For poultry or livestock sheds with constant ammonia and moisture, the PPGI coil specification that usually works best is a galvanized substrate with a heavier zinc coating, a primer plus topcoat system selected for chemical and humidity resistance, and a back coating — not bare or thin wash-coated reverse — plus fixings and laps detailed so that ammonia-laden air and wash water cannot sit against cut edges. The exact coating type, film thickness and substrate class should be agreed in writing against the shed environment, because no single paint system suits every farm building. This article explains how farm cladding differs from standard industrial cladding, and how to translate those differences into a coil specification and a request for quotation.
Why livestock buildings are a harsher environment than most industrial sheds
Standard industrial cladding is usually asked to resist rain, sun and moderate pollution. A livestock building adds a chemical load and a maintenance pattern that the same coil may not have been specified for.
Ammonia vapour
Ammonia is released continuously from manure and litter, and its concentration rises where ventilation is poor or where stock density is high. In humid air, ammonia is aggressive to many metals and to some paint chemistries. It also tends to concentrate under the roof, at the ridge and at the top of walls — exactly where cladding is least accessible for inspection.
Moisture and condensation
Warm, moist air meeting a cooler sheet underside creates condensation. On the inside face, that water can remain in contact with the coating for long periods. Where the reverse side is only a thin wash coat, the barrier is minimal.
Dust, litter and biofilm
Dust, feed particles and litter adhere to surfaces, hold moisture and can create localised aggressive conditions. Dirt retention matters as much as the paint chemistry itself.
Washing and disinfection
Between flocks or batches, buildings are often washed, sometimes with detergents or disinfectants. The cladding and, more importantly, the fixings and cut edges may be exposed to water at pressure and to cleaning chemicals not considered in a standard industrial specification.
Mechanical knocks
Cladding in farm buildings is exposed to equipment, gates, loading, birds and livestock, and to foot traffic during cleaning. Impact and abrasion damage create small breaks in the coating that become corrosion initiation points.
How farm cladding specification should differ from standard industrial cladding
The table below is general technical guidance, not a fixed recipe. Final values should be confirmed by the coil supplier and, where relevant, by the paint supplier’s data sheet for the specific product.
| Element | Typical standard industrial cladding approach | Farm/livestock adjustment to discuss | Why it matters |
|---|---|---|---|
| Substrate | Hot-dip galvanized steel, commonly Z100–Z180 class | Consider a heavier zinc coating class (for example Z180–Z275) where the building is humid or ammonia load is high | Zinc is the last barrier at scratches and cut edges; more of it buys more tolerance |
| Pre-treatment | Standard conversion coating | Confirm the pre-treatment suits the chosen paint system and substrate | Adhesion and corrosion resistance start at the interface |
| Primer | Standard primer, often thin | Discuss a primer with good barrier and chemical resistance, at an agreed film build | Primer is the main barrier if the topcoat is damaged |
| Topcoat chemistry | Polyester or silicon-modified polyester | Consider polyurethane, HDP or PVDF where chemical and humidity resistance matter more than cost | Chemistries differ in resistance to ammonia, moisture and cleaning agents |
| Topcoat thickness | Often around 20 µm nominal | Discuss a higher build, for example 25 µm or more, subject to supplier confirmation | More film thickness gives more abrasion and chemical margin |
| Back coating | Thin wash coat or none | Specify a proper back coating with agreed thickness | The interior face sees the ammonia and condensation first |
| Cut edges and fixings | Standard fasteners, edges often unsealed | Specify compatible coated or stainless fasteners, sealed laps, and edge treatment where accessible | Most corrosion starts at edges, holes and fixings |
| Profile and drainage | Standard trapezoidal or corrugated | Choose a profile that drains and sheds dirt, and detail the ridge and eaves to avoid traps | Standing water and dirt are the enemy |
Where a project references a standard — for example a prepainted steel product standard or a galvanized substrate standard — confirm the required edition and the exact contract values with the buyer, the designer and the supplier. Standards set frameworks; they do not by themselves guarantee performance in a specific barn.
