In winter, window seals work at their limit: frost and wind outside, warm dry air from the radiators inside and condensation on the glass and frame. These swings make rubber harden, turn porous and crack. The results are familiar: the sash freezes shut, the frame lets in a draught, dark mould spots appear on the reveals and the heating warms the street.
Replacing a seal is a chore, but looking after it takes minutes. The easiest approach is to combine it with cleaning the windows before the cold sets in and to repeat it in midwinter.
What you will need
Important: Do not use harsh cleaners, solvents, abrasive sponges or sharp tools: they make rubber porous and tear it. Never force a frozen sash open, as you may rip the seal out, and never heat the frame with an open flame.
Step 1
Check the condition of the seals
Inspect the rubber all round the sash and frame. Cracks, missing pieces and splits are easy to spot. Press with a finger: a healthy seal is soft, smooth and springs back. If the rubber is hard and barely gives, it is no longer sealing properly.
Another warning sign is a draught near the frame when the window is shut, especially on windy days.
Step 2
Wash the seal and frame
Wipe the rubber and the frame rebate with a cloth dipped in warm soapy water. Do not scrape at old dirt: soak it and remove it with gentle strokes, repeating several times. Clean corners and folds with cotton buds.
Do not forget the drainage holes at the bottom of the frame: water that sits there freezes and splits the rubber.
Step 3
Dry thoroughly
After washing, dry the rubber and frame completely with a clean cloth, including hard-to-reach spots. Moisture left on the seal will either freeze and lock the sash in winter or feed mould, which spreads quickly and is bad for your health.
Leave the sash ajar for 10-15 minutes so everything dries out fully.
Step 4
Apply silicone protection
Spray WD-40 Specialist Silicone onto a microfibre cloth and wipe it along the entire seal. You can also spray directly onto the rubber from 15-20 cm and then spread it evenly with the cloth.
Silicone keeps rubber supple in the cold, displaces moisture and stops the sash freezing to the frame. Wipe off any excess; there should be none on the glass.
Step 5
Free a frozen window the right way
If a sash has frozen shut, raise the room temperature and wait, or warm the frame perimeter with a hairdryer on a moderate setting without aiming it at one spot for long. Then pull the handle smoothly.
Once the window opens, wipe away the meltwater and treat the seal with silicone again. The handle and hardware can be lubricated with WD-40 Smart Straw through the straw so condensation does not make the mechanism stiff.
Tip: Condensation is not only about the rubber: ventilation matters too. Airing the room for 5-10 minutes several times a day lowers indoor humidity and reduces the water collecting on the frames.
What next
Treat the seals with WD-40 Specialist Silicone before the cold weather and again in midwinter, especially if the rubber is old or the windows often freeze. Replace a damaged seal by removing the old one completely, cleaning the groove and fitting the new one, then look after it the same way.
These uses come from the experience of WD-40 users in many countries. Always follow the instructions and warnings on the product label.
More guides in «How to use».