Understand AZ100 and AZ150 roofing coating mass in Kenya, how coating weight affects corrosion resistance, and what you are actually paying for.
Coating mass is a key roofing specification that determines the amount of protective aluminium-zinc coating applied to a steel sheet. This guide explains AZ100 and AZ150 roofing coatings, what the numbers mean, how they affect corrosion protection, and what you should compare before buying roofing sheets in Kenya.
When comparing roofing sheets, many buyers focus on gauge, colour, profile and price. However, coating mass for iron sheets is another important specification because it helps indicate how much metallic protective coating has been applied to the steel.
You may encounter specifications such as AZ100 roofing and AZ150 roofing when comparing coated steel products. The numbers refer to the nominal total mass of the aluminium-zinc coating, measured in grams per square metre across both sides of the sheet. They do not refer to sheet thickness or gauge.
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Understanding these specifications can help homeowners, contractors, developers and other buyers make a more informed mabati comparison in Kenya and avoid comparing roofing products based only on appearance or price.
What Is Roofing Coating Mass?
Roofing coating mass is the total weight of the metallic protective coating applied to both sides of a steel sheet, normally expressed in grams per square metre.
For aluminium-zinc coated roofing steel, the abbreviation AZ refers to an aluminium-zinc coating system.
The number following AZ indicates the nominal total coating mass.
For example:
- AZ100 = approximately 100 g/m² total coating mass
- AZ150 = approximately 150 g/m² total coating mass
The figure represents the coating on both surfaces combined rather than the thickness of the steel itself.
This is why AZ100 and AZ150 should not be confused with:
- 100-gauge steel
- 150-gauge steel
- 1.00 mm steel
- 1.50 mm steel
They describe completely different properties.
What Does AZ150 Mean?
AZ150 means the aluminium-zinc coating has a nominal total coating mass of 150 grams per square metre across both sides of the steel sheet.
The coating consists primarily of aluminium and zinc, with the exact composition depending on the applicable product standard and manufacturer's specification.
When you see AZ150 roofing Kenya specifications, the "150" refers to coating mass, not steel thickness.
This distinction is important when comparing quotations.
A supplier could offer:
- 0.40 mm steel with AZ100 coating
- 0.40 mm steel with AZ150 coating
The steel thickness is similar, but the coating specification is different.
Therefore, asking only for "40 gauge mabati" does not provide enough information to make a technical comparison.
AZ100 vs AZ150: What Is the Difference?
AZ150 contains a higher nominal coating mass than AZ100, providing more metallic coating material for corrosion protection, although actual service life depends on the environment, product quality, installation and maintenance.
A simplified comparison looks like this:
| SpecificationAZ100AZ150 | ||
| Nominal coating mass | 100 g/m² | 150 g/m² |
| Coating material | Aluminium-zinc | Aluminium-zinc |
| Steel thickness | Separate specification | Separate specification |
| Corrosion protection | Depends on environment | Generally greater coating reserve |
| Price | May be lower | May be higher |
It is important not to conclude that AZ150 automatically guarantees 50% longer roof life.
Real-world durability depends on many factors.
These include:
- Climate
- Rainfall
- Humidity
- Salt exposure
- Industrial pollution
- Roof design
- Cutting practices
- Installation
- Fastener quality
- Maintenance
The coating specification is important, but it is only one part of the roofing system.
Why Coating Mass Matters
A protective metallic coating helps shield the underlying steel from environmental exposure, making coating mass an important consideration when selecting roofing materials.
Once exposed steel begins to corrode, the structural integrity and appearance of the roofing sheet can deteriorate.
A suitable coating helps protect the steel from:
- Moisture
- Oxygen
- Atmospheric pollutants
- Humidity
- Salt-laden air
Aluminium-zinc coatings provide corrosion protection through a combination of barrier and sacrificial protection mechanisms.
This is one reason coated steel is widely used in roofing and other outdoor construction applications.
Coating Mass Is Not the Same as Coating Thickness
Coating mass and coating thickness are related but are not interchangeable specifications.
Coating mass is normally expressed in:
grams per square metre (g/m²)
Coating thickness is expressed in:
micrometres (µm)
Manufacturers and standards commonly specify metallic coatings by mass because it provides a practical way of controlling and verifying the amount of coating applied.
