Best Outdoor Silicone Sealant for Weatherproofing: 2025 Expert Review
Oli at OR Electrics
Directory Owner & 18th Edition Electrician
If there is one thing we have in abundance in the UK, it's rain. For homeowners and tradespeople alike, choosing the right outdoor sealant isn't just about making things look tidy; it's about preventing costly water damage. In my line of work, a failed seal around a cable entry can lead to nuisance tripping or, worse, a fire hazard.
I've seen plenty of DIY attempts where the wrong type of sealant was used—often an interior caulk that dissolves in the rain or a cheap silicone that cracks after one frost. Working across Leeds, from the student HMOs in Headingley to commercial units in the city centre, I've learned that you need specific properties for outdoor durability: flexibility, UV resistance, and adhesion to porous materials like brick and stone.
In this review, I'll walk you through three different sealing solutions I've encountered on site: a cost-effective general-purpose option, a high-end hybrid polymer for difficult conditions, and a professional builder's silicone designed for movement.
Live in Leeds?
Need an outdoor socket or security light installed properly?
Get a free quote from OR Electrics.
Specs vs. The Real World
The Spec: "Quick Curing / "Shower Ready in 1 Hour""
"Marketing often claims sealants are waterproof almost immediately."
In the damp UK climate, especially outdoors, most silicones need a full 24 hours to cure properly. If it rains on uncured silicone, the finish ruins. Always check the weather forecast before starting.
The Spec: "Universal / All-Purpose"
"One tube can seal bathrooms, windows, and lead flashing."
Not all silicones are chemically the same. 'Acetoxy' cure smells like vinegar and can corrode lead and copper—a disaster for electricians. 'Neutral' cure is safer for metals and masonry but takes longer to dry.
My Top 3 Recommendations
Three options to cover different needs and budgets
Everbuild General Purpose Silicone Sealant – Waterproof – Clear – 280ml
Everbuild
For straightforward jobs where you need a basic waterproof seal without spending a fortune, this Everbuild General Purpose silicone is the go-to standard. Ideally suited for smooth surfaces like PVCu trims on windows or simple glass sealing.
The Good
- Incredibly low price point
- Contains anti-fungal properties for mould prevention
- Good adhesion to smooth non-porous surfaces (glass, PVCu)
The Bad
- Not the best adhesion on porous brick or stone compared to premium options
- Can have a strong vinegar smell (acetoxy cure) while curing
Installer Tip:
Use this for sealing uPVC trunking or conduit joints outdoors. Ensure the surface is absolutely dry and clean before applying, as this budget option is less forgiving on damp surfaces than hybrid polymers.
Priced at £2.55 at the time of writing
Check Price on AmazonCrystal Clear Construction Sealant & Adhesive All-in-One Hybrid Polymer
Hemway
This isn't just silicone; it's a hybrid polymer. That means it acts as both a powerful adhesive and a flexible sealant. It justifies its higher price tag by being paintable, odourless, and capable of sticking to damp surfaces—a massive bonus for working outdoors in Leeds.
The Good
- Can be applied to damp surfaces (essential for UK winters)
- Paintable (unlike standard silicone)
- Zero shrinking and very high strength
The Bad
- Significantly more expensive than standard silicone
- Can be stiffer to gun out in very cold weather
Installer Tip:
I keep a tube of this in the van for mounting heavy external sensors or EV charger backplates where I don't want to drill excessive holes. It grabs instantly and seals perfectly against rough stone walls where standard silicone might peel away.
Priced at £14.95 at the time of writing
Check Price on AmazonEverbuild Everflex 450 Premium+ Builders Silicone Sealant
Everbuild
This is a 'Low Modulus' Neutral Cure silicone. In plain English, that means it is very stretchy (+/- 25% movement) and chemically neutral. It won't react with metals like lead or copper, and it won't crack when building materials expand and contract in the heat.
The Good
- Neutral cure: Won't corrode copper or lead (vital for electrical work)
- Excellent adhesion to porous surfaces like brick and concrete
- Stays flexible permanently to handle thermal expansion
The Bad
- Takes longer to skin over than cheaper acetoxy silicones
- Not paintable (typical for pure silicone)
Installer Tip:
This is my standard choice for sealing around cable entries through brickwork. Because it's low modulus, it moves with the house and the cable, maintaining the seal year after year. It's also safe to use near lead flashing on roofs.
Priced at £6.39 at the time of writing
Check Price on AmazonFrequently Asked Questions
What is the difference between Low Modulus and High Modulus silicone?
Why can't I use interior caulk outdoors?
Can I paint over outdoor silicone sealant?
Is neutral cure silicone better for electrical work?
How do I ensure a good seal on old brickwork?
Need Professional EV Charging Installation?
Our team at OR Electrics specialises in EV Charging Installation across Leeds.
Get a free quote for professional installation.
View Our EV Charging Installation Service