Coatings and interior systems · Paints & Coatings
Elastomeric Crack Bridging Facade Coating
This entry explains what an elastomeric coating is for, why crack bridging and vapour openness pull against each other, and what has to be established before a wall is wrapped in one.
Educational reference entry. Suitability depends on the complete assembly, substrate, exposure, installation method, manufacturer documentation, local requirements and qualified professional review.
Overview
What elastomeric coating is
An elastomeric facade coating is a heavily filled, flexible coating, usually built on an acrylic or modified acrylic binder chosen for extensibility rather than hardness. It is applied at a much greater film build than ordinary decoration, so the dried coating has real substance and can stretch. The point of that combination is to carry the coating across fine cracking in the surface below without splitting along it.
That is the difference from the exterior masonry paint entry. Ordinary masonry paint is a thin decorative film that follows the substrate faithfully; where the wall cracks, the paint cracks with it and the crack reappears within a season or two. An elastomeric coating has enough thickness and elasticity to span the same movement. It is a specific answer to a specific defect rather than a better version of masonry paint.
The price of that thickness is permeability. A heavy, continuous, flexible film is markedly less vapour open than a mineral or silicone resin coating, which is the exact opposite direction from those families. A wall that is wet, or that gets wet from behind, is therefore the wrong place for it: moisture held in the masonry drives blistering, delamination and frost damage. The coating also hides the crack rather than explaining it, and it is difficult to remove or overcoat later.
Terminology
Common names and aliases
These names describe the same thing. The library keeps one entry per material so that an acronym, a trade name or a regional spelling never becomes a second, thinner page.
- elastomeric wall coating
- flexible masonry coating
- crack bridging coating
Applications
Common applications
Where this material is typically encountered. A typical application is not a statement that it suits your project.
- Rendered elevations showing fine, stabilised surface cracking that keeps reappearing after redecoration.
- Facades of buildings with a history of thermal movement in the render finish.
- Exposed elevations where an existing coating has repeatedly failed along the same lines.
- Refurbishment of rendered blocks where a uniform, heavier finish is being applied across a whole facade.
Consideration
Where it is commonly considered
- Where fine cracking has been investigated, its cause understood, and the movement judged to be stable.
- On dense, low permeability backgrounds where a less vapour open coating changes little about the wall.
- Where the alternative is repeated redecoration that fails along the same cracks every few seasons.
- As part of a wider repair strategy, rather than as a substitute for one.
Professional review
Where additional professional review is especially important
These are the situations where the answer depends on the specific building, and where a qualified professional should be involved before anything is decided.
- On solid traditional walls that depend on drying outwards through the face.
- On lime render, historic fabric and other permeable constructions, where the film changes their moisture behaviour.
- Where cracking is structural or progressive, since covering it removes the evidence and not the cause.
- On walls with rising, penetrating or condensation related damp that has not been resolved.
- Where nobody has established whether the substrate can hold the weight and adhesion of a heavy film.
- On previously unpainted masonry, where the decision is close to irreversible.
Properties
Key properties to discuss
Qualitative topics worth raising. Measured values, classes and grades come from the manufacturer's technical documentation for the specific product, not from a reference page.
- Moisture behaviour
- The heavy flexible film reduces how readily the wall dries through its face. On any construction that relies on outward drying, that is the single most important consequence of using this coating.
- Substrate dependency
- The background must be sound, stable and able to hold a heavy film. Poorly adhered existing coatings, friable render and salt affected surfaces will push the coating off regardless of its elasticity.
- Weathering and exposure
- Extensibility changes with temperature and with age, and coatings generally harden as they weather, so the crack bridging behaviour of an old film is not that of a new one.
- Appearance
- Film build softens and rounds sharp arrises and fine texture, which alters the character of a moulded or textured render. Smooth and textured versions look quite different at a distance.
- Repairability
- Patch repairs to a heavy textured film rarely blend, and localised damage tends to require working to a natural break rather than touching in.
- Maintenance
- Once a wall is coated this way, redecoration is largely committed to compatible products, and removal is difficult, messy and potentially damaging to the render beneath.
- Documentation
- Crack bridging capability, substrate requirements and permeability are all properties of the specific product and are only reliable from its own technical documentation.
Exposure
Exposure and environmental conditions
- Has the cause of the cracking been investigated, or is the coating being used to make it disappear?
- Is the wall wet, and if so, where is the water coming from and what happens to it once it is sealed in?
- How exposed is the elevation to driving rain, sun and freeze thaw cycling through the year?
- Is the construction solid or cavity, and how does that change the consequence of a less permeable film?
- Are there internal signs of damp on this wall that anyone has looked for?
