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Caulking is easy and cost-effective

Use caulk to permanently seal air leaks in spots such as the cracks and gaps between exterior window and door frames and your home’s siding. Generally speaking, you can seal openings up to 1/4 inch with caulk alone. For larger gaps, you’ll need to add a backing material before caulking or use a spray foam sealant instead.

Older wood windows may have glass panes that are held in place with putty and glazing points. If the putty is cracked or missing, it is a likely air leakage location and must be re-puttied. (Broken panes should be replaced.) Although caulking may be used to repair/replace window putty, it may be difficult to apply neatly and make future repairs a challenge.

When shopping for caulk, you may be overwhelmed by the choices, so be sure to read the labels on the tubes and choose the caulk that will work best with the materials you’re sealing. Most types of caulk are sold in tubes that fit a caulking gun. In addition, some caulks come in aerosol cans; they’re a good choice for filling gaps up to 1/2 inch. If your budget allows, spend a little more for a higher-quality caulk. The benefit will be a longer-lasting seal; inexpensive caulks may last only a few years, while premium caulks will last much longer. Also note that some caulks are for indoor use only, and that some are paintable—while others are not.

Before caulking, note the following points:

  • Remove old caulk and loose materials completely.
  • Make sure all surfaces are dry and free of dirt, grease, or oil; wipe with rubbing alcohol to clean.
  • Do not apply when below 50 degrees F or when rain is possible before curing is complete.
  • Tape the edges of the crack to keep caulking off adjoining surfaces.

Follow these tips to get a neat, uniform bead of caulking:

  • Cut the nozzle at a 45 degree angle at the point where the diameter is equal to the size of bead you need—near the end for a small bead, farther up for a wider one.
  • While applying constant pressure on the trigger, hold the gun at a 45 degree angle and move it slowly along the joint you are sealing.
  • Make sure you have enough caulk in the joint to seal both edges and allow for any shrinkage.
  • Smooth the caulk with a finger (use disposable gloves) or a plastic spoon for materials such as silicone or oil-based caulks.

Once you have applied the caulk, it takes time for it to dry, or cure. Curing time is described two ways. The tack-free time tells you how quickly the fresh caulk’s outer surface will dry—or skin over. The total cure time indicates the time required for the caulk to become completely stable—or reach the point where no further drying or shrinking will occur.

Most caulks pose no known health hazards after they’re fully cured. However, some high-performance caulking compounds contain irritating or potentially toxic ingredients, and you should apply them only when there is adequate ventilation; carefully read the manufacturer’s instructions and take the appropriate precautions. In addition, make sure pets and people do not come into contact with fresh caulk.

Use expanding foam for large gaps

Expanding foam is ideal for filling larger cracks that caulks can’t handle. It comes in aerosol cans and takes a short time to cure. The foam is very sticky and attaches itself quickly to whatever it touches, so be prepared to pick up any messes fast.

  • You also can use foam instead of caulk for sealing in your attic; low expansion foam will stick better to dusty and dirty surfaces than caulk (see section on "Air Leaks").
  • Low-expansion spray foam should also be used to seal the space between framing and jambs in windows and doors; standard expanding foam can cause jambs to warp and affect operation of the window or door.
  • When you’re working in a large area such as your attic, it may be inconvenient to carry and keep track of several cans of expanding foam. Instead, consider renting a contractor’s foam gun, which has a long nozzle and can help you get into tough-to-reach spaces.

Try these materials for special jobs

In addition to the types of caulk and spray foam sealant described above, you may need to use fillers to plug extra-wide gaps. Fillers come in a wide variety of materials—cotton, fiberglass, foam, and sponge rubber—and you can find them in the caulking department of your local hardware store or home center. However, these fillers are not designed for exposure to the elements; you’ll need to caulk or seal over them.

  • To close gaps too wide for foam, use foil-faced bubble wrap. For really large holes, cut sections of rigid foam insulation to fit and glue into place with expanding foam—before covering with wood or another appropriate building material.
  • For winter, use rope caulk to seal windows and other spots that you’ll want to be able to open during the spring. Rope caulk is a gray, putty-like material that comes in long strips or rolls. It’s easy to install and remains flexible, and you can just pull it off when the weather turns warm. Note that rope caulk will not last longer than a year, and oil-based rope caulk may stain painted areas.


Steps to caulking

Laying a consistent bead of caulking can take some practice. Follow these steps to provide a good seal:

  • Insert tube into gun.
  • Cut tip at 45 degree angle at desired thickness; use wire/nail to break seal at base of spout.
  • Squeeze trigger while moving tip steadily along joint to be filled.
  • Smooth bead with tool or gloved finger, making sure both edges are covered.