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Professional Guide

Best Exterior Glazing Silicone for Windows & Garden Rooms: 2025 Expert Review

DJ

DR Joinery

Expert Joiner & Timber Sports Specialist

Published 16 December 2025

Choosing the right silicone for exterior glazing isn't just about picking a tube off the shelf. If you get it wrong, water penetrates the joinery, sits in the rebate, and before you realise it, your expensive timber frames are rotting from the inside out.

In my trade, particularly when building garden studios or restoring sash windows in York's older properties, the sealant is the first line of defence. Timber expands and contracts with the seasons, and standard rigid fillers simply crack and fall out.

In this review, I've categorised three glazing silicones I regularly see on site. I'll explain which ones are suitable for quick repairs and which ones I'd trust for a full glazing installation.

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Specs vs. The Real World

The Spec: "Waterproof Claims"

The Theory

"All silicone tubes claim to be 100% waterproof and weatherproof."

The Reality

Every silicone acts as a barrier, but the failure point is adhesion. If the timber is damp or dirty when applied, even the best silicone will peel away, letting water track behind it.

The Spec: "Multi-Purpose vs Specialised"

The Theory

"General purpose silicone can supposedly be used for everything from bathrooms to windows."

The Reality

For exterior glazing, you need a high-modulus or specific glazing silicone that can withstand UV light and significant temperature shifts without becoming brittle.

My Top 3 Recommendations

Three options to cover different needs and budgets

Everbuild General Purpose Silicone Sealant – Waterproof – Brown – 280ml

Budget Pick
Everbuild General Purpose Silicone Sealant – Waterproof – Brown – 280ml

Everbuild

This is a bread-and-butter sealant for general maintenance. While I wouldn't use it for structural glazing on a high-end oak garden room, it's perfectly adequate for sealing gaps around frames or minor repairs where cost is the main factor.

Price£2.87 (at time of writing)
TypeGeneral Purpose
ColourBrown (suits timber)
The Good
  • Very affordable option for basic sealing
  • Brown colour blends well with stained timber sheds and fences
  • Contains anti-fungal properties to stop mould growth
The Bad
  • Less flexible than specialist glazing silicones
  • Curing time can vary in cold Yorkshire weather

Installer Tip:

Use masking tape on the glass and the timber frame before applying. This 'budget' silicone can be quite sticky and messy, and a clean tape line ensures a professional-looking finish.

Priced at £2.87 at the time of writing

Check Price on Amazon

Everflex 200 Contractors LMA Silicone Sealant – Transparent – 295ml

Quality Option
Everflex 200 Contractors LMA Silicone Sealant – Transparent – 295ml

Everbuild

The 'LMA' stands for Low Modulus Acetoxy. This is a step up from the general purpose tube. It offers better flexibility, which is crucial for timber garden studios that shift significantly between summer and winter.

Price£6.05 (at time of writing)
FlexibilityEnhanced (resists expansion)
Cure TypeQuick Curing
The Good
  • Quick curing is excellent when rain clouds are gathering
  • Good flexibility prevents the seal from cracking
  • Transparent finish is ideal for glass-to-glass joints
The Bad
  • Strong vinegar smell while curing (acetoxy)
  • Ideally needs a dry day to apply properly

Installer Tip:

Because this skins over quickly, don't try to seal the whole window at once. Run one bead, tool it off immediately with a finishing tool or a soapy finger, then move to the next edge.

Priced at £6.05 at the time of writing

Check Price on Amazon

Everflex 225 Contract Industrial & Glazing Silicone – Transparent

Problem-Solving Pick
Everflex 225 Contract Industrial & Glazing Silicone – Transparent

Everbuild

This is specifically formulated for glazing. If you are bedding glass into a timber rebate or sealing aluminium capping on a garden room, this is the product to trust. It handles high temperatures well, which is vital for south-facing windows.

Price£4.48 (at time of writing)
Key FeatureIndustrial & Glazing Specific
Temp ResistanceUp to 200˚C
The Good
  • Specifically designed for glazing applications
  • Excellent adhesion to glass, aluminium, and timber
  • Fast drying (skins in 10 mins) helps in changeable weather
The Bad
  • Requires a steady hand as it sets fast
  • Not paintable (like most silicones)

Installer Tip:

When using this for 'bedding in' (placing glass into the frame), apply a continuous bead around the rebate. Don't leave gaps, or water will pool at the bottom and rot the timber joinery.

Priced at £4.48 at the time of writing

Check Price on Amazon

Frequently Asked Questions

Can I paint over glazing silicone?
Generally, no. Silicone repels paint. If you need to paint the frame, do it before applying the silicone, or use a specific 'paintable caulk' for the frame exterior, though caulk isn't suitable for the glass-to-frame seal itself.
How often should I replace silicone on my garden studio windows?
In York, with our wet winters and occasional hot spells, inspect them annually. A good silicone job should last 10-20 years, but if you see peeling or black mould getting underneath, it needs stripping out and replacing immediately to save the timber.
What is the difference between Low Modulus and High Modulus silicone?
Low Modulus (LMA) is stretchier and places less stress on the joint, making it better for exterior window frames and garden studios where materials expand and contract. High Modulus is stiffer and often used indoors for sanitary ware.
How do I remove old silicone from a timber frame?
Don't just scrape it; you'll damage the wood. Cut the bulk away with a sharp blade, then use a dedicated silicone remover gel to break down the residue. Ensure the timber is bone dry before applying new sealant.
Why has my silicone turned black?
That's black mould. It happens if water sits on the sealant or if cheap silicone (with low anti-fungal properties) was used. Using a quality anti-fungal glazing silicone and ensuring water can run off the sill is the best prevention.

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