On-Site Spraying & Application

On-Site Spraying: The Complete Guide

Q: What surfaces can be sprayed on-site?

On-site spraying can be applied to a wide range of commercial surfaces including aluminium window frames and curtain walling, steel and aluminium shopfronts, roller shutter doors, cladding panels, signage and fascias, ceiling soffits and suspended ceilings, lift doors, staircases and balustrades, powder-coated metalwork, and interior surfaces. Almost any surface that accepts a liquid coating can be treated on-site, the key requirement is that the surface can be properly prepared and that adjacent areas can be adequately masked to contain overspray.

Q: How long does on-site spraying take?

Project duration varies significantly based on surface area, accessibility, coating system, and site complexity. A single shopfront spraying project might take one to two days; a full exterior aluminium window recoating programme on a multi-storey commercial building might take one to three weeks. A meaningful portion of total project time is spent on surface preparation and masking, typically 30–50% of the working time, as these stages determine the quality and longevity of the finished result.

Q: What preparation is required before on-site spraying?

Surface preparation is the most critical stage of any on-site spraying project and directly determines the adhesion, durability, and appearance of the finished coating. At minimum, all surfaces must be thoroughly cleaned to remove dust, grease, and contaminants. Corroded areas are mechanically abraded or treated with appropriate products. Existing coatings are assessed, if poorly adhering, they are stripped back to the substrate. Aluminium and non-ferrous metals receive etch primer before the finish coat system. All bare metal receives an appropriate primer coat. The surface must be dry, within the required temperature and humidity range, and free from condensation before any coating is applied.

Everything you need to know about professional commercial on-site paint spraying, surface preparation, masking, equipment selection, coating systems, safety requirements, and quality control, from a contractor with 29 years of on-site experience.

Anthony Jones, Vanda Coatings Updated February 2026 12 min read On-Site Spraying Surface Preparation Technical Guide

On-site spraying is the application of liquid decorative and protective coatings to surfaces in their installed position, on the building or structure, rather than in a factory or workshop. It is the method that allows a commercial building's aluminium windows, shopfront, cladding panels, roller shutters, and interior ceiling to be transformed with a fresh, durable finish without any component needing to be removed, replaced, or sent offsite.

Done well, on-site spraying produces results that are indistinguishable from a factory-applied finish. Done poorly, with inadequate preparation, incorrect coating selection, or insufficient masking, it leaves a result that fails early and costs far more to correct than it would have cost to do correctly in the first place.

This guide covers every stage of a professional on-site spraying project in sequence. It is written for facilities managers, building owners, contractors, and specifiers who want to understand what a high quality on-site coating programme involves, and what to look for when assessing a contractor's approach.

1. What is on-site spraying and when is it the right solution?

On-site spraying is not simply "painting with a spray gun". It is a structured, sequenced process, starting with a survey of the existing surface condition and ending with a quality-checked finished coating, that uses professional spray equipment, specialist coating systems, and trained operatives to deliver a result that brushes and rollers cannot produce on commercial metalwork at scale.

The conditions that make on-site spraying the right solution are:

The substrate is structurally sound, the underlying surface is solid and capable of accepting a new coating without the new coating simply replicating the defects beneath it
The existing coating is adhering adequately, or can be fully stripped back to bare metal where it is not
Adjacent areas can be adequately masked, so that overspray is contained and there is no risk of coating contamination on surfaces, glazing, or goods that must remain uncoated
Environmental conditions are within range, temperature, humidity, and wind speed are within the coating manufacturer's specified application window
Replacement is not more cost effective, for heavily corroded or structurally compromised surfaces, full replacement may be more practical than recoating

When these conditions are met, on-site spraying consistently delivers a result that is faster, less disruptive, and significantly cheaper than like-for-like replacement, typically at 20–40% of the cost for aluminium window or shopfront systems.

