gaps between window frames and walls

How to Fill in Gaps Between Window Frames and Walls in 2022 (Step-by-Step DIY Guide) – UK Edition

Save money on your energy bills and improve your home comfort levels in just a few minutes. Sound too good to be true? I recently filled in the gaps around my window frames and not only is my home now fully weatherproof, but I’m also able to turn down my heating and my room looks that little bit neater without those unsightly cracks. 

If you want to fill in the gaps between window frames and walls, follow our easy step-by-step guide for a simple and effective way to a more energy-efficient, cosier home.

Tools & Materials

man using cartridge gun

To complete this job, you won’t need a huge amount of materials or different tools. The vast majority you will probably already own, or you could improvise to save money.


  • Knife
  • Cloth
  • Brush
  • Sealant Cartridge gun
  • Sealant finishing tool (optional but achieves better results)


  • White spirit (or another cleaner)
  • Sealant remover
  • Frame sealant

Alternative Materials

When you’re looking to fill in the gaps around your window frames, you will probably find that there are several different options available. For large exterior gaps, mainly ones wider than one centimetre, you may be better off using mortar. If your gaps are even larger you may wish to consider using expanding foam.

That said in both of these cases you will still need to fully seal off your window frames using window sealant after doing so. My main reasons for choosing frame sealant above other options to fill in the gaps around your windows are:

  • Excellent adhesion – window sealant adheres to wooden, PVC, polycarbonate and metal window frames.
  • Flexible – over time frames and walls can slightly shift, contact and expand. As window sealant remains permanently flexible, you won’t have to repeat the job again anytime soon. In fact, my window sealant even came with a 25-year guarantee.
  • Waterproof – keep your home weather-tight. 
  • Easy to apply – handy cartridge format means you’ll need fewer tools and save application time too.

Fill in Gaps Between Window Frames and Walls – Step-by-Step Guide

All set to get started? Simply follow the steps below for a quick and easy way to get those gaps around your window frames filled in no time.

1. Check your equipment

Before starting any job I like to gather up everything I’m going to need, so I can make sure that I not only have all the essentials but also that I have them to hand. Use the list above and don’t start until you’ve got everything ready to go.

2. Clean around the frame

You’d be surprised how many people forget this seemingly insignificant but absolutely crucial step. In order to effectively seal your window frame, you need the area to be completely dry and free of dirt, dust, old sealant and whatever else. If you don’t complete this step then chances are your sealant won’t adhere correctly to your window frames and walls.

Dampen a cloth with white spirit and rub the entire area around the frame you are going to be sealing. This will get rid of any grease and dirt. If you’re just moving in and the area’s really dirty, you may want to brush off any dirt, cobwebs or flaking paintwork before cleaning. If there is old sealant that is refusing to budge, use sealant remover to help you to get it off. 

Before continuing, give your nice clean window frames a few minutes to dry completely. Depending upon your frame material, this could take up to 15 minutes.

3. Prepare sealant cartridge

Cut the tip off the sealant cartridge above the screw thread. Remove the nozzle head and cut it at a 45-degree angle. Depending upon how wide the gap is, you will need to cut nearer to the nozzle tip for a narrow bead or higher up for a wider bead. Screw on the nozzle and insert your cartridge into the gun.

4. Apply sealant

Apply your sealant by pulling the gun trigger. You want to aim your nozzle into the gap. Try to apply the sealant in a smooth, continuous movement all the way around the entire frame, even if the gap is only located on one side. This will ensure that your sealant will last longer and stick better. 

5. Smooth

If necessary, smooth over your bead of window sealant with a sealant finishing tool for a perfect finish. I find that simply wetting my finger and running it lightly over the bead works best for me. 

Once you’re happy with your results, simply let your sealant dry as recommended by the manufacturer then paint over if needed. 

If you want to see these steps in action, please watch the video below:

YouTube player

Fill in Gaps Between Window Frames and Walls – Final Thoughts

As the saying goes, there’s no place like home. Don’t suffer draughts or waste money and energy, get those gaps around your windows sealed today. Doing so will also ensure that your frames and walls remain in excellent condition. Best of all, it’s inexpensive, easy to do and takes little time.