Exterior Caulking: Where, How, and Which Type

Types of Exterior Caulk

Silicone is the most durable exterior caulk. It stays flexible for 20 or more years, handles extreme temperatures, and won't shrink. The downside: it can't be painted and it doesn't adhere well to wood. Use silicone for glass-to-metal joints, flashing seams, and anywhere you don't need paint coverage.

Polyurethane caulk is the best all-around choice for most exterior joints. It's paintable, bonds strongly to wood, masonry, metal, and vinyl, and lasts 15 to 25 years. It's harder to tool than silicone and cleans up with mineral spirits rather than water. Siliconized acrylic latex is the easiest to apply and clean up, but it only lasts 5 to 10 years outdoors and isn't suitable for joints with significant movement.

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.

Don't caulk the bottom edge of siding courses — water that gets behind the siding needs a path to drain out. Don't caulk weep holes on brick veneer walls. Don't 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.

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 scrapes out the bulk. A utility knife cuts through stubborn sections. For silicone caulk removal, a silicone caulk remover solvent softens the old bead and makes scraping easier.

Clean the joint surfaces with a stiff brush and rubbing alcohol or denatured alcohol. Caulk won't 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.

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 can't 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. Pulling just lays it on top. 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, or the back of a plastic spoon.

Temperature and Timing

Most exterior caulks apply best between 40 and 90 degrees Fahrenheit. Below 40, the caulk is stiff and won't adhere properly. Above 90, it skins over too fast to tool smoothly. Ideal conditions are dry with moderate temperature. 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.

Don't 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.

Frequently Asked Questions