Therefore, when comparing roofing products, don't assume that a higher AZ number directly represents a particular number of micrometres.
The coating's composition and density also matter.
Why Two Similar-Looking Sheets Can Have Different Specifications
Colour and profile tell you what a roofing sheet looks like, but they do not tell you the steel thickness or coating mass underneath the finish.
Two roofing sheets can have:
- The same colour
- The same profile
- Similar dimensions
- Similar surface appearance
Yet they may differ in:
- Steel grade
- Thickness
- Metallic coating
- Paint system
- Warranty
- Manufacturing specification
This is why physical appearance alone is a poor method of comparing roofing quality.
A technical datasheet is much more useful.
Does AZ150 Mean a Roof Will Never Rust?
No. AZ150 does not make a roofing sheet completely immune to corrosion; it provides a specified level of metallic coating, while the roof's environment and installation determine how that protection performs.
Corrosion can still occur if roofing sheets are:
- Incorrectly cut
- Scratched deeply
- Stored incorrectly
- Exposed to aggressive chemicals
- Installed with incompatible accessories
- Used in an unsuitable environment
Poor installation can also expose vulnerable areas of the steel.
The coating should therefore be viewed as part of a complete corrosion-protection system.
AZ Coatings for Coastal Kenya
Coating specification becomes particularly important in coastal locations because salt-laden air and high humidity can accelerate corrosion.
Areas such as:
- Mombasa
- Kilifi
- Malindi
- Lamu
- Diani
- Watamu
can expose roofing materials to marine conditions.
If you are buying roofing sheets for a coastal property, ask specifically about the manufacturer's recommended coating system and whether the product is suitable for the intended environment.
Don't simply choose a sheet because it is advertised as "Aluzinc."
Ask for the actual coating specification.
AZ100 vs AZ150 for Nairobi
In Nairobi and many inland environments, the appropriate coating specification should be selected according to the building's exposure, product specification and expected service life rather than assuming that the highest coating mass is always necessary.
For a typical residential roof, factors such as:
- Roof design
- Steel thickness
- Coating
- Paint finish
- Installation
- Maintenance
all contribute to durability.
For industrial or commercial buildings, additional environmental factors may need consideration.
Factories, chemical facilities and buildings near pollution sources may have more aggressive exposure than ordinary residential properties.
What Are You Actually Paying For?
When a higher coating mass increases the price of roofing sheets, you are paying for additional protective metallic coating material and the product specification associated with it, not simply a thicker sheet.
A roofing quotation should therefore be examined carefully.
Ask the supplier to separate the specifications:
Steel specification
- Thickness
- Steel grade
Coating specification
- Coating type
- Coating mass
Surface finish
- Paint system
- Colour
- Finish
Profile
- Corrugated
- Box profile
- IT5
- Tile profile
- Other
This gives you a meaningful comparison.
Why Sheet Thickness Still Matters
A higher coating mass does not compensate for an unsuitable steel thickness because coating and substrate perform different functions.
The steel substrate contributes to:
- Structural strength
- Stiffness
- Impact resistance
- Load performance
The metallic coating primarily contributes to:
- Corrosion protection
- Surface durability
Therefore, don't compare AZ150 and AZ100 without also checking the steel thickness.
A strong roofing specification considers both.
The Importance of Steel Grade
Steel grade is another specification that should be considered alongside thickness and coating mass because it influences the mechanical properties of the roofing sheet.
Different roofing applications may require different grades depending on:
- Profile
- Formability
- Structural requirements
- Manufacturing process
This is particularly relevant when comparing products from different manufacturers.
If two suppliers quote different prices, ask whether they are offering equivalent steel grades and coating specifications.
Coating Mass and Warranty
A roofing warranty should be examined alongside the coating specification because warranty coverage depends on the exact product, environmental conditions and stated installation requirements.
A manufacturer may specify a particular coating system for a product while also placing conditions on:
- Installation
- Storage
- Maintenance
- Fasteners
- Environmental exposure
Never assume that an AZ150 specification means an unlimited corrosion warranty.
The warranty document should be checked separately.
