Best Sealants for Leaky Windows in 2026 — UK Buyer’s Guide
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Photo by Allen Perper
on Unsplash.
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Leaky windows need a sealant that stays flexible, bonds well and copes with British weather. The wrong product can crack, peel or block future maintenance.
This guide covers reliable sealants for internal and external window repairs, with choices for quick fixes, long-lasting weatherproofing and neat finishing.
Our Top Picks
£4-£8
Everbuild Everflex 195 Universal Silicone Sealant
“A versatile, trusted silicone for general window sealing jobs.”
Everbuild Everflex 195 is a solid all-rounder for sealing around window frames where flexibility and weather resistance matter. It applies neatly and remains elastic enough to handle movement.
It is good value and widely available in the UK, which makes it a sensible pick for both DIYers and trades. It is not paintable, so it is best used where the finish can remain as applied.
- Flexible and weather-resistant
- Good value
- Widely available
- Not paintable
- Needs careful application for a neat finish
Best for: General external sealing around window frames.
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£10-£15
CT1 Sealant and Adhesive
“A strong multi-purpose sealant that grips well on tricky surfaces.”
CT1 is popular for awkward leaks because it bonds to a wide range of materials and remains tough in wet conditions. It is useful for windows with mixed substrates such as uPVC, aluminium and masonry.
It is pricier than basic silicone, but the versatility and durability make it worthwhile for stubborn leaks. It is especially useful when you want one product for several small repair jobs.
- Excellent adhesion
- Good on mixed materials
- Durable and weatherproof
- More expensive than basic sealants
- Can be messy if over-applied
Best for: Tricky leak repairs on mixed-frame windows.
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£3-£6
No Nonsense Trade Silicone Sealant
“A budget-friendly option that does the job for routine sealing.”
No Nonsense Trade Silicone Sealant is a practical choice for straightforward window sealing where you want decent performance without paying premium prices. It is easy to use and suitable for common draught and rain ingress issues.
It will not match specialist products for versatility, but it offers fair durability for the money. For basic DIY repairs, it is an easy product to keep in the toolbox.
- Low cost
- Easy to apply
- Good for simple repairs
- Less premium finish
- Limited versatility
Best for: Budget-conscious DIY fixes on sound window frames.
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£8-£13
Soudal Fix All Crystal
“A clear, neat sealant that is handy when appearance matters.”
Soudal Fix All Crystal is useful where you want a clear finish around internal or visible window joints. It offers strong adhesion and flexibility while keeping the repair discreet.
Its cleaner appearance makes it appealing for visible areas, though it still needs careful surface preparation for the best result. It is a strong mid-range choice for tidy DIY work.
- Clear finish
- Flexible and durable
- Good for visible repairs
- Surface prep is important
- Not the cheapest option
Best for: Neat sealing where appearance is as important as performance.
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£10-£16
Dowsil 791 Silicone Weatherproofing Sealant
“A premium weatherproof sealant for demanding exterior joints.”
Dowsil 791 is designed for weather exposure and movement, making it a strong choice for exposed external window joints. It remains flexible and offers reliable resistance to the elements.
It is a premium product, but the performance is reassuring on properties that see heavy rain and wind. For long-term external sealing, it is one of the safest bets.
- Excellent weather resistance
- Long-lasting flexibility
- Reliable for exterior use
- Higher price
- Best used with good application technique
Best for: Exposed external window seals needing durable weatherproofing.
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What to Look For — Buyer’s Guide
What matters
Choose a sealant based on where the leak is: external joints need weatherproof, flexible products, while internal cosmetic repairs may benefit from paintable or clear options.
Good surface prep matters more than brand alone. Clean, dry and degreased edges help sealants bond properly and last longer, especially on old frames.
Our Verdict
The best sealant for leaky windows is the one matched to the frame, exposure and finish you need, with flexibility and adhesion doing most of the work.
