How to Caulk Gaps Around Windows and Doors

Gaps around windows and doors are a major source of energy loss in Canadian homes, particularly during harsh winters. Properly applied caulk creates an airtight, watertight seal that can reduce heating costs by 10–15%. It also prevents moisture intrusion, which can lead to mould growth and structural damage. Caulking is one of the simplest and most cost-effective home maintenance tasks.

Old caulk dries out and cracks over time, especially on exterior surfaces exposed to Canadian freeze-thaw cycles. House settling creates new gaps as the building shifts. Poor initial caulk application — too thin, wrong type, or applied over dirty surfaces — leads to premature failure. Sun exposure on south-facing walls accelerates deterioration.

A caulking gun (CAD $5–$12), a tube of appropriate caulk (silicone for bathrooms/kitchens at CAD $8–$15, or paintable acrylic latex for interior trim at CAD $5–$10), a utility knife, painter's tape, a damp cloth for smoothing, and a caulk removal tool (CAD $5–$8). For exterior work, use a caulk rated for Canadian weather extremes.

1. Remove all old caulk using a caulk removal tool or utility knife. Clean the surface with rubbing alcohol or a mild cleaner and let dry completely.
2. Apply painter's tape on both sides of the gap for clean lines (especially important for visible interior work).
3. Cut the caulk tube tip at a 45-degree angle — start with a small opening (you can always cut more).
4. Hold the gun at a 45-degree angle and apply steady, even pressure while moving at a consistent speed along the gap.
5. Immediately smooth the bead with a wet finger or caulk smoothing tool.
6. Remove the painter's tape while the caulk is still wet.
7. Allow 24 hours for full cure before exposing to water or painting.
8. For exterior caulking, work on a dry day when the temperature is between 5°C and 30°C.

If you find large gaps (over 1 cm), crumbling window frames, or signs of rot behind the old caulk, a professional should assess the situation. Rotted wood needs to be replaced before caulking — sealing over rot traps moisture and accelerates decay. For second-storey exterior work, hire a professional with proper ladder safety equipment rather than risking a fall.