Exterior Caulking: Where, How, and Which Type
FriendsWithTools.io earns a commission from qualifying purchases made through links on this page, at no additional cost to you. We do not test these tools ourselves — all claims are sourced from manufacturer specifications, retailer listings, and aggregated user reviews, each linked inline. Prices and ratings were verified on May 2026 and may have changed.
Exterior caulking is the cheapest weatherproofing you can do. A few tubes of caulk and an afternoon of work can cut drafts, prevent water damage, and save noticeable money on heating and cooling. The trick is knowing where to caulk, which product to use, and how to apply it so it actually lasts more than a season or two.
Types of Exterior Caulk
Silicone is the most durable exterior caulk. It stays flexible for 20 or more years, handles extreme temperatures from well below freezing to above 400 degrees Fahrenheit, and does not shrink over time. GE Silicone II ($6 to $9 per tube) and DAP Silicone Ultra ($7 to $10) are the most widely available options. The downside: silicone cannot be painted and it does not adhere well to wood. Use silicone for glass-to-metal joints, flashing seams, and anywhere you do not need paint coverage.
Polyurethane caulk is the best all-around choice for most exterior joints. It is paintable, bonds strongly to wood, masonry, metal, and vinyl, and lasts 15 to 25 years according to manufacturer specs. Loctite PL S40 ($7 to $12) and Sashco Big Stretch ($8 to $11) are popular polyurethane and modified-polyurethane options. Polyurethane is harder to tool than silicone and cleans up with mineral spirits rather than water, so it is messier to work with.
Siliconized acrylic latex is the easiest to apply and clean up. It tools smoothly, accepts paint readily, and washes off hands and tools with water. DAP Alex Plus ($4 to $6) is the standard in this category. However, it only lasts 5 to 10 years outdoors and is not suitable for joints with significant movement. Use it for low-stress joints like where trim meets siding on a sheltered wall, not for high-exposure or high-movement joints.
For joints wider than a quarter inch, consider a textured or elastomeric caulk designed for large gaps. Sashco Big Stretch handles joints up to 2 inches wide without a backer rod. OSI Quad ($8 to $12) is another option that bonds to virtually any building material and stays flexible in cold weather. Read the tube label for the maximum joint width before applying.
Where to Caulk Outside Your Home
Caulk every joint where two different materials meet on the exterior: siding to trim, trim to window frames, trim to door frames, where the siding meets the foundation, around exterior light fixtures, and where pipes or wires penetrate the wall. These joints open and close with temperature changes, and gaps as small as an eighth of an inch let in moisture and air.
Around windows, seal the joint between the window frame (or brick mold) and the siding or trim. This is one of the most common air leakage points in a home. According to the Department of Energy, air leakage around windows and doors can account for 25 to 30 percent of heating and cooling energy use. A tube of caulk per window costs a few dollars and takes 10 minutes.
Do not caulk the bottom edge of siding courses. Water that gets behind the siding needs a path to drain out, and sealing the bottom edge traps moisture against the sheathing. Do not caulk weep holes on brick veneer walls. Do not caulk where flashing should be doing the work. Caulk is a sealant, not a substitute for proper flashing. If a joint is larger than a quarter inch, use backer rod to fill the gap before caulking. Backer rod ($3 to $5 for a 20-foot roll) is a closed-cell foam rope that fills the gap depth so the caulk only needs to bridge the surface.
Walk the entire exterior of your house with a tube of caulk and a notepad. Mark every joint that shows daylight, cracked old caulk, or visible gaps. Start at the roof line and work down. Pay special attention to the south and west faces of the house, which take the most sun and weather exposure.
Joint Preparation
Old caulk has to come out before new caulk goes in. A 5-in-1 painter's tool or a dedicated caulk removal tool like the Husky 3-in-1 ($5 to $8) scrapes out the bulk. A utility knife cuts through stubborn sections. For silicone caulk removal, a silicone caulk remover solvent (DAP Caulk-Be-Gone, $6 to $9) softens the old bead and makes scraping easier. Apply the solvent, wait the time specified on the label (usually 2 to 3 hours), then scrape.
