20mm Porcelain Tiles vs Standard Porcelain Tiles — What's the Difference?

If you've been browsing porcelain paving and noticed that outdoor products are described as "20mm" while indoor tiles are much thinner, you might be wondering why the thickness matters and whether you could use standard thinner porcelain outdoors. This is a really important question — and the answer is: no, you shouldn't.

Here's everything you need to know about porcelain thickness for outdoor use.

Why Thickness Matters Outdoors

Indoor porcelain tiles are typically 8–12mm thick. They're designed to be laid on a flat, stable substrate inside a building — no thermal movement, no frost, no point loads from heels or furniture legs, and no direct heavy traffic.

Outdoor conditions are completely different:

• Temperature fluctuation: From freezing winter nights to warm summer days, outdoor paving expands and contracts significantly. Thicker slabs handle this stress better.
• Point loads: High heels, chair legs, and the occasional dropped paver tool create concentrated point loads on small areas. Thinner slabs crack under these loads far more readily.
• Substrate imperfections: Even a well-laid mortar bed outdoors isn't as perfectly flat as a screeded interior floor. Thicker slabs bridge minor imperfections better.
• Frost: As water in and around the slab freezes and expands, thicker slabs resist the forces better.
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What Is 20mm Porcelain?

20mm outdoor porcelain (also called "double loaded" or "through-body" porcelain paving) is specifically engineered for exterior use. At 20mm thick, it has:

• Greater flexural strength (resistance to bending and cracking)
• Higher point load capacity
• Better performance in freeze-thaw conditions
• More forgiving installation — minor variations in bed depth are less likely to cause cracking

It's heavier and more expensive than standard 10–12mm porcelain, but for outdoor use, 20mm is the correct specification.

Browse our 20mm outdoor porcelain in our porcelain paving collection and the popular 900x600 porcelain range.

Can You Use Standard (10–12mm) Porcelain Outdoors?

Technically, yes — but it's not recommended, and doing so creates real risk of cracking, particularly on large format tiles. Some installers use 10mm porcelain in sheltered, low-traffic outdoor areas like covered porches or well-protected balconies. For open garden patios, driveways, or any area exposed to UK frost, 20mm is the correct choice.

Using indoor porcelain outdoors also voids any product warranty and may not meet building regulations for certain applications.

Installation Differences

20mm porcelain must be laid on a full solid mortar bed — it cannot be dry-laid on sand, and it cannot be suspended over voids. The mortar bed needs to be continuous with no hollows beneath the slab.

This is a slightly more demanding installation requirement than natural stone (which can tolerate minor voids in the bedding more readily), but it's entirely standard practice for professional installers. See our installation guide for the correct porcelain bedding specification.

One useful practical difference: 20mm porcelain can often be laid as a raised deck system using pedestal supports, which is popular for balconies and roof terraces. The thickness provides the rigidity needed for this application.

Size and Format Considerations

Larger format slabs need to be thicker to maintain adequate rigidity. A 600x600mm slab in 20mm is fine; a 1200x1200mm slab in 20mm may flex if bedding is imperfect. For very large formats, some manufacturers produce 30mm slabs specifically to handle the greater span.

For most domestic garden patios in the UK, 20mm slabs in formats up to 1200x600mm are perfectly appropriate. Formats beyond this are best left to professional installation with very precise bed preparation.

Our size and thickness guide covers recommended thicknesses for different applications and slab sizes in detail.

The Summary

Always use 20mm porcelain for outdoor patios, paths, and driveways in the UK. It's the correct specification, it's widely available, and the small additional cost over thinner indoor tiles is completely justified by improved performance and longevity.