Substrate and metallic coating: the part most buyers under-specify
Paint protects the surface, but the substrate and its zinc coating determine what happens when the paint is damaged. In farm buildings, damage is likely: fixings, knocks, cutting on site and abrasion during cleaning.
Zinc coating mass
Hot-dip galvanized substrate is the normal base for PPGI coil. Zinc coating mass is usually expressed in g/m² total both sides, or as a Z-class. Higher zinc mass generally means more sacrificial protection at scratches, but it also affects cost and forming behaviour. Buyers should ask for the zinc coating mass to be stated on the certificate and in the contract, not just the class name.
Steel grade and thickness
Roof and wall sheets need enough stiffness to span purlins and resist wind and impact, and enough ductility for the roll forming and bending the project requires. Specify yield strength, tensile strength and elongation where the profile or span demands it, and confirm the grade is suitable for the forming route. If a project is comparing substrates, the GI coil page explains the galvanized base in more detail.
Surface quality
Surface defects under the paint can become corrosion initiation points. Ask how surface quality is defined and inspected, and whether the coil is supplied with a mill or supplier inspection certificate.
Paint system selection: chemistry, thickness and back coating
Paint system choice is the decision with the largest effect on farm performance, and the one most often reduced to a single word on a purchase order.
Topcoat chemistry
Polyester systems are widely used and cost-effective for general cladding. Where chemical resistance and humidity resistance are priorities — as in livestock buildings — polyurethane, high-durability polyester (HDP) or PVDF systems are often discussed. Each has trade-offs in cost, colour range, forming behaviour and repair. Ask the paint supplier, through the coil supplier, for the data sheet relevant to the specific product and the intended environment.
Film thickness
Nominal topcoat and primer thicknesses should be stated in the contract, together with the tolerance and the test method used to verify them. Thicker is not automatically better if the system is not designed as a whole, but a thin system leaves little margin for abrasion.
Back coating
This is where farm specifications most often fall short. The interior face of a livestock shed roof is exposed to ammonia and condensation. A proper back coating, at an agreed thickness, provides a barrier that a wash coat does not. Where the building is washed down, consider whether the back coating also needs resistance to the cleaning agents used.
Colour and gloss
Light colours reduce solar heat gain, which can matter for stock comfort. Gloss affects dirt retention and appearance; a slightly lower gloss may hide marking, but dirt shedding depends on the chemistry as well. Colour fastness and chalking behaviour should be confirmed for the chosen system.
Fixings, laps and detailing: where farm cladding usually fails first
Most early corrosion on farm cladding is found at cut edges, drilled holes, fixings and laps — not in the middle of a painted pan. Specification should cover these details as explicitly as the coil.
- Fasteners: use fasteners with a coating system compatible with the sheet and adequate for the environment; discuss stainless or heavily coated options for high-humidity or high-ammonia zones.
- Cut edges: minimise exposed cut edges, orient laps to shed water, and consider edge sealing or touch-up where the design allows and the supplier’s system permits.
- Laps: follow the profile manufacturer’s lap and fixing recommendations, and avoid details that trap water or litter.
- Ridge and eaves: ventilate and detail so that ammonia-rich moist air does not stagnate against the underside.
- Contact with other materials: avoid direct contact between the coated steel and untreated timber, cement or dissimilar metals where galvanic or chemical interaction is possible; use compatible separators.
- Handling and site storage: store coils and sheets off the ground, under cover, with ventilation; avoid condensation between sheets.
Forming also matters. Roll forming and bending stress the coating, especially at tight radii. Confirm the minimum bend radius and forming recommendations for the specific paint system, and discuss whether the coil is supplied with a protective film if the sheets will be handled heavily on site.
Practical RFQ checklist for farm and livestock cladding
Use this list to turn a farm building brief into a comparable quotation request. Add project-specific items as needed.