Clean the joint surfaces with a stiff brush and rubbing alcohol or denatured alcohol. Caulk will not bond to dirty, oily, or dusty surfaces. Let everything dry completely before applying new caulk. Applying caulk to a wet joint is a common mistake that causes adhesion failure within months. If you cleaned the joint with water, wait at least 24 hours for the surfaces to dry fully in moderate weather.
For joints in masonry, use a wire brush to remove loose mortar and dust. Blow out the joint with compressed air. If the joint is deep, install backer rod to the correct depth before caulking. The caulk bead should be wider than it is deep. A bead that is deeper than it is wide will split down the center when the joint moves.
Application Technique
Cut the caulk tube tip at a 45-degree angle to a diameter slightly smaller than the joint width. A smaller opening gives you more control. You can always make a second pass, but you cannot take back an oversized bead. Puncture the inner seal with the rod built into most caulk guns or with a long nail.
Hold the gun at a 45-degree angle to the joint and push the caulk ahead of the tip rather than pulling it. Pushing forces the caulk into the joint and makes full contact with both surfaces. Pulling just lays the caulk on top, leaving voids underneath that will eventually fail. Move at a steady pace that lets the caulk fill the joint without gaps or overflow.
Tool the bead within 5 minutes with a wet finger, a caulk finishing tool (Dap Cap, $3), or the back of a plastic spoon. Tooling presses the caulk into the joint edges and creates a smooth, concave profile that sheds water. For acrylic latex caulk, a finger dipped in soapy water works well. For silicone, use a finger dipped in rubbing alcohol. For polyurethane, use mineral spirits on a rag or a tool.
Work in sections of 3 to 4 feet at a time. Apply the bead, tool it, then move to the next section. If you run 20 feet of bead before tooling, the first section will have already skinned over and you will tear the surface trying to smooth it.
Temperature and Timing
Most exterior caulks apply best between 40 and 90 degrees Fahrenheit. Below 40, the caulk is stiff and will not adhere properly to cold surfaces. Above 90, it skins over too fast to tool smoothly. Ideal conditions are dry with moderate temperature and no direct sunlight on the work surface.
Avoid caulking in direct sunlight on hot days because the surface temperature of dark-colored materials can be 30 to 40 degrees above air temperature. A window frame in direct sun on an 85-degree day can reach 120 degrees, which causes the caulk to cure unevenly and may prevent proper adhesion.
Do not caulk before rain. Most exterior caulks need 24 hours to cure, and some polyurethane formulas need 48 to 72 hours. Check the tube for the manufacturer's cure time and weather window. If rain is forecast within the cure window, wait. A bead of caulk that gets rained on before it cures will fail. The best caulking days are dry, overcast, and in the 50 to 75 degree range.
Fall is the best season for exterior caulking in most climates. Temperatures are moderate, rain is often less frequent than in spring, and you seal up the house before winter heating season. Spring is the second-best window. Avoid summer midday caulking unless you are working on shaded surfaces.
Frequently Asked Questions
How Often Should I Recaulk the Exterior of My House?
Inspect annually in the fall before winter. Well-applied polyurethane or silicone caulk can last 15 to 25 years according to manufacturer specs, but sun exposure, joint movement, and material differences cause some joints to fail earlier. Replace any caulk that is cracked, pulled away from the surface, or shows visible gaps. Touch up individual joints as needed rather than recaulking the entire house on a fixed schedule.
Can I Caulk Over Old Caulk?
Not reliably. New caulk will not bond well to old, weathered caulk. Remove the old caulk, clean the joint, and apply fresh. The one exception is if the existing caulk is still firmly bonded and you are just filling a small crack or gap in an otherwise intact bead. In that case, clean the area thoroughly with alcohol, and the new caulk may hold. Full removal and replacement is always the better approach for lasting results.
What Size Caulk Gun Should I Use?
A standard ratchet-drive caulk gun handles 10-ounce tubes, which is the most common size for home use. Spend a few dollars more for a smooth-rod (dripless) gun rather than the cheapest ratchet model. Dripless guns like the Newborn 930-GTD ($12 to $18) or the Dripless ETS2000 ($15 to $20) stop flow immediately when you release the trigger, which prevents the mess that makes people hate caulking. For large jobs, a quart-sized sausage gun holds more material and reduces reloading, but it is overkill for a typical homeowner.