Assembly
Substrate and system dependencies
What this material sits on, is fixed to or depends on. This is usually where performance is won or lost.
- The render below must be sound and adhered, because a heavy coating on failing render brings it off the wall.
- Existing coatings need adhesion testing, since the new film is heavier than what came before.
- Movement joints in the building have to be carried through the coating rather than covered by it.
- Salts, efflorescence and damp affected areas need resolving first, as they will not be contained by a film.
- Details at copings, sills, abutments and openings decide whether water gets behind the coating.
Appearance
Appearance and finish considerations
- The heavier film rounds off crisp edges and can soften the reading of mouldings and render detail.
- Textured versions carry a coarse surface that holds soiling differently from a smooth facade coating.
- Colour and texture across a large elevation should be judged on the building, since sample panels flatter.
- The finish generally looks more uniform and more manufactured than a mineral coating, which may or may not suit.
- Once applied, changing the appearance later usually means another coating rather than removal.
Durability
Durability questions
Questions to raise rather than a service life to expect. No material has a universal lifespan — it depends on the assembly, the exposure and the upkeep.
- Is the movement causing the cracking genuinely stable, and who has confirmed that?
- What happens if a crack reopens beneath the coating, and how would anyone know?
- How will the film behave as it ages and becomes less extensible?
- Is the render behind capable of carrying this film for as long as the coating is expected to last?
Upkeep
Maintenance and repair considerations
- What are the redecoration options once this coating is on the wall, and how limited do they become?
- How would damage from impact or a service penetration be repaired without it showing?
- Is the product recorded so that a compatible material can be found later?
- If the coating blisters, what investigation happens before it is patched?
- Who is responsible for inspecting the facade and at what point in the building's cycle?
Installation
Installation dependencies
What the installation depends on — not how to do it. Method belongs to the manufacturer's instructions and the trades carrying out the work.
- Preparation, priming and application requirements are product specific and belong in the manufacturer's documentation.
- Achieving the intended film build is central to how the coating performs and is a matter of workmanship and supervision.
- Weather conditions govern application, with the acceptable range set by the product data rather than by the programme.
- Access arrangements affect continuity of work across an elevation, and a heavy film shows interruptions.
- Crack preparation and any local repair belong before the coating, not within it.
Documentation
Documentation to request
Ask for these in writing, for the specific product being proposed, and keep them with the project record.
- The manufacturer's technical data for the exact product, including its statements on movement and permeability.
- Written substrate requirements and the preparation expected over the existing surface.
- The product safety documentation covering handling, storage and disposal on site.
- A record of the product, colour and application details kept for future maintenance.
- Any survey or investigation report that explains the cracking the coating is being asked to cover.
Conversations
Questions for qualified professionals
Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.
- What is causing the cracking, and has that been investigated rather than assumed?
- Is this wall able to dry outwards, and what happens to its moisture once a heavy film is applied?
- Why this route rather than repairing the render or using a more permeable coating?
- What film build does the product require, and how will that be checked on site?
- Is the existing surface sound enough to carry the weight and adhesion of this coating?
- What are the consequences for future redecoration, and has the owner been told about them?
- How will movement joints and abutments be detailed at the coating?
- If damp appears after application, what is the diagnostic route?
Blind spots
Commonly overlooked points
- The coating conceals the crack, so the evidence a surveyor would use later disappears with it.
- Crack bridging and vapour openness pull in opposite directions, and only one of them can be prioritised on a given wall.
- Applying a heavy film to a wall with an unresolved damp source reliably makes the problem worse and more expensive.
- The decision limits future options, because removal is difficult and most later coatings must be compatible with it.
- Film build is the property that matters and is the one most easily lost to a rushed programme.
What this page does not do
- This coating is not a waterproofing system, a damp remedy or a structural repair, and must not be used as one.
- Crack bridging behaviour is a property of a specific tested product and cannot be inferred from the category.
- Whether a wall can safely carry a less permeable coating is a matter for a qualified professional who has inspected it.
- No service life, film build or performance value is stated here, because all of them depend on the product and the building.
- Composition and emissions vary widely across elastomeric coatings, and the specific product's documentation is the only reliable account of either.
Related entries
Related materials
Materials from the same family, an adjacent role in the assembly, or a shared application.
Inspiration
Related Ideas Library pages
Design directions where this material commonly appears.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this material comes up.
Go deeper
Related Build Design Hub guides
Planning guidance and neutral comparisons behind the decisions on this page.
Paints & Decorative Coatings
Reference entries for applied coatings — traditional mineral and oil paints, masonry and facade coatings, protective and marking paints, and the oils, waxes and varnishes used on timber.
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