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Pavers, Slabs, and Outdoor Porcelain: Understanding the Real Differences in Paving Elements Author: Stefan Poirier | Technical Advisor & National Trainer at ROMEX HardscapesCMHA/PICP Specialist | CPI / SRW / ASTMc1781 Qualified In hardscaping, the words pavers, slabs, and porcelain are often used like they mean the same thing. They do not.That mix-up causes real problems on jobsites and in specifications. A surface may look great on day one, but if the paving unit was treated like the wrong category, the result can be shifting, cracked edges, hollow sounds, joint failure, or movement after a freeze and thaw season.For Landscape Architects, specifiers, designers, engineers, contractors, and hardscapers, this is one of the most important distinctions to get right. Geometry, thickness, and installation method directly affect long-term performance.The standards are clear. ASTM, CSA, ANSI, and TCNA classify these paving elements differently for a reason. Once you understand those categories, it becomes much easier to design and build surfaces that perform. CONTACT US Why the Distinction Matters in Real Projects Many failures are not caused by a bad product. They are caused by a mismatch between the paving unit and the installation method.A common example is treating large format slabs or outdoor porcelain like traditional interlocking concrete pavers. They may be strong materials, but strength alone is not enough. If they cannot interlock, they cannot behave like an interlocking system.That is where movement starts: lateral creep under traffic rocking or tipping under load joint shear freeze and thaw related displacement long term settlement issues This is especially important in northern climates, where freeze and thaw cycles expose every weakness in bedding, bonding, and restraint. 1) Concrete Pavers ASTM C936 / CSA A231.2 Concrete pavers are engineered to interlock. Their shape, size, and thickness are all part of that performance.Key characteristics: Max face area: 101 in² Aspect ratio: Length ÷ thickness ≤ 4 Typical thickness: 60 to 80 mm, with 90 mm and 100 mm available for heavier vehicular applications Designed for: pedestrian traffic through to heavy vehicular loads Performance behavior: interlock, lateral load transfer, creep resistance, and permeable system options Concrete pavers work because they are designed as a system element, not just an individual unit. When correctly installed, they transfer loads laterally and maintain stability across the field of pavement.If a unit exceeds the face area limit or aspect ratio limit, it no longer behaves like a true interlocking paver. 2) Concrete Slabs ASTM C1782 / CSA A231.1 Concrete slabs are large format concrete units. They are not the same as concrete pavers.Key characteristics: Face area: Greater than paver limits (ASTM > 101 in², CSA > 0.09 m²) Aspect ratio: Often far above 4:1 Thickness: Less than 60 mm Performance behavior: Limited interlock, relies on bedding support and edge restraint Slabs are an excellent choice for patios and walkways, especially when the design intent calls for a clean, large format look. The issue is not whether slabs are good or bad. The issue is using the right installation approach for a non-interlocking unit. Because slabs are too large to properly interlock, they can: move or creep under load rock or tip if support is inconsistent crack in unsupported areas become unstable in areas exposed to repeated traffic or freeze and thaw movement Slabs should never be treated like small format interlocking pavers, especially in driveways or areas with concentrated loads. 3) Outdoor Porcelain Tiles ANSI A137.1 / A137.3 and TCNA Guidance Outdoor porcelain is in its own category entirely.It is often called a “paver” in the marketplace, but that can be misleading. ANSI ASC A108 approved 2 cm gauged porcelain “pavers” based on strength and performance, not interlock. ASTM, ANSI, and TCNA do not classify outdoor porcelain by plan size in the same way hardscape pavers are classified. How outdoor porcelain is actually classified Outdoor porcelain is defined by: Water absorption: ≤ 0.5% Thickness class: 2 cm or 3 cm Mechanical performance: breaking load, impact resistance, and related performance criteria Sizes like 24x24, 24x48, and 32x32 are market-driven dimensions, not proof of interlocking performance. Can porcelain handle traffic? Yes, porcelain can be extremely strong in compression.That is what causes confusion. A unit can be very strong and still fail in service if the installation method is wrong. The real issue is aspect ratio and movement Outdoor porcelain units typically exceed the hardscape industry’s 4:1 interlocking ratio by a wide margin. That means: they do not interlock they cannot depend on lateral load transfer they should not be installed unbonded where