Typical block paving defects and repair techniques

The 10 most common block paving defects

1. Too thin a sub-base
2. Too thick a bedding layer
3. Inadequate compaction
4. A waterlogged pavement structure
5. A pavement edge without a kerb
6. Wrong falls, water directed towards the building
7. Jointing material that washes out
8. Mud, clay or topsoil in the base
9. Blocks laid too tightly
10. Commercial "garden" pavers used for industrial loading

Other characteristic defects: poor detailing around utility covers, chamfered or uneven blocks that reduce comfort on cycling surfaces or accessible routes.

Settlement

Causes:

• Uncompacted subgrade or formation
• Weak subsoil with organic content
• A sub-base softened by water
• Too thick a bedding layer (6–10 cm)
• Placing without compaction

The correct repair:

1. Taking up the affected area (marking the blocks for re-laying).
2. Removing the jointing material.
3. Checking the bedding and sub-base – if they are wet, water is the cause.
4. Replacing missing, saturated or loosened material with suitable crushed stone.
5. Re-levelling with a laser.
6. Compacting layer by layer.
7. Rebuilding the bedding layer (3–5 cm).
8. Re-laying the blocks in the original pattern.
9. Jointing and vibrating.

Rutting

Causes:

• A weak base (too sandy, poor grading, not compacted)
• Too thick a bedding layer
• More traffic than designed for
• Industrial loading the build-up was not designed for

Repair:

A surface-only repair (lifting the blocks, topping up the bedding) is rarely durable. The sub-base needs strengthening:

• taking up the affected area,
• reviewing the sub-base and replacing the weak material,
• if necessary, a cement-treated layer in the base,
• re-laying.

Washed-out joints

Causes:

• A drainage fault (standing water, inadequate falls)
• Unsuitable jointing material
• An incompatible jointing material in a permeable system

Repair:

• Find and eliminate the drainage cause (first!).
• Top up the joints with dry, clean fine grit.
• If needed, use a polymeric or stabilised jointing material.
• In permeable systems, only a compatible open jointing material.

Broken or spalled blocks

Causes:

• Laying too tightly (no joints): the movements in the structure cannot be released.
• Improper vibration (a plate compactor without a rubber mat).
• Poor quality blocks (not conforming to UNE-EN 1338).
• Overloading: the block thickness does not match the traffic.

Repair:

• Individual replacement – the neighbouring blocks must be lifted and re-laid.
• Investigating the cause: if the base is weak or the block quality inadequate, a wider intervention is needed.

Repairs around utility covers

This is one of the most problematic detailing tasks. Defects:

• A cover not exactly flush with the paving.
• Small cut pieces around the cover break and fall out quickly.
• A missing concrete collar or special frame.

The correct solution:

• Set the cover to level before paving around it.
• Use pieces larger than 1/3 of a block all around.
• A concrete collar around the cover to take the load.
• Where necessary, a special frame system.

Sunken kerb

Cause:

• No concrete haunching.
• The kerb was "just set down" without a concrete bed.
• The base beneath the kerb is weak or waterlogged.

Repair:

• Lifting the kerb.
• Checking the base and replacing it if necessary.
• Re-concreting with a proper bed and haunching.
• Re-laying the adjacent blocks.

Prevention – the 10-point checklist

• ☐ Is there a design, or at least a layer build-up calculation?
• ☐ Is the bearing capacity of the subsoil known?
• ☐ Is rainwater drainage resolved?
• ☐ Does the block thickness match the loading?
• ☐ Is the sub-base thick enough and well compacted?
• ☐ Is there a stable kerb on a concrete bed?
• ☐ Is the bedding layer not too thick (max. 5 cm)?
• ☐ Are there material certificates and CE marking?
• ☐ Was compaction/bearing capacity testing carried out?
• ☐ Is the condition before covering each layer documented?