20–40%

of replacement cost, typical budget saving when recoating vs replacing aluminium windows

10–15

years, typical service life of a professionally applied 2K acrylic coating system

30–50%

of total project time is typically spent on preparation and masking, the stages that determine the result

years of on-site commercial spraying experience behind every Vanda Coatings project

2. The three spray methods used in commercial on-site work

Professional on-site contractors use three distinct application methods, each suited to different surface types and project conditions. Selecting the correct method for each project, and sometimes for each element within a project, is one of the key technical decisions that determines outcome quality.

Airless Spraying

Uses high hydraulic pressure, typically 1,000–3,000 psi for commercial coatings, to atomise paint through a nozzle tip without introducing compressed air into the fluid stream. The fastest application method for large flat or profiled surfaces: cladding panels, suspended ceilings, large window arrays, and warehouse interiors. Applies approximately four times faster than brush application on large surface areas. Requires thorough masking due to 20–40% overspray. The standard method for high-output commercial coating work.

HVLP Spraying

High Volume Low Pressure, uses a high volume of compressed air at low pressure (typically 0.5–1.0 bar at the cap) to atomise the coating. Produces finer atomisation and significantly less overspray than airless, with transfer efficiency of 65–90%. Preferred for detailed architectural metalwork, shopfronts, door frames, and interior work where precision matters and overspray control is critical. The method of choice for close-in work on occupied commercial sites where containment planning is paramount.

Electrostatic Spraying

Applies an electrical charge to atomised coating droplets, which are then strongly attracted to the earthed metal surface. This wrap-around effect dramatically reduces overspray, improves coverage on complex three-dimensional shapes, and increases transfer efficiency to 90% or more. Particularly effective on railings, gates, balustrades, ornamental metalwork, lift doors, and office furniture where complex geometry makes conventional spraying wasteful and difficult to control uniformly.

3. Stage 1. Pre-project survey and specification

Every professional on-site spraying project begins with a survey, not an estimate written from a photograph. A proper pre-project survey involves a trained estimator or contracts manager physically inspecting the surfaces to be coated, assessing the existing coating condition, identifying any areas of corrosion, damage, or adhesion failure, and establishing what preparation work will be required before any coating can be applied.

The survey output determines the project specification: which coating system is appropriate, how many coats are required to reach the specified dry film thickness, what preparation method is needed, and whether any remedial structural or repair work is needed before coating commences. Without a proper survey, any quotation is based on assumptions that may prove incorrect once work begins, leading to cost overruns, programme delays, or a compromised result.

What a survey should establish

The existing substrate material, aluminium, mild steel, galvanised steel, UPVC, concrete, or composite
The existing coating type and condition, adhering soundly, flaking, chalking, peeling, or degraded
The presence and extent of any corrosion, particularly on steel and galvanised substrates
Access requirements, can work be done from ladders, or is scaffold, MEWP, or rope access required?
Site constraints, occupied or unoccupied, hours restrictions, proximity of sensitive areas requiring enhanced masking
Environmental exposure classification, south-facing, coastal, industrial, or sheltered urban? Exposure class determines coating specification and film thickness targets

4. Stage 2. Surface preparation

Surface preparation is the single most important stage of any on-site spraying project. It determines adhesion, and adhesion determines durability. The highest-quality coating system applied over inadequate preparation will fail prematurely, often within months, whereas good preparation with a standard coating system will significantly outlast poor preparation with a premium one.

The sequence of preparation steps varies by substrate and existing coating condition, but the general framework is as follows:

Cleaning, remove all surface contamination

Every substrate must be thoroughly cleaned before any mechanical preparation or coating begins. Cleaning removes traffic film, atmospheric grease, oils, bird deposits, salt deposits, and other contaminants that would prevent adhesion. Professional cleaning uses a specialist industrial degreaser applied by wet cloth or sponge, working from top to bottom, followed by a clean water wipe-down. High-pressure washing is appropriate for large exterior surfaces such as cladding and roof systems. Surfaces must be fully dry before the next stage, applying coating over damp or wet surfaces is a common cause of early adhesion failure.

