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

> Facade sealant replacement means cutting out failed weatherseal joints completely, cleaning and priming the joint faces, fitting a backer rod, and applying and tooling compatible new sealant, then testing adhesion and water tightness. It is triggered by loss of adhesion, splitting, hardening or leaks, not by age alone. Structural silicone holding glass is a separate matter for the facade engineer.

## 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

| Sign | What it usually means | Next step |
| --- | --- | --- |
| Sealant pulled away from one side of the joint | Adhesive failure: preparation, primer or compatibility | Adhesion test; check the substrate and original method |
| Split down the middle of the bead | Cohesive failure: joint too narrow for its movement, or sealant at end of life | Check joint width against expected movement |
| Hard, chalky or crazed surface | UV and weathering ageing | Assess remaining elasticity across the elevation |
| Sticky, soft or staining sealant | Incompatible materials or wrong product | Identify products in contact; manufacturer review |
| Bubbles or voids in the bead | Punctured backer rod or moisture during application | Cut out a sample to inspect |
| Sealant painted over, or patched on top | Previous quick fixes | Treat as failed; cut out |
| Leaks on storm-facing elevations | Joint failure is one possibility among several | Diagnose the leak path before resealing |

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](/blog/where-facades-leak-joints-sills-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](/services/facade-glazing/facade-retrofit-and-recladding).

## Weatherseal versus structural silicone: know which you are touching

A [silicone weatherseal](/glossary/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](/glossary/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](/services/facade-glazing/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.

## Frequently asked questions

### How often do facade sealants need replacing?

There is no fixed interval. Sealant life depends on the product, sun exposure, the movement the joint takes, the joint design and how well it was installed. Manufacturers state their own expectations. The practical trigger is condition: when inspection and adhesion testing show joints are failing across an elevation, a planned reseal is due, rather than chasing individual leaks.

### Can new sealant be applied over the old sealant?

Generally no. New sealant does not bond reliably to old, weathered sealant, and a bead over a failed joint hides the failure rather than fixing it. The old sealant is cut out, the joint faces are cleaned back to sound substrate, and the new sealant is installed as a complete joint. Any exception should come in writing from the sealant manufacturer after testing.

### Is the silicone holding the glass replaced at the same time?

No, not as part of a weatherseal job. Structural silicone that bonds glass to the frame carries wind load and is designed and installed under controlled conditions. Cutting or disturbing it is a safety matter. If structural silicone shows signs of failure, the facade engineer assesses it separately and decides on any remedial design and temporary measures.

### What is an adhesion test and why does it matter?

ASTM C1521 describes field tests in which a cured sealant bead is cut and pulled by hand to see whether it fails by losing adhesion to the substrate or by tearing within the sealant. Done on existing joints, it shows how the old sealant failed. Done on trial joints, it confirms that the cleaning, primer and sealant chosen actually bond to that substrate.

### Can resealing be done while the building is occupied?

Usually yes, since most of the work is outside. It needs safe access by building maintenance unit, cradle, rope access or scaffold; control of solvents and primers near open windows and air intakes; protection of people and vehicles below; and programming around weather, because sealant must be applied to dry surfaces within the manufacturer's conditions.

### How do we know the reseal has worked?

By records and testing, not appearance. Adhesion tests on a sample of new joints, a joint map showing what was done and where, and a field water test on representative areas, such as ASTM E1105 with the test method set by the facade consultant. Keep the product data, batch numbers and test results for the next inspection.

## Sources

- [ASTM C1193](https://www.astm.org/products-services/standards-and-publications.html) — Standard guide for use of joint sealants
- [ASTM C920](https://www.astm.org/products-services/standards-and-publications.html) — Standard specification for elastomeric joint sealants
- [ASTM C1521](https://www.astm.org/products-services/standards-and-publications.html) — Standard practice for evaluating adhesion of installed weatherproofing sealant joints
- [ASTM C1330](https://www.astm.org/products-services/standards-and-publications.html) — Standard specification for cylindrical sealant backing for use with cold liquid-applied sealants
- [ASTM C1401](https://www.astm.org/products-services/standards-and-publications.html) — Standard guide for structural sealant glazing
- [ASTM E1105](https://www.astm.org/products-services/standards-and-publications.html) — Field determination of water penetration of installed exterior windows, skylights, doors and curtain walls

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Source: https://hagerstone.com/blog/facade-sealant-replacement-when-and-how