- Building type, location and climate, including whether the site is coastal or industrial.
- Application: roof, wall or both; interior and exterior exposure.
- Stock type and expected ammonia and humidity conditions, including washing and disinfection regime.
- Substrate: steel grade, thickness and tolerance.
- Metallic coating: zinc coating mass or Z-class, stated as a number.
- Paint system: primer chemistry and thickness; topcoat chemistry and thickness; back coating chemistry and thickness.
- Colour, gloss and any colour-matching requirement.
- Coil dimensions: width, inner diameter, coil weight range.
- Mechanical properties required for the forming route.
- Surface quality and inspection requirements.
- Documentation: inspection certificate, test reports and declaration of conformity as applicable.
- Packaging, marking and shipping terms.
- Quantity, delivery schedule and any phased delivery requirement.
- Standards referenced, with the edition and the exact values required.
- Warranty terms offered by the supplier, and the conditions attached to them.
Common mistakes buyers make
- Specifying “PPGI” without a paint system. The word covers many combinations of substrate, primer, topcoat and back coating.
- Ignoring the back coating. The interior face is often the first to fail in livestock buildings.
- Buying on price per tonne alone. Cost drivers include substrate grade, zinc coating mass, paint chemistry, film thickness, colour and coil size. A lower price often reflects a lighter specification. Ask for a dated quotation that states the full specification, and compare like with like.
- Treating the standard as the specification. A standard reference does not fix the values; the contract does.
- Under-specifying fixings. The best coil will still fail at a mismatched fastener.
- Assuming a service life. Any expected life depends on substrate, metallic coating, paint system, environment, forming, installation and maintenance. Ask suppliers to state the basis of any performance claim rather than a single number.
- Poor site storage. Condensation and mechanical damage during storage can undo a good specification.
Frequently asked questions
What PPGI specification is best for a poultry shed?
There is no universal answer. A common starting point for discussion is a galvanized substrate with a heavier zinc coating, a primer and topcoat system chosen for chemical and humidity resistance, and a proper back coating. The exact chemistry and thicknesses should be agreed with the coil and paint suppliers against the specific building, ventilation and washing regime.
Is polyester suitable for livestock buildings?
Polyester is widely used for general cladding and may be adequate in well-ventilated, low-humidity buildings with good detailing. Where ammonia, moisture or washing chemical exposure is significant, buyers often discuss polyurethane, HDP or PVDF systems. Confirm suitability with the paint supplier’s data for the specific product.
Does a thicker coating always last longer?
Not automatically. Performance depends on the whole system — substrate, pre-treatment, primer, topcoat, back coating, forming and detailing — and on the environment and maintenance. Thickness is one variable, not a guarantee.
How should cut edges and fixings be handled?
Minimise exposed edges, orient laps to drain, use fasteners with a compatible and adequate coating, and follow the profile manufacturer’s fixing recommendations. Where touch-up is permitted by the supplier, use the recommended product.
Can one coil be used for both roof and walls?
Often yes, but the roof sees more rain, sun and condensation and the walls see more knocks and washing. Check whether the same paint system and thickness are appropriate for both, or whether the roof should have a higher specification.
How do I compare quotations fairly?
Ask every supplier to quote against the same written specification, including zinc coating mass, paint chemistry, film thicknesses, back coating, steel grade and tolerances. Request a dated quotation and the supporting test documentation, then compare the specifications before comparing prices.
Next step
If you are specifying coil for a poultry, pig or dairy building, the most useful next step is to write the environment and the required specification into a single document and send it out for quotation. ChinaCNU Steel can respond to a structured RFQ covering substrate, metallic coating, paint system, back coating, dimensions and documentation. Start with the PPGI coil page for product context, and send your specification through the contact page to request a dated quotation. Including the building type, ventilation and washing regime in your enquiry helps ensure the reply addresses the conditions your cladding will actually face.
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