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How to caulk a window frame

The image displays a brick wall with a half window.

Overview

Seal gaps and prevent draughts by caulking your window frames. This easy D.I.Y. project helps keep your home warm and snug while making it more energy efficient.

Safety tip: Always wear the appropriate safety equipment (safety glasses, gloves, ear muffs and a mask, for example) and always follow the instructions for the product or equipment.

Steps

1Check for air leaks

Start by checking for air leaks around the window frame. An easy way to do this is to light a match or candle and hold it near the frame. Any draughts will cause the flame to flicker or go out, indicating there might be a leak.
A hand holding a lighter with flames in front of the window.

2Choose the right type of caulk

Select the right type of caulk for your windows. Look for one that’s suitable for both indoor and outdoor use. Exterior caulk is usually durable, flexible and waterproof polyurethane. For interior gaps, you can use interior or exterior caulk.
A Bunnings team member is holding a tube of Sika Pro+ Polyurethane Sealant.

3Prepare the window

Before you apply the new caulk, you’ll need a clean, dust-free surface for it to stick to. Remove any old caulk from the window frame, then clean the area thoroughly with sugar soap wipes or a damp microfibre cloth.
A person is preparing the window by cleaning the frame with sugar soap wipes.

4Apply masking tape

Apply masking tape along the edges of the window frame, leaving around a 5mm gap. This helps achieve a clean, straight line when applying the caulk.
Applying masking tape along the edges of the window frame.

5Load the caulk gun

Insert the caulk tube into the caulk gun and cut the tip at a 45-degree angle to match the size of the gap. Give it a test on a piece of scrap paper or timber to ensure the gun is ready for a smooth application.
A person cutting the tip of the caulking tube.

6Apply the caulk

Start on the exterior side of the window. Apply a continuous bead of caulk along the seam where the frame meets the wall. Smooth the caulk with a finishing tool to neaten it up and form a tight seal. If you don’t have a finishing tool, you can use your finger. Moisten your fingertip in warm soapy water and drag it with light pressure along the length of the bead of caulk. When you’re done, remove the masking tape and clean up any excess with a damp cloth.
A Bunnings team member is applying the caulk.

7Check the seal

Once the caulk has dried, inspect the exterior window frame for any gaps. Touch up as needed to ensure you have a complete and tight seal around the entire window frame. Once you’re happy, move inside and repeat the process on the interior window frame.
A Bunnings team member is inspecting the window frame.

8Looking for more ways to draught-proof your home?

Health & Safety

Please make sure you use all equipment appropriately and safely when following the advice in these D.I.Y. videos. You need to be familiar with how to use equipment safely and follow the instructions that came with the equipment. If you are unsure, you may feel it is safest to consult an expert, such as the manufacturer or an expert Bunnings Team Member.

Grave health hazards are linked to asbestos, which may be in homes built up to 1990. Health hazards may result from exposure to lead-based paints in older materials and copper chromium arsenic (CCA) treated timber. For information on the dangers of asbestos, lead-based paint and CCA treated timber and tips for dealing with these materials contact your local council's Environmental Health Officer.