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How to Caulk Window Air Leaks

Air Leaks in homes account for a sizable amount of energy loss. Many air leaks are found around the edges of windows where the window frame meets the interior and exterior wall surfaces and window trim. Here’s how to solve the problem.

Degree of Difficulty: hammer-1-5

Step One: Do a quick inspection of the inside and outside of your home. Look for cracks where the window frame touches up against anything that’s not a window. For example, your window may contact brick, stone, wood or vinyl siding and plaster or drywall. The cracks may be as small as the thickness of a piece of paper or as wide as the diameter of a pencil. On the inside of your home look at both sides of where any wood trim around the window contacts the window frame or the wall surface.

Step Two: Purchase several tubes of siliconized acrylic caulk. Consider using caulk that dries clear so you don’t have to do any painting. Avoid using pure silicone caulk. It is very hard to expertly install silicone caulk. You want caulk that is water washable and easy to clean up.

Step Three: Purchase a high-quality caulk gun and a good grout sponge. High-quality caulk guns usually are priced around $20 and sport a higher thrust ratio of about 18:1. This means you have to squeeze the handle more times to get the caulk to flow from the tube. Although this may seem like more work, you get far greater control than the inexpensive caulk guns. Grout sponges have nice rounded edges, not sharp corners.

Step Four: Only caulk the exterior cracks at your home if the air temperature is above 40F and will stay there for at least twelve hours. Read the label of the caulk to see if the instructions say differently. You want the caulk to cure before it freezes.

Step Five: Trim the tip of the caulk tube slowly taking off just small amounts of the plastic. You want the hole at the tip of the tube to be no wider than one-eighth inch. Wide holes allow too much caulk to flow creating a huge mess. You can always trim more off the tube tip. Start with a small hole to see how it works.

Step Six: Wipe the crack to be caulked with soapy water to clean the area on each side of the crack. Dry it immediately with an old towel. You don’t want the area around the crack to be dirty so dirt gets into the fresh caulk as you smooth it. Do all the cleaning around all cracks before you start to caulk.

Step Seven: Apply the caulk to just two linear feet of crack. Glide the caulk nozzle over the crack at a speed that allows just a small amount of excess caulk rise above the actual crack. Do NOT apply too much caulk.

Step Eight: Using your finger, glide it across the crack so the caulk is pushed into the crack. If large amounts of excess caulk build up on your finger, lift your finger from the crack and deposit this excess caulk onto the crack that’s yet to be caulked. Finish tooling the caulk with your finger until all the caulk has been smoothed.

Step Nine: Dip the grout sponge in warm clean and clear water. Squeeze out any excess water. No water should be dripping from the sponge. Slide the sponge with moderate pressure over the crack making sure you don’t gouge out fresh caulk from the crack. You’re trying to use the sponge to clean off any caulk from the edges of the crack where your finger smeared it. Rinse the sponge frequently and make repeated passes over the crack until all smeared caulk is removed from either side of the crack.

Step Ten: Change sponge water frequently so the window, trim and wall surfaces do not get fouled with caulk.

Summary: If you’ve not caulked before, I urge you to practice first. Locate other cracks around your home in out-of-the-way areas or start with the windows you see least. It won’t take much practice to get professional results.

Column: HT001




10 Responses to How to Caulk Window Air Leaks

  1. Enjoyed recent email on caulking windows; I knew a lot of it, but it was a good review. What I need now is a good article on restoring or replacing the grout on old NE multipaned windows (6 over 6 and even some 12 over 12's) other than installing new modern windows. I'm looking for new methods or tools and techniques. As you know, this process is one of the most laborsome and frustrating for any DIYer who owns an old colonial in NE; it takes forever!

  2. Recently, I was trying to unplug a bathroom sink using every possible snake to unclog the drain. After hours of no success, I placed a wet vacuum to the drain and in a few seconds heard and felt two distinct "THUMPS" Both were clumps of caulk that had collected hair and soap and just refused to be pushed down the drain. That was lucky. Had it repositioned further down, I'd be looking at a bigger mess. Moral of the story: DON'T even think of rinsing off your hands in a sink after getting caulk on your hands.

  3. Tim, sealant installation was one of the trades I became proficient in during my time on the wall. Tip #1: keep your finger tip out of the caulk. I realize you are talking to beginners but listen up, a plastic spoon will be readily available and can be shaved to the approximate dimension of the joint. Because it has a rounded shape it will be a user friendly tool. A steel spoon would be better and glazing spatulas are best. Tip # 2: 1/4-inch is the minimum wide dimension of a sealant joint. (Sealant joints manager movement and water/air. Caulk joints are for aesthetics.) The material you suggested is flexible enough to do the job. 1/8-inch is not wide enough to grab onto both sides of a crack with enough holding power to be meaningful.

    Great topic keep up the good work.

    Mike Collins

  4. Tim,
    Thanks for the "better" way of applying caulk. One thing that was missing was the direction of the caulking gun; I find it very effective to slowly push the gun forward over the bead of caulking as it leaves the nozzle so that the caulk is forced into the crack ahead of the gun and the nozzle can do part of the job that you have your finger doing. Drawing the gun away from the bead of caulking just invites a mess

  5. As a proud, life long member of Caulkers Union 66, I find your article to be disingenuous and insulting. To imply that mere riffraff plebeians can master the art of proper caulking after reading 10 steps and a couple of minutes of practice on Fido's dog house is insulting to my profession and skill. You, my good sir, are a scoundrel of the most notorious kind. Good day to you.


  6. It seems impossible to caulk a window air leak on the outside if the vinyl window frame is lapping over the vinyl siding. I can't "see" the crack from the outside. Occasionally, on the inside I will hear the whistling wind entering the room around the edge of the window frame and the drywall opening. So, my only remedy would be to caulk the inside of the window(s). Does that sound logical ?

    Many thanks.

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