How to seal around uPVC window frames

Sealing around uPVC window frames helps prevent draughts, heat loss and water ingress, improving comfort and energy efficiency throughout the home.

What you’ll need

uPVC-compatible sealant (silicone, hybrid polymer or paintable frame sealant), caulking gun, wipes or damp cloth, masking tape (optional).

Preparation

• Remove any old sealant, dust, grease and dirt from the frame and surrounding surface.
• Clean with a damp cloth or uPVC-safe cleaner and allow surfaces to dry completely.
• Apply masking tape along the frame and wall, leaving a 5–10mm gap for a neat finish.
• For gaps wider than 12mm, insert a foam backer rod before sealing.

Application

• Cut the nozzle at a 45° angle to suit the joint size and load the cartridge into the gun.
• Apply a continuous, even bead of sealant along the joint, working smoothly from top to bottom.
• Tool the sealant immediately using a damp finger, soapy water (for silicone), or a smoothing tool to press it firmly into the gap.

Finishing

• Remove masking tape while the sealant is still wet.
• Wipe away excess sealant or residue with a damp cloth.
• Allow the sealant to cure for 12–24 hours before touching or exposing to moisture.

Key tips

• Use low-modulus neutral cure silicone or hybrid sealants for exterior frames.
• Choose paintable frame sealant for interior joints that will be painted.
• Seal during dry conditions for best adhesion and performance.
• Inspect seals annually and replace any that show cracking or shrinkage.