Existing coating assessment and strip-back

The existing coating is assessed by adhesion testing, typically by cross-cut tape test (ISO 2409) or knife test, to determine whether it provides a sound base for overcoating. Coatings that are firmly adhering throughout can be overcoated after scuff-sanding. Coatings that are locally flaking, heavily chalked, or showing widespread adhesion failure must be mechanically stripped back to bare substrate in the affected areas, or in full if the failure is widespread. Partial strip-back requires careful feathering of the edges of remaining intact coating to prevent an edge read-through in the finished surface.

Corrosion treatment, ferrous and non-ferrous substrates

Any visible surface rust on mild steel or galvanised steel substrates must be mechanically abraded using wire cups, grinding discs, or needle guns to remove loose corrosion products back to bright metal or to a surface preparation grade appropriate for the specified primer system, typically ST2 or ST3 to ISO 8501-1. Residual tight rust that cannot be fully removed mechanically can be treated with a penetrating rust converter as a supplementary measure, but this is not a substitute for mechanical preparation of loose or active corrosion. On aluminium, surface oxide is addressed chemically through etch priming rather than by heavy mechanical abrasion.

Abrasion, mechanical keying of the surface

All surfaces to be coated, whether bare substrate or intact existing coating, must be mechanically abraded to provide a key for the new coating. For aluminium and existing painted surfaces, this typically means scuff-sanding with P180–P240 grit to scratch the surface and increase mechanical adhesion. For bare steel, abrasive blasting or needle gunning achieves the required surface profile. After mechanical abrasion, all dust and swarf must be removed by vacuum or tack cloth before coating commences, abrasion debris left on the surface causes inclusion defects in the finished film.

Etch priming of bare aluminium and non-ferrous metals

Bare aluminium, whether newly exposed by strip-back or as part of a new installation, requires an etch primer before any finish coat is applied. Etch primer contains a mild acid that reacts chemically with the aluminium oxide layer, creating a chemically bonded conversion coating that provides significantly superior adhesion compared to a conventional primer applied over clean bare aluminium. Etch primer must be applied to a freshly prepared, clean, and dry surface, and the finish coat system must follow within the overcoating window specified by the manufacturer, typically 2–24 hours at 20°C.

Final inspection before coating

Before any coating is applied, the prepared surface receives a final visual inspection, checking for missed areas of contamination or corrosion, incomplete abrasion, dust, or areas where the preparation has been compromised by subsequent handling. Any deficiencies are addressed at this stage. Temperature, humidity, and dew point are checked to confirm that environmental conditions are within the coating manufacturer's specified application window, typically above 10°C substrate temperature, below 85% relative humidity, and at least 3°C above the dew point to prevent moisture condensation on the surface during application.

5. Stage 3. Masking

Masking is the process of protecting all surfaces adjacent to the work area from overspray, atomised paint particles that miss the target surface and settle on whatever is nearby. On commercial on-site spraying projects, masking is not optional. It is a critical part of the job, and the time and care taken with it directly determines whether the project outcome is professional or damaging.

Inadequate masking on a commercial site can coat glazing, vehicle finishes, neighbouring shopfronts, signage, HVAC equipment, or the belongings of building occupants. The consequential costs of cleaning or replacing contaminated items can far exceed the value of the original spraying contract.

What needs to be masked

All glazing adjacent to spray areas, glass is particularly susceptible to fine overspray particles, which can be very difficult to remove once dry without risking scratching
All hardware and fixings not being coated, handles, hinges, locks, letter plates, drainage channels
Surrounding brickwork, render, and stonework, particularly important on shopfront and cladding projects where substrate colours differ significantly from the new coating colour
Adjacent vehicles and street furniture, especially on pavement-level shopfront spraying projects where passing traffic may be affected
Internal surfaces and contents, on interior spraying projects, all furniture, floors, and equipment must be covered with polythene sheeting

Masking materials used professionally on-site

Masking tape, used to secure masking paper and polythene to surfaces and to create precise edges at coating boundaries; low-tack tape is used on delicate surfaces to prevent substrate damage on removal
Masking paper, for straight-edged masking of reveals, soffits, and defined areas adjacent to the work zone
Polythene sheeting, for large-area protection of glazing, floor areas, vehicles, and equipment
Fine mist barriers, on outdoor projects with any wind risk, fine-mesh fabric overspray barriers can be erected as a secondary containment measure around the perimeter of the work zone

Masking is not a stage to cut short. On a typical shopfront or aluminium window recoating project, masking time accounts for 25–40% of total on-site labour time. A contractor who produces an unusually low quotation has almost certainly reduced the masking allowance, and the consequences of that will be visible on the day their operatives start spraying.

