Latex Caulk: Best Overall

The construction industry combines the best of both worlds with siliconized latex caulk, also referred to as silicone latex or "latex with added silicone." While these combos will cost a few more dollars than a bottle of plain latex, they offer the easy application and paintability of latex, with the stretch and adhesive powers of silicone.

Siliconized caulk is also tough against moisture, sun, and temperature changes. You will often see it used on bathtubs and showers due to its strength against water, heat, and mildew.

As always, there's a minor drawback. The presence of silicone means the caulk will have a very powerful odor. Its potency isn't as big of an issue if you're working outside, but keep this in mind if you're working in an enclosed or partially enclosed area. Always ensure there is plenty of ventilation in your workspace and that you wear a protective mask.

2. Silicone Caulk: Strongest Against the Elements

Are you looking for a strong and stable caulk for the exterior of your windows? Silicone-based caulk is a popular option, especially for outside work. Not only can it stand up against moisture, but it's tough against mildew as well. That’s why you're more likely to find silicone caulks in bathroom showers and tubs

Silicone caulk seals your windows from outside drafts, moisture, and insects while remaining flexible to changing weather outside. For one, silicone naturally stretches and elongates due to its inherent elasticity. So, as the temperature heats up and cools down outside, you won't have to worry about the bead chipping or breaking.

When purchasing silicone caulk, check the label to ensure it adheres to your window seam material. For example, acid-cure silicone caulk works best on metal siding, whereas neutral cure may be better on wooden siding or sills. Overall, silicone caulks are best for tricky materials, such as metal, marble, and glass, especially against the outdoor elements.

Keep in mind that you cannot paint on top of silicone caulk—the paint will simply bead up and not adhere to its surface. It will also darken during the curing process, so it's often best when used in a spot that blends in with the house.

3. Polyurethane Caulk: Best for Pest Protection

Do you have a large opening between your window frames? Your best bet is to seal the gap with a highly expandable foam made of polyurethane caulk. Polyurethane caulk expands to fit the small openings along the seam of your window and adheres to nearly all common frame materials, including wood, marble, and ceramic. This tight seal is ideal for keeping pests out since there's simply no room for them to get in. You can even purchase a foam that specifically advertises its toughness against pests, like ants.

Polyurethane caulk can be a bit harder to use since it's not water-soluble—as in, you can't clean it up with water—so be careful not to let it splash beyond your window seal. If it's in direct sunlight, you'll need to add a layer of paint on top of the polyurethane caulk, as it's typically not UV protected.

4. Butyl Rubber Caulk: Best for Concrete

If your window frames come up against water-prone areas, especially on materials like concrete, butyl rubber is a good option. The material is highly resistant to moisture, even when adhering to hard materials commonly found around your home. This variety is typically used in commercial buildings made of concrete, but it can work on gutters and flashing options. You may also want to consider butyl rubber if you have an area to fill that’s larger than a quarter of an inch due to its highly expandable qualities.

5. Latex Caulk: Honorable Mention for Indoor Windows

Latex caulk typically only works on the inside of your home since it doesn't hold up well against the elements, but some acrylic mixes can stand in for quick outdoor fixes. Overall, only use latex caulk in areas that are not prone to extreme moisture.

However, sealing the inside of a window requires a caulk with lower VOCs and a nice appearance. Volatile organic compounds, or VOCs, emit potentially harmful chemicals and can be found in many household construction and cleaning products. But overall, it smells good, and it looks good. These qualities make latex and latex acrylic latex caulks a great option for inside use.

You will certainly find sturdier indoor caulks on this list, but since latex is so easy to clean and manipulate, it's a go-to choice for home DIYers who are learning how to caulk windows and patch small areas. Latex caulk is also paintable, so you can paint the bead to match the rest of your window once it dries. 

Caring for your windows over time is one of the best ways to control fluctuating temperatures and keep out pesty visitors. But take your time choosing the right type of caulk for the outside of your windows to ensure a study fix.

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