A caulk gun and a tube of caulk are powerful tools for the homeowner. Applying a bead of caulk is simple and satisfying, allowing you to plug gaps and cracks, prepare areas for painting, and prevent air or water leaks.

Caulk is also useful due to its versatility, with numerous varieties available to repair everything from foundation cracks to bathtub seals. It's not a catch-all, though. Some areas of the home should never be caulked, since doing so can trap moisture and cause damage.

Make sure the caulk you use is appropriate for the project you're undertaking. The Department of Energy says some caulks are flexible to allow joints to move. You should also check to see which caulk best fits the area and materials it will be applied to; some varieties are good for exterior use, while others excel at dissimilar materials.

On the exterior of the home, caulk is particularly useful in corners and edges. Elegant Painting, a company in Woodinville, Wash., says these areas are most vulnerable to water intrusion, and that an application of caulk helps keep runoff at bay. The home improvement professional Ron Hazelton says window and door frames should also be sealed; even if these have been caulked before, older caulk may have pulled away from the edges and need to be replaced.

A quick application of caulk is useful for closing off any number of cracks or holes where water or pests can enter. Donna Boyle Schwartz, writing for the home improvement professional Bob Vila, says some caulks are specifically made to close off openings in the concrete or mortar in foundations.

Weatherproof caulk is useful for roof repairs, as it will seal off gaps around flashing, skylights, and other openings. Similarly, waterproof sealant is a good way to revitalize gutters by plugging leaks.

You might be able to caulk the junctures where certain kinds of siding come together, helping to keep them in place and prevent moisture from entering your home. Elegant Painting says this shouldn't be done for cedar siding or other natural materials that are designed to expand and contract. You can also use caulk to fill in cracks, gaps, and other openings in the siding itself.

On the home's interior, caulk is useful for filling in gaps at the bottom or top of baseboards. Lee Wallender, writing for the home improvement site The Spruce, says this process makes the baseboards look better, prevents debris from accumulating in the gaps, and keeps air from leaking around them. However, you can also consider alternatives such as tightening the baseboards or replacing them with thinner, more flexible ones.

A line of caulk will cut down on drafts around window frames. You'll just want to make sure you use it to seal gaps in immobile areas. The Department of Energy says weatherstripping is a more appropriate defense against air leaks in moveable components, such as doors or sliding windows.

Caulk is a good defense against water damage when applied around bathtubs, sinks, drains, and other parts of your plumbing. Schwartz says fireproof caulk can be used to seal openings in interior framing, such as those created by wiring or plumbing, to help contain the spread of flames in case of fire.

Certain places on the exterior of the home should not be caulked, since they'll cut off openings needed for air circulation or drainage. Elegant Painting says these spaces include the gap created when trim boards sit atop the siding, any wood to metal joints, weep holes on windows, and garage door panels.

The bottom edge of siding should also be left uncaulked. Crestwood Painting, a company in Kansas City, Mo., says sealing off this edge will also prevent water runoff, trapping moisture and leading to problems such as mold or mildew.

Similarly, you should avoid caulking the bottom edges and joints of your fascia trim and soffits. Any water that doesn't get into the gutters can be trapped in these areas if they're sealed off.