Proper Installation Protects the Coating
Even a high-quality coated sheet can suffer premature deterioration if installation damages the protective coating.
Common problems include:
- Scratches
- Incorrect cutting
- Metal filings left on the sheet
- Excessively tightened screws
- Incorrect handling
- Poor storage
When cutting roofing sheets, use suitable tools that minimise heat and coating damage.
After cutting, remove metallic debris from the roof surface.
Small pieces of steel left on a coated sheet can rust and create staining.
Fasteners Must Match the Roofing System
Roofing screws and accessories should be compatible with the roofing material and environmental conditions because poorly selected fasteners can become corrosion points.
Consider:
- Screw coating
- Washer quality
- Fastener material
- Coastal exposure
- Manufacturer recommendations
A premium roofing sheet paired with poor-quality fasteners is not a complete premium roofing system.
How to Compare Roofing Sheet Quotes
The easiest way to avoid paying for specifications you cannot verify is to request a written comparison showing steel thickness, coating type, coating mass, profile and warranty.
When requesting a quotation, ask for:
- Manufacturer
- Product name
- Profile
- Nominal thickness
- Steel grade
- Coating type
- Coating mass
- Paint finish
- Sheet length
- Warranty
- Recommended fasteners
This makes it easier to compare suppliers fairly.
Common Mistakes When Buying Coated Roofing Sheets
Many roofing buyers focus on gauge and colour while overlooking coating mass, steel grade, warranty conditions and environmental suitability.
Common mistakes include:
Comparing Only Price
The cheapest quotation may not contain equivalent specifications.
Comparing Gauge Without Thickness
Gauge terminology can vary, so ask for the actual nominal thickness.
Ignoring Coating Mass
A sheet's corrosion protection should be part of the specification comparison.
Choosing by Colour
Colour does not tell you the steel grade or metallic coating.
Ignoring the Environment
Coastal, industrial and humid environments can require more careful material selection.
Using Poor Fasteners
Fasteners are part of the roof system and should be suitable for the application.
What Should You Ask Your Roofing Supplier?
A professional supplier should be able to explain the technical specification rather than simply quoting a brand name and price.
Before purchasing, ask:
What is the steel thickness?
What is the steel grade?
Is the coating zinc or aluminium-zinc?
What is the coating mass?
Is it AZ100 or AZ150?
What warranty applies to this exact product?
Is the product suitable for my location?
Which fasteners should I use?
These questions can save you from making an expensive purchasing decision based on incomplete information.
Why Choose Ali Glaziers Roofing Solutions?
Ali Glaziers Roofing Solutions supplies roofing materials and accessories for residential, commercial, industrial, agricultural and institutional construction projects across Kenya.
Our team can assist with:
- Roofing sheet selection
- Gauge and thickness comparisons
- Coating specifications
- Profile selection
- Roofing accessories
- Quantity planning
- Project quotations
- Professional roofing solutions
You can browse available roofing products through our Roofing Shop.
For more information about our company and roofing services, visit Roofing About Us.
If you are unsure whether AZ100, AZ150 or another roofing specification is appropriate for your project, contact our team through Request a Quote.
Final Thoughts on AZ100 and AZ150
AZ100 and AZ150 describe coating mass, not steel thickness, and understanding the difference helps Kenyan buyers compare roofing sheets based on measurable specifications rather than appearance or price alone.
When comparing roofing sheets, look beyond:
- Colour
- Profile
- Gauge
- Price
Also check:
- Steel thickness
- Steel grade
- Coating type
- Coating mass
- Warranty
- Environmental suitability
- Fasteners
- Installation requirements
If a supplier quotes an AZ150 roofing sheet in Kenya, ask for the technical specification and warranty for the exact product. If another supplier quotes AZ100, compare the complete specification rather than assuming that one number tells you everything about roof quality.
The right roofing sheet is the one whose complete specification matches your building, environment, performance requirements and budget.
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Ali Glaziers LTD Building
Nairobi, Kenya
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+254 (0) 716 259 682
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Need help comparing roofing sheet thickness, coating mass, profiles or prices? Talk to the Ali Glaziers team before placing your order so you can choose a specification suited to your project.
