Compliance Report · Construction Materials
Roofing Sheets (Corrugated Iron / Mabati)
Where shipments fail
Ranked by how often we see it-
01 Most common
Base metal thickness (BMT) below what's advertised
Sheets sold under a heavier gauge label than their actual bare-steel thickness supports, discovered only when a buyer or inspector strips the coating and measures the base metal.
-
02 Second
Coating mass shortfall
Zinc or zinc-aluminium coating applied below the declared class (for example, a nominal Z275 sheet measuring well under 275 g/m² once acid-stripped and weighed).
-
03 Third
Profile and paint-system failure on prepainted variants
Corrugation pitch or cover width that doesn't match the declared profile, causing overlap and water-ingress problems on installation, alongside paint coatings that chalk, fade.
Applicable Standard: Regulated under the KEBS Diamond Mark of Quality scheme for coated steel sheet; hot-dip galvanized and pre-painted (Galvalume/Aluzinc) corrugated roofing sheets are assessed against the East African harmonized specifications for base metal thickness, zinc/zinc-aluminium coating mass, and paint system durability that KEBS-approved laboratories apply during inspection.
Mabati is arguably the most recognisable construction material in Kenya, manufactured locally and imported in coil form in enormous volumes — and it’s also one of the easiest categories for a buyer to be quietly shortchanged in, because the defect that matters most (base metal thickness) is specifically the dimension a “gauge” number on a price list is designed to obscure. Marketing convention describes sheets by gauge, but gauge is a coating-inclusive, imprecise proxy for the base metal thickness that actually determines structural performance and service life. A sheet can carry the gauge number of a heavier product while measuring meaningfully thinner once coating is stripped away and the bare steel is independently micrometer-tested — and that gap is where almost every dispute in this category originates. It also matters more in Kenya than in many markets because the country runs a genuinely wide range of climate exposure on a single supply chain — the same nominal product is sold for a semi-arid upcountry roof and a humid, salt-laden coastal one, and a coating shortfall that’s a minor durability discount inland can mean roof failure within two or three years on the coast.
Why This Category Gets Flagged
The dominant issue is base metal thickness (BMT) below what’s advertised — sheets sold under a heavier gauge label than their actual bare-steel thickness supports, discovered only when a buyer or inspector strips the coating and measures the base metal directly rather than trusting the total coated thickness, which is what most casual buyers and even some site supervisors actually check with a simple caliper. Second is coating mass shortfall — zinc or zinc-aluminium coating applied below the declared class (for example, a nominal Z275 sheet measuring well under 275 g/m² once acid-stripped and weighed), which shortens corrosion life dramatically and shows up first in coastal and high-humidity counties where premature rust-through becomes a warranty dispute within a few rainy seasons. Third is profile and paint-system failure on prepainted variants — corrugation pitch or cover width that doesn’t match the declared profile, causing overlap and water-ingress problems on installation, alongside paint coatings that chalk, fade, or delaminate well inside their stated warranty period. A related and increasingly common issue is coil traceability breaking down entirely between the base-steel producer and the sheet roller — a rolling mill importing coil from multiple, unlabelled sources and pressing them into a single branded product line, so that two bundles carrying identical packaging can carry meaningfully different base steel and coating quality depending on which coil happened to be on the line that week.
Test Parameters
| Parameter | Test Method / Basis | Requirement or Limit |
|---|---|---|
| Base Metal Thickness (BMT) | Micrometer measurement, coating excluded | Must meet or exceed declared nominal gauge (e.g. 0.40–0.55mm depending on gauge class) |
| Coating Mass (Zinc / Zinc-Aluminium) | Acid-stripping coating weight test | Class-dependent, e.g. Z275 (275 g/m² total both sides) or AZ150 |
| Coating Adhesion | Bend test around specified radius | No visible cracking or flaking of coating at the bend |
| Tensile Strength / Yield | Tensile test on base steel | Structural roofing grade typically ≥300 MPa yield |
| Paint Dry Film Thickness (prepainted) | Dry film thickness gauge | Typically 18–25 microns total coating system |
| Paint Adhesion / Flexibility | Cross-hatch adhesion and T-bend test | No coating loss at specified T-bend value |
| Profile Dimensions (pitch, depth, cover width) | Profile gauge / dimensional check | Must match declared profile drawing within tolerance |
Labeling Requirements
Sheets and bundles must show the manufacturer’s name and trademark, nominal gauge and base metal thickness, coating class (e.g. Z275 or AZ150), sheet length and profile type, and the KEBS Diamond Mark. Prepainted sheets must additionally show the paint system and any stated corrosion or colour-fade warranty class, since a warranty claim without this baseline documentation is effectively unenforceable. Imported coil consignments must carry country of origin and importer details consistent with the accompanying Certificate of Conformity.
Packaging & Documentation
| Document | Purpose / When Required |
|---|---|
| Certificate of Conformity | Required for imported coil or finished sheet consignments prior to shipment |
| KEBS Diamond Mark License | Confirms ongoing factory-level compliance for local mabati manufacturers |
| Mill Test Certificate (base coil) | Confirms base steel grade and coating mass from the originating coil supplier |
| Coating/Paint System Warranty Documentation | Substantiates any stated corrosion or paint-fade warranty period |
| Bundle Count & Length Certificate | Confirms actual sheet count and length matches invoiced quantity |
Typical Gaps We Find
Base metal thickness shortfall is the defect we find most consistently — a sheet sold under a heavier gauge label than its actual bare-steel thickness once independently stripped and measured, which is precisely the kind of shortfall a buyer has no practical way to detect on a stacked pallet at a hardware depot. Coating mass below the declared class on shipments destined for coastal or high-rainfall counties is a close second, and it’s the one that turns into the most expensive dispute, because premature rust-through often isn’t visible until well after installation and roofing has been fixed in place. We also regularly find bundles arriving with no mill test certificate linking the finished sheet back to its base coil at all — meaning there’s no way to verify any of the above without independent destructive testing. Profile and sheet-count shortfalls are a smaller but persistent complaint too, where a bundle invoiced for a specific number of full-length sheets arrives with a mix of lengths or a lower actual count, a discrepancy that’s easy to miss on a busy site delivery but adds up quickly across a full roofing order. None of this requires a different manufacturing process — it requires the base-coil and coating documentation to travel with the finished sheet, which is exactly the gap this assessment is built to close before the sheets are ordered rather than after they’re already on a roof.