6. Stage 4. Coating system application

With preparation complete and masking in place, coating application proceeds in the specified sequence. For commercial metalwork, aluminium windows, shopfronts, steel cladding, the standard system is a two-coat or three-coat 2K acrylic urethane system applied by airless or HVLP spray. Each coat is applied to the manufacturer's specified wet film thickness, allowed to reach the minimum overcoat condition (verified by dry film thickness measurement), and then the next coat is applied.

Standard coating sequence for aluminium metalwork

Etch primer coat

Applied to all bare or newly exposed aluminium at 15–20 microns dry film thickness. The etch primer creates the chemical bond between the aluminium substrate and the subsequent coating system. It must be applied within the manufacturer's stated pot life after mixing, and the subsequent coat must follow within the stated overcoating window, typically 2–24 hours at 20°C, shortening in colder conditions.

First finish coat

The two-component acrylic finish coat is mixed in the correct ratio, base coat and hardener, at the point of use. The pot life of a mixed 2K acrylic is typically 4–6 hours at 20°C, so only as much coating as can be applied within that window should be mixed at any one time. The first finish coat is applied to a dry film thickness of 35–40 microns, building the coating film and sealing the primed substrate. Any holidays, pinholes, or thin areas identified after this coat must be addressed before applying the second coat.

Second finish coat

Applied after the first coat has reached the minimum overcoat condition, typically a minimum of 2–4 hours at 20°C. The second finish coat brings the total dry film thickness of the finish system to 70–80 microns. It provides the final colour and gloss level, and fully seals any minor imperfections from the first coat. On high-exposure applications, coastal, industrial, or south-facing elevations, a third coat may be specified to achieve additional film build and UV protection.

Dry film thickness verification

After each coat, dry film thickness readings are taken at multiple points across the coated surface using a calibrated elcometer. Readings confirm that the specified film thickness has been achieved consistently across the surface. Areas that read below specification are identified and receive an additional pass before the next coat is applied. This stage is non-negotiable on a properly specified commercial coating project, applied film thickness is the primary predictor of coating longevity, and no coating system can be relied upon to perform to its rated service life at under-thickness.

Masking removal and reinstatement

Masking is removed carefully after the final coat has achieved sufficient surface hardness, typically 1–2 hours after application at 20°C. Tape is removed at an angle away from the coating edge to avoid lifting the fresh film. Any minor edge bleed is addressed with a fine artist's brush or cotton bud before the coating fully hardens. All masking materials are collected and removed from site in accordance with waste disposal regulations.

7. Coating systems for common commercial substrates

The correct coating system is determined by the substrate, the existing coating type, the exposure classification, and the required service life. The following table summarises the standard systems used by professional on-site contractors across the most common commercial surfaces.

Substrate	Typical System	No. of Coats	Expected Service Life
Aluminium windows & curtain walling	Etch primer + 2K acrylic	2–3 coats	10–15 years
Steel shopfront & frames	Zinc phosphate primer + 2K acrylic	2–3 coats	8–12 years
Galvanised steel cladding	T-wash + epoxy primer + 2K acrylic	3–4 coats	10–15 years
Powder-coated aluminium	Etch primer + 2K acrylic	2 coats	8–12 years
Roller shutter doors (steel)	Zinc phosphate primer + 2K acrylic	2–3 coats	8–10 years
Interior ceiling soffits	Stain-block primer + specialist ceiling coat	2 coats	5–10 years
Exposed structural steelwork	Zinc phosphate primer + 2K epoxy + polyurethane finish	3–4 coats	15+ years

8. Safety requirements for on-site spraying

On-site paint spraying presents specific health and safety risks that must be managed through documented risk assessment and safe working procedures. Professional on-site contractors carry COSHH assessments, RAMS (Risk Assessment and Method Statements), and product data sheets for every coating used on site, and these must be available to the principal contractor or site manager on request.

