The sealant round my glass room has gone hard and cracked

What failing sealant actually looks like

Run a fingernail along the joint. Healthy sealant is rubbery and springs back. Failed sealant is hard, sometimes chalky, and may have pulled cleanly away from one face while still gripping the other. That last one is the sneaky failure, because from a distance the joint looks continuous while there is an open channel behind it. On south facing elevations the surface often goes powdery first, because ultraviolet light does the damage long before the weather does.

• Hairline cracks running along the length of the joint
• A gap where the sealant has shrunk back from the brick or glass
• Chalky, dusty surface that marks your finger
• Discolouration, blackening or mould growth along the bead
• Sections that lift away in a strip when touched

Why it fails when it does

Three forces work on it constantly. Ultraviolet light degrades the surface, thermal movement stretches and compresses it every day as aluminium expands far more than brickwork does, and moisture works at any point where adhesion was imperfect. Add poor preparation at installation, sealant applied over dusty or damp masonry, or the wrong product used on a joint that needed a movement grade one, and the life shortens dramatically. Exposure matters too: a joint on a sheltered north wall commonly outlasts one on a hot south facing elevation.

Resealing done properly

The temptation is to run a fresh bead over the old. It looks better for a season and then fails faster than the original, because new sealant cannot bond to a degraded surface and the joint is now too shallow to move. A proper reseal means cutting out the old material completely, cleaning both faces back to sound substrate, letting the joint dry, and applying the right grade for the movement expected. On a wall plate it may also mean fitting or refitting a cover flashing so the sealant is not the only defence.

1. 1Cut out the old bead completely along the full run.
2. 2Clean both faces and let the joint dry fully.
3. 3Check the fixings and substrate now they are visible.
4. 4Apply the correct movement grade sealant in one continuous pass.
5. 5Tool the bead so water sheds off rather than sitting on it.

What happens if it is left

For a season, very little. Over several years, water tracks behind the joint and sits against the masonry and the anchors that hold the structure to the house. That is the point at which a maintenance item becomes a repair: damp in the wall inside, corrosion around fixings, and in the worst cases a wall plate that needs taking off and refixing. The cost difference between a reseal and that outcome is considerable, which is why we would rather people ask early.

The sealant is rarely the expensive part. What the water behind it has reached over several winters can be.

How often to look, and what is fair to expect

A glance along the joints once a year, ideally in autumn before the wet months, is enough. Structures we install carry frame cover of up to 10 years alongside our workmanship guarantee, and sealants and gaskets sit outside that as consumable items maintained over the life of the structure, exactly as they would on any glazed building. On an inherited structure with unknown history, an inspection of the joints is a sensible first job rather than waiting for a stain to appear indoors.