How To Repair A Sunken Or Uneven Block Paved Driveway

A block paved driveway that has developed sunken, raised or uneven areas is not only unsightly but can also become a trip hazard and, if left unaddressed, can deteriorate further over time.

The good news is that one of the great advantages of block paving over other driveway surfaces is that individual areas can be lifted, repaired and re-laid without disturbing the rest of the driveway. Here is what causes unevenness in block paving and what is involved in putting it right.

What Causes A Block Paved Driveway To Sink Or Become Uneven?

Understanding the cause of the problem is important before any repair work begins, as addressing the symptom without tackling the underlying issue will result in the same problem recurring.

Sub-Base Failure

The most common cause of sinking or unevenness in a block paved driveway is failure of the sub-base beneath the blocks. The sub-base is the compacted layer of crushed stone or hardcore that forms the foundation of the driveway.

If this layer was not compacted sufficiently during the original installation, if it has been undermined by water ingress or tree roots, or if it was simply not deep enough for the loads being placed on it, it can settle unevenly over time, causing the blocks above to follow the movement of the ground beneath.

Drainage Problems

Poor drainage is a frequent contributor to sub-base failure. Where water is allowed to accumulate beneath the blocks rather than draining away freely, it can wash fine material out of the sub-base and soften the ground beneath, creating voids that cause the surface above to sink.

Blocked or inadequate drainage channels, missing edge restraints that allow water to escape around the perimeter and low points in the surface that allow pooling are all common causes of water-related sub-base problems.

Tree Root Activity

Tree roots growing beneath a driveway can cause blocks to lift and become uneven as the roots expand and push upward. This type of damage tends to follow the line of the root rather than affecting a random area of the surface, which can help to identify the cause even before the blocks are lifted.

Poorly Compacted Sand Bed

The blocks themselves sit on a layer of sharp sand, which provides a consistent, level bedding surface and allows minor adjustments during laying. If this sand bed was not laid to a consistent depth or was not properly compacted, the blocks above may settle unevenly over time as the sand redistributes under vehicle loading.

How Is A Sunken Or Uneven Block Paved Driveway Repaired?

Lifting The Affected Blocks

The first step in any block paving repair is carefully lifting the blocks in the affected area. One of the practical advantages of block paving is that individual blocks can be removed without damaging them, allowing them to be re-laid once the underlying problem has been resolved.

The blocks should be removed methodically and stacked carefully so that they can be returned to their original positions, maintaining the existing pattern and avoiding the need for new materials in most cases.

Addressing The Underlying Cause

Once the blocks have been lifted, the cause of the problem can be properly assessed and addressed. Where the sub-base has failed, the affected material needs to be excavated, any soft or waterlogged ground beneath allowed to dry out and stabilise, and a new, correctly compacted sub-base reinstated to the appropriate depth.

Where drainage is the root cause, this needs to be resolved before the sub-base is reinstated, otherwise the same problem will return.

Where tree roots are responsible, the decision about how to manage them needs to be considered carefully. Simply cutting the roots without addressing the tree itself may not provide a long-term solution, and advice from a qualified tree surgeon may be appropriate before the repair proceeds.

Relaying The Blocks

With the sub-base reinstated and any drainage issues resolved, a fresh layer of sharp sand is laid and screeded to the correct level, and the blocks are re-laid in their original pattern.

The re-laid area is then compacted using a plate compactor, jointing sand is brushed into the joints and the surface is compacted again to bed the sand fully into place.

Where any blocks have been damaged during the original problem or during the lifting process, replacement blocks will be needed.

Finding an exact match for older block paving can sometimes be challenging, as colour batches and product lines change over time, which is worth bearing in mind when managing expectations about the finished appearance of the repaired area.

Can You Repair Block Paving Yourself?

Minor repairs involving a small number of isolated blocks can sometimes be managed by a competent DIYer, but any repair that involves addressing a failed sub-base, resolving drainage problems or relaying a significant area of blocks is best left to an experienced paving contractor.

Incorrectly reinstating the sub-base or sand bed will result in the same problem returning, often within a relatively short period, and the cost of having the work done again will far exceed the cost of having it done correctly in the first place.

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