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How to Caulk Windows and Doors: A Homeowner's Guide

Where to caulk, which caulk to buy, and the gaps you should leave open, so your windows and doors keep water and drafts out.

Caulk is one of the cheapest ways to protect your home. A good bead around windows and doors keeps out rain, drafts and bugs. When caulk cracks and pulls away, water gets behind trim and siding, and that's how rot starts. Here's how to caulk windows and doors the right way, and the spots you should leave alone.

Where to caulk

Outside

• Where window and door trim meets siding or brick
• Where trim boards meet each other at corners
• Gaps around exterior door thresholds where they meet the siding
• Around hose bibs, dryer vents and pipes that come through walls

Inside

• Where window and door trim meets the wall
• Small gaps between trim and drywall before painting
• Around window stools and sills

Where NOT to caulk

This matters as much as where to caulk. Some gaps are there on purpose so water can get out.

• Weep holes in brick. Small gaps along the bottom of brick walls, often above windows and doors, let moisture drain out. Don't fill them.
• Window weep slots. Many vinyl and aluminum windows have small slots at the bottom of the frame for drainage. Keep them open.
• The bottom edge of some trim and siding where water is meant to drain out, like the bottom edge of lap siding.
• Around the bottom of a storm window, if it has drain holes.

Sealing these traps water inside the wall, which is worse than no caulk at all.

Pick the right caulk

Read the label. Look for:

• Exterior use for outside work. It handles sun, heat and movement better.
• Paintable if you plan to paint. Pure silicone usually isn't.
• Flexibility. Wood and siding expand and shrink with Georgia's heat and humidity. A flexible, high-movement sealant lasts longer.

Common choices:

• Siliconized acrylic latex. Easy to use, cleans up with water, paintable. Good for interior trim and many exterior joints.
• Polyurethane or hybrid sealants. Tough, flexible and long-lasting outside. Messier to work with.
• 100% silicone. Great for wet areas like tubs and around some windows, but most paint won't stick to it.

How to caulk

1. Remove the old caulk

Cut and scrape out old, cracked caulk with a utility knife or caulk removal tool. Get it all out if you can. New caulk won't bond to old.

If your home was built before 1978, painted caulk and trim may contain lead. Avoid dry sanding, and see our older home repairs guide for safe practices.

2. Clean and dry the joint

Brush out dust and debris. Wipe the joint and let it dry. Caulk won't stick to wet, dusty or mildewed surfaces. Clean mildew first and let it dry fully.

3. Fill deep gaps first

For gaps deeper than about a quarter inch, push in foam backer rod first. It keeps the caulk from sinking too deep, saves caulk and helps the bead flex the right way.

4. Apply a steady bead

Cut the tube tip at an angle, small at first. Hold the gun at an angle and push or pull a steady bead along the joint. Work in short sections.

5. Tool it smooth

Smooth the bead with a damp finger, a wet rag or a caulk tool. This presses caulk into the joint. Wipe off extra right away.

6. Let it cure

Check the label for temperature range and drying time. Don't caulk outside right before rain. Wait the recommended time before painting.

When to check

Look at your caulk in spring and again in fall. Hot summers and sunny walls wear caulk out fastest. Our fall home maintenance checklist is a good time to do a full walk-around.

When caulk isn't enough

If you find soft wood under old caulk, the trim needs repair first. Caulk won't fix rot. And if a door sticks, won't close tight or leaves daylight around it, the door or weatherstripping may need attention.

We can help

We recaulk trim as part of exterior painting, door repair and trim and baseboard work. Text a photo to (706) 594-5049, or use our free estimate form for a free estimate.