PPE is mandatory during coating application, not optional. The primary respiratory risk during on-site spraying is inhalation of atomised coating droplets and solvent vapour. Operatives must wear a correctly fitted, approved respirator during all spray application, dust masks provide no protection against solvent vapour or aerosol particles. Eye protection, full overalls, and chemical-resistant gloves are required throughout application. On occupied sites, operatives must ensure that building users are not exposed to spray mist or solvent odour without adequate ventilation.

Key safety requirements for commercial on-site spraying

COSHH assessment, a completed COSHH (Control of Substances Hazardous to Health) assessment for each coating material used on site must be available and understood by all operatives before work commences
Respiratory protection, air-fed or appropriate cartridge-type respirator matched to the solvent and vapour profile of the coating in use
Ventilation, adequate airflow through the work area to prevent accumulation of solvent vapour; particularly critical in enclosed interiors and basement-level work areas
Access equipment certification, operatives using mobile elevated work platforms (MEWPs) must hold IPAF cards; those using scaffold towers must hold PASMA certification
Airless spray gun safety, trigger safety lock must be engaged whenever the gun is not in active use; pressure must be fully relieved before changing tips or performing any maintenance on the gun or hose
Exclusion zones, clearly marked barriers and signage to prevent building users or members of the public from entering the spray zone during application
Fire risk management, solvent-borne coatings and thinners are flammable; no ignition sources within the work area; suitable fire extinguisher present at all times during application
Waste disposal, all solvent-contaminated materials, empty containers, and masking waste must be collected and disposed of in accordance with hazardous waste regulations

9. Quality control and inspection

Quality control on an on-site spraying project does not happen only at the end, it is built into every stage of the process. A professional contractor establishes inspection checkpoints at each stage, rather than relying on a single visual check at the end.

Quality control checkpoints throughout the process

Before preparation begins: condition survey documented, specification confirmed, environmental conditions checked, temperature, humidity, dew point
After cleaning: visual check for residual contamination; substrate confirmed dry and free from moisture
After abrasion: visual check for complete mechanical keying throughout; dust removed; no bare metal areas missed
Before first coat: environmental conditions re-checked; substrate temperature confirmed above minimum; coating mixed in correct ratio and within pot life
After each coat: dry film thickness readings at minimum three points per square metre; any areas below specification re-coated before proceeding to the next coat
After masking removal: edges inspected for bleed or lifting; touch-in work completed before coating reaches full hardness
Final inspection: full visual inspection in good light for runs, sags, holidays, pinholes, contamination, or inconsistent sheen; client or client representative inspection and sign-off

At Vanda Coatings, every project is managed by an experienced contracts manager who coordinates preparation, coating application, and site safety from initial survey through to client sign-off. We do not subcontract our operative teams, all on-site spraying is carried out by our own directly employed, trained operatives. We have been operating this way since 1997, and our commitment to quality control is the reason our aluminium window recoating work carries a 10-year guarantee.

10. Common on-site spraying project types

On-site spraying is applied across a wide range of commercial project categories. The application method, coating system, and preparation approach varies by surface type, but the underlying quality principles remain constant across all of them.

Aluminium window and curtain walling recoating, the largest single category of on-site spraying by volume; typically involves etch priming and 2K acrylic application to existing powder-coated or factory-finished aluminium frames, either as a colour change or a condition restoration programme
Shopfront and entrance frame spraying, often combined with signage refreshes and rebrand programmes; high-visibility work requiring precision masking and a factory-quality finish that reflects on the building occupant's brand
Roller shutter door spraying, particularly common on retail parks and industrial estates where the visual appearance of security shutters affects overall site presentation; often a colour-change requirement to align with updated branding
Cladding and rainscreen panel painting, large surface areas suited to airless application; preparation requirements vary significantly based on panel material and the condition of the existing coating system
Ceiling void spraying, suspended ceilings and exposed soffit systems in retail, industrial, and office environments; HVLP application with specialist ceiling coatings designed for irregular, hard-to-reach surfaces
Electrostatic metalwork, railings, balustrades, lift doors, complex three-dimensional metalwork where the wrap-around effect of electrostatic application provides superior coverage efficiency and significantly reduced overspray compared to conventional spray methods
Car showroom recoating, full interior and exterior colour transformation of automotive retail environments, often on tight timescales to minimise showroom closure periods

Frequently asked questions

Q What is on-site paint spraying?