movement is a risk they can creep, shear joints, and drift under traffic or freeze and thaw cycling Another common complaint with poorly installed porcelain is a hollow sound. Proper bonding addresses that issue while also controlling movement. Correct installation for outdoor porcelain Because porcelain is not an interlocking element, it needs a bonded installation system: Bonded to a proper mortar bed, such as ROMEX TRASS BED Installed with a suitable bonding slurry like ROMEX ADHESION ELUTRIANT, which is designed for porcelain tile applications This is critical because not all thin sets bond reliably to porcelain in exterior hardscape conditions.A proper bonded system prevents: lateral creep movement under load de-bonding premature joint and surface failure 4) Why ROMEX TRASS BED Changes the Performance ofSlabs and Porcelain Where interlock is not possible, the system needs to perform another way.ROMEX TRASS BED solves the biggest challenges associated with large format slabs and outdoor porcelain by creating a bonded, stable setting layer that behaves as a monolithic system.What problems it helps eliminate shifting creeping rutting settlement aspect ratio limitations freeze and thaw failures at the bedding layer de-bonding when used with ROMEX ADHESION ELUTRIANT This is the key advantage for designers and contractors working with modern large format materials. You can preserve the aesthetic while restoring performance.Where a bonded TRASS system performsA properly installed ROMEX TRASS BED system can be used for: pedestrian applications driveways high point loads northern freeze and thaw climates open-graded or dense-graded bases If the paving unit cannot interlock, that does not mean the project has to accept movement. It means the project needs the correct engineered bonded system. Best Practice Takeaways for Specifiers and Installers When selecting a paving system, start with geometry and classification first, not just appearance. Ask these questions before specifying or installing Is this unit truly an interlocking paver, or is it a slab or tile? Does the unit meet interlocking geometry limits? What loads will the surface experience over time? Is the site exposed to freeze and thaw cycles? Does the installation method match the material category? These questions can prevent many of the most common hardscape failures and callbacks. The Bottom Line Concrete pavers are small, thick units designed to interlock. Concrete slabs are large format units with limited interlock and greater dependency on bedding support. Outdoor porcelain tiles are strong but non-interlocking and require bonding for stable exterior performance. ROMEX TRASS BED is the engineered solution that restores stability and long term performance where interlock is not possible. In hardscaping, geometry determines behaviour.Interlock is earned, not assumed.When interlock is not available, a bonded system with ROMEX TRASS BED and ROMEX ADHESION ELUTRIANT is how you get performance back.For projects that require durability and permeability, the ROMEX System Guarantee offers a three-part system backed by a 10-year guarantee, which helps specifiers and contractors build with more confidence. FAQ for Designers, Specifiers, and Contractors Are outdoor porcelain tiles considered interlocking pavers? No. Outdoor porcelain may be marketed as “pavers,” but they are not interlocking hardscape pavers in the ASTM/CSA sense. They are classified by performance characteristics like water absorption, thickness, and mechanical strength. Can I install porcelain tiles unbonded on a sand setting bed? In most exterior hardscape applications, that creates a high risk of movement, creep, and joint failure. Because porcelain does not interlock, a bonded installation is the correct approach. What is the main difference between concrete pavers and concrete slabs? Concrete pavers are designed for interlock and load transfer. Concrete slabs are larger format elements with limited interlock and rely much more on consistent bedding support and restraint. Why is aspect ratio so important in hardscapes? Aspect ratio affects whether a unit can interlock and transfer loads properly. Once units exceed interlocking geometry limits, they behave differently and require different installation methods. Why use ROMEX TRASS BED with porcelain or slabs? ROMEX TRASS BED creates a bonded, stable setting layer that helps prevent movement, rutting, settlement, and freeze and thaw related failures, especially where interlock is not possible. CONTACT US

large format slabs

Pavers, Slabs, and Outdoor Porcelain: Understanding the Real Differences in Paving Elements

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large format slabs

Pavers, Slabs, and Outdoor Porcelain: Understanding the Real Differences in Paving Elements

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