Why Do Paving Slabs Crack And How To Repair Them

January 1, 2024

Seeing cracks appear on your patio or driveway can be disheartening after investing time and money into installing beautiful paving. Unfortunately, cracks happen for reasons often beyond your control. But don't worry - cracked paving slabs don’t necessarily mean you need to start from scratch. Depending on the severity, there are affordable ways to fix cracked paving and restore your space.

What Causes Paving Slabs To Crack In The First Place

Ground Settlement

The most common cause of cracks is ground settlement underneath the patio. If the sub-base under your paving was not compacted properly for your soil type, the ground will likely settle unevenly over time. This soil movement places stress on the paving structure, eventually causing visible cracks or raised edges as slabs tilt out of place. Clay and other expansive soils are most vulnerable to shifting and subsidence issues as moisture levels fluctuate dramatically between rains and droughts. But concrete or gravel bases can also settle and transfer cracks to the surface. A thicker sub-base minimises sinking risks over decades of use.

Soil Shrinkage & Heave

Similarly, soils like heavy clay alternate between shrinking and expanding as they dry out or become saturated after storms. Cycles of extreme drought then heavy rain can make the ground underneath a patio rise and drop, lifting or settling paving slabs above. This inevitably strains slab joints until cracking damage appears - usually during summer or after winter freezes.

Poor Installation Techniques

Laying paving without full mortar support also frequently causes later cracking. Dot-and-dab installs with just mortar dots or corners leave hollow areas for water to pool and freeze, weakening pavers over time. Fully bedding slabs across a concrete or 4:1 mortar base prevents these issues.

How To Repair Cracked Paving

If your patio has cracks, all is not lost! Here are four practical solutions to restore your surface:

1. Slab Resurfacing

Resurfacing covers cracks with fresh paving laid over the damaged layer beneath. But hairline cracks often continue growing until they mar the new surface too. Resurfacing alone rarely resolves uneven sinking or soil issues under the original slabs.

2. Mudjacking

Mudjacking lifts sunken slabs by injecting mortar mixture to fill voids via holes drilled through the paving surface. It works well for concrete repairs but poses challenges on softer natural stones that can crack under pressure. And later soil settling can sink heavy mortar just like original slabs.

3. Polymer Packing

For a lighter support approach, polymer packing pumps expanding polyurethane foam under slabs instead of concrete mortar. The foam lifts gently and leaves durable support that won’t contribute weight to re-sink patios. Polyurethane offers an excellent modern solution for raising concrete pads and preventing additional cracks long-term.

4. Spot Slab Replacement

Replacing just a few damaged slabs keeps costs affordable. Simply lift the compromised pavers, rebuild the base layer properly with packed gravel and fresh concrete, then relay replacement slabs seamlessly anchored to stable surroundings.

Prevention Is The Best Solution

No patio lasts indefinitely. But quality materials made for local conditions, installed properly atop a well-graded base of adequate thickness, will make paving withstand decades rather than just years of family use before cracks appear. Pay careful attention to drainage and moisture levels around the perimeter too - allowing the underlying soil to alternate between bone dry and saturated greatly accelerates shifting and damage. With a quality foundation and mindful care, beautiful paving can last 50 years or more before major overhaul. Don't let a few cracks spell complete disaster - timely repairs keep patio problems minor.

"As a professional landscaper, proper base preparation is absolutely crucial. Compacting gravel and precision grading prevent 90% of paving slab cracks down the road. If issues do arise later on, targeted mudjacking or replacing single slabs saves big money compared to fully reinstalling an entire patio." - Steven Bell, Paving Shopper Landscapes

Do porcelain patio slabs crack easily?

When properly installed on a stable base, porcelain pavers are very durable and no more prone to cracking than concrete or natural stone alternatives. Their dense composition makes porcelain patio tiles quite resilient against cracks.

Why do my sandstone patio slabs keep cracking?

Sandstone is prone to cracking from ground settlement issues because it has naturally occurring cracks and fissures. Freezing conditions readily infiltrate its porous surface and undermine sandstone’s structural integrity from below over time. Preventing extensive cracks requires installing sandstone on an exceptionally stable, thick base.

Can freezing weather cause cracks in limestone paving?

Absolutely. Like sandstone, limestone contains tiny natural pores that allow water to penetrate the material. When this moisture freezes and expands inside limestone, unseen cracks start forming. Over many winter freeze/thaw cycles, visible cracks, pits, and flakes begin marring the surface.

Do porcelain patio slabs crack when frozen?

No, porcelain patio pavers do not readily crack from winter freeze/thaw issues since they have an exceptionally dense, non-porous composition. Water cannot easily penetrate into porcelain to expand, form cracks and undermine its sturdy surface integrity over time as it does more porous materials. Installing porcelain on a good patio sub-base can help prevent issues with cracking.

Why is sandstone prone to worse cracking from ground freezing?

Sandstone contains abundant tiny natural pores and cracks which allow ground moisture easy access inside the stone. When this water freezes and swells up within sandstone slabs over winter, invisible cracks steadily grow. After years of exposure, visible cracks, pits, and surface flakes develop from the cumulative freeze damage.

Can extensive moisture exposure and freezing weather eventually crack through limestone?

Yes. Like sandstone, the natural pores and microscopic cracks in limestone give external water sources multiple access points to infiltrate the material. Each winter when this moisture freezes and expands below the surface, more microscopic fractures form. Over time, accumulating freeze fractures create visible surface cracks and degrade the integrity of limestone paving.

What makes porcelain paving exceptionally resistant to winter cracking?

Porcelain’s incredibly dense, near-porous structure leaves water no pores or cracks to ingress through. With no moisture penetration, freezing temperatures cannot expand ice within the material and leverage this immense internal pressure to steadily split porcelain from the inside out each winter. This unique composition makes porcelain highly impervious to freeze-thaw damage.