On-site paint spraying is the application of liquid decorative or protective coatings to surfaces in their installed position, on the building or structure, using professional spray equipment. It allows surfaces such as aluminium windows, shopfronts, cladding, and roller shutters to be transformed with a new, durable coating finish without the surfaces being removed or replaced. The process includes surface preparation, masking of adjacent areas, and multi-coat application to achieve a factory-quality result on site.

Q What surfaces can be sprayed on-site?

On-site spraying can be applied to aluminium window frames and curtain walling, steel and aluminium shopfronts, roller shutter doors, cladding panels, signage and fascias, ceiling soffits, suspended ceilings, lift doors, staircases and balustrades, powder-coated metalwork, and interior surfaces. Almost any surface that accepts a liquid coating can be treated on-site, the key requirements are that the surface can be properly prepared and that adjacent areas can be adequately masked to contain overspray.

Q How long does on-site spraying take?

Project duration varies by surface area, accessibility, coating system, and site complexity. A shopfront spraying project typically takes one to two days. A full exterior aluminium window recoating programme on a multi-storey building might take one to three weeks. A meaningful proportion of total project time, typically 30–50%, is spent on surface preparation and masking, as these stages determine the quality and longevity of the finished result.

Q Does on-site spraying cause disruption?

Professionally managed on-site spraying is designed to minimise disruption. Work is scheduled around business operations, often out of hours or in phases to keep areas accessible. Masking protects all surrounding surfaces and building contents from overspray. Modern water-based 2K acrylic coating systems have low odour and low VOC content, making them suitable for occupied environments. The main variables affecting disruption are access requirements, ventilation needs, and whether the work must be undertaken during or outside business hours.

Q What is the difference between airless, HVLP, and electrostatic spraying?

Airless spraying uses high hydraulic pressure to atomise coating without compressed air, it is the fastest method and suits large flat or profiled areas such as cladding and ceilings. HVLP uses a high volume of low-pressure compressed air, it produces a finer finish with less overspray and is preferred for detailed metalwork and occupied sites where containment is critical. Electrostatic spraying adds an electrical charge to the coating droplets so they are attracted to the earthed metal surface, this reduces overspray dramatically, improves wrap-around coverage on complex shapes, and is particularly effective on railings, gates, balustrades, and lift doors.

Q What preparation is required before on-site spraying?

Surface preparation is the most critical stage and directly determines adhesion and longevity. At minimum, surfaces must be thoroughly degreased and cleaned. Corroded areas are mechanically abraded to remove loose rust. Existing coatings are assessed, if poorly adhering, they are stripped back to bare substrate. Aluminium and non-ferrous metals receive etch primer before the finish system is applied. The surface must be dry, within the manufacturer's required temperature and humidity range, and free from condensation before any coating is applied.

Q How long does on-site sprayed coating last?

A professionally applied 2K acrylic system on properly prepared aluminium or steel will typically last 10–15 years before requiring attention, depending on the coating specification, exposure level, and maintenance regime. Vanda Coatings provides a 10-year guarantee on aluminium window recoating projects carried out to the full specification. The key factors affecting longevity are the quality of surface preparation, the coating system chosen, the number of coats applied to the specified dry film thickness, and the exposure conditions the coated surface faces.

Anthony Jones

Director, Vanda Coatings, 29 years experience

Anthony has managed on-site commercial spraying projects across the UK since the late 1990s, from single shopfront resprays to multi-building aluminium window programmes on large commercial estates. He oversees specification, contracts management, and quality control at Vanda Coatings, and writes these technical guides to help facilities managers, building owners, and contractors understand what professional on-site coating work involves, and what distinguishes a quality contractor from one who will cut corners.