Facade Sealant Replacement: When to Reseal and How It Is Done

Resealing is not a touch-up

Sealant joints on a commercial facade are the cheapest line in the original package and one of the most common reasons it leaks a decade later. When they fail, the instinct is a quick fix: send someone up in a cradle with a cartridge gun and run a fresh bead over anything that looks cracked.

That is the misconception that makes resealing expensive. New sealant over old does not bond reliably, and a joint resealed without preparation fails again, usually within a few monsoons. Facade access is the costly part of the work, whether by building maintenance unit, cradle, rope access or scaffold, so doing the job twice means paying for access twice. Meanwhile water keeps getting in behind the cladding, into the slab edge and onto the ceilings and floors inside.

There is a second risk. Some silicone on a glass facade is structural: it holds the glass to the frame. A crew that cannot tell the difference, or that cuts too deep, can damage the bond that keeps glass on the building. A proper resealing programme starts by knowing which joints are which.

Signs that sealant joints need attention

The last row matters. Facades leak at many interfaces, including flashings, gaskets, stack joints and penetrations, and sealant is only one of them. Before committing to a reseal, it is worth reading how leak paths are traced in where facades leak: joints, sills and penetrations.

Age is not the trigger; condition is

There is no universal replacement interval. A sealant's life depends on the product, how much ultraviolet light it gets, how much the joint moves with temperature and building movement, whether the joint was designed wide enough for that movement, and how well it was installed. Manufacturers give their own expectations for their products.

What should trigger a programme is evidence. A competent inspection samples joints across each elevation and orientation, records the condition, and tests adhesion. ASTM C1521 describes field methods for evaluating the adhesion of installed weatherproofing sealant joints, in which the bead is cut and pulled to see whether it lets go of the substrate or tears within itself. That failure mode tells you what went wrong: poor adhesion points to preparation, primer or compatibility; cohesive tearing points to movement, joint design or ageing.

When failures are widespread across an elevation, chasing individual leaks becomes more expensive than a planned reseal. When the joint design itself is wrong, for example joints too narrow for the movement they take, resealing with the same geometry repeats the failure, and the decision may move towards facade retrofit and recladding.

Weatherseal versus structural silicone: know which you are touching

A silicone weatherseal closes the gap between panels against water and air. It carries no load, and it is the joint a resealing programme replaces.

Structural silicone glazing is different. It bonds glass or panels to the frame and transfers wind load to the structure. ASTM C1401 is the guide for structural sealant glazing, and it treats the structural bond as an engineered element designed by calculation and installed under controlled conditions. On many curtain walls the structural silicone sits directly behind the weatherseal, sometimes only millimetres away.

The rules that follow are simple:

• Do not cut, remove or replace structural silicone as part of a weatherseal job. Any concern about it goes to the facade engineer, who assesses it and decides on remedial design and temporary retention if needed.
• Identify the joint types from the shop drawings before work starts, and mark them on the joint map.
• Check compatibility. The new weatherseal will touch the structural silicone, gaskets, setting blocks, insulating glass edge seals and coatings. Incompatible materials can soften, stain or break the bond. The sealant manufacturer should confirm compatibility in writing, usually after testing samples of the actual substrates.

How a proper resealing programme works

ASTM C1193, the standard guide for use of joint sealants, sets out the principles of joint design, preparation and installation. A typical programme follows them in this order:

1. Survey and map. Record every joint type, condition and location by elevation and floor, with photographs.
2. Trial area. Cut out and reseal a small area using the proposed method, cleaner, primer and sealant. Let it cure and test adhesion before approving the method for the whole building.
3. Cut out completely. Remove old sealant and backer rod without damaging glass coatings, anodised or painted finishes, gaskets or structural silicone.
4. Clean. Remove residue back to sound substrate. Non-porous surfaces such as glass and metal are commonly cleaned by solvent wipe followed immediately by a dry cloth, the two-cloth method, using the cleaner the manufacturer names.
5. Prime where the manufacturer requires it for that substrate, within the time window stated.
6. Fit backer rod of the type and size specified. ASTM C1330 covers cylindrical sealant backing; it sets the sealant depth and stops adhesion to the back of the joint. Closed-cell rod punctured during installation can release gas into curing sealant and cause bubbles.
7. Apply and tool. Fill the joint and tool it to the profile that gives two-sided adhesion and lets the bead stretch and compress.
8. Protect and cure. Keep the joint free of water, dust and movement while it cures, within the manufacturer's temperature and humidity limits.
9. Test and record. Adhesion tests on a sample of new joints, a field water test on representative areas, and an updated joint map.

The sealant itself should be specified to ASTM C920, which classifies elastomeric joint sealants by type, grade, movement class and use, with the movement class chosen for the joint, not the other way round.

Access, weather and occupied buildings

Most of the cost is getting people safely to the joints. Building maintenance units, cradles, rope access, mast climbers and scaffolding each suit different facades and budgets, and the choice affects the programme as much as the sealant work; the options are covered under facade access and maintenance.

Sealant needs dry, clean substrates within the manufacturer's application conditions, so resealing belongs in the dry season, well before the monsoon. In an occupied building, plan for solvent and primer fumes near air intakes and openable windows, exclusion zones below the work, and notice to tenants on each floor.

Common mistakes

• Running new sealant over old. It does not bond and hides the failure.
• Skipping the trial area and adhesion test. The whole building is resealed with a method that does not stick.
• Cutting into structural silicone while removing the weatherseal.
• Mixing products without the manufacturer's written compatibility check.
• Sealing weep holes and drainage slots on a drained facade, trapping water.
• Working on damp or dusty substrates to keep to a cradle booking.
• Keeping the same joint width where movement tore the original bead.
• No records. The next inspection starts from nothing.

What to ask a resealing contractor

• How will you distinguish weatherseal from structural silicone, and who has checked the shop drawings?
• What did the adhesion tests on existing joints show, and what failure mode?
• Will there be a trial area, and how will its adhesion be tested?
• Has the sealant manufacturer confirmed compatibility with the substrates and adjacent materials in writing?
• What cleaner, primer, backer rod and sealant will be used, to which standards?
• What access method, when, and what is the plan for weather?
• What testing and records will be handed over at the end?

Standards referenced

Joint sealant design, preparation and installation in ASTM C1193; elastomeric joint sealant classification in ASTM C920; field adhesion testing of installed sealant joints in ASTM C1521; cylindrical sealant backing in ASTM C1330; structural sealant glazing in ASTM C1401; field water penetration testing in ASTM E1105. Joint design, product selection, compatibility, assessment of any structural silicone, and the test method and acceptance criteria for a specific facade must be established by the project's facade engineer and the sealant manufacturer.