Block paving driveways

Block paving is the most repairable driveway surface there is. Because it is made of separate units bedded on sand rather than one continuous sheet, a block that gets oil on it, cracks or settles can be lifted out and swapped, and the repair vanishes. Nothing else on a driveway does that.

BMS (trading as BMS Building & Groundworks Ltd, formerly BMS Landscaping & Paving Ltd) is a Tobermore Registered Paving Contractor, and lays block paving across Watford, St Albans, Hemel Hempstead and Harrow, along with Borehamwood, Rickmansworth, Bushey and the wider area. BMS also states that it is a Brett Approved Paving Contractor.

The blocks themselves

Two families, and they behave differently.

Concrete blocks are the common choice. They are made in a huge range of colours, finishes and sizes, from plain rectangular blocks through to tumbled and textured ranges that imitate stone. Colour runs through the block on better ranges rather than sitting on the face, which matters after a decade of weather. New concrete blocks usually throw a white bloom for the first few months. That is efflorescence, it is normal, and it washes off.

Clay pavers are fired rather than cast. The colour is the fired clay itself, so it does not fade, and clay holds its appearance for a very long time. Clay is harder, more brittle to cut and generally a more expensive way to do it.

Permeable blocks are a different job rather than a different look. They are laid with wider joints filled with fine grit instead of sand, and they sit on an open graded stone build up that holds water and lets it soak away. That build up is the permeable part. Permeable blocks on a normal sealed sub-base are not a permeable driveway.

How the job is done

The visible part is the last day or so.

1. Dig out. The old surface and enough ground below it come away. Depth is set by what the ground is actually like and what the drive carries, which is settled on site rather than guessed.
2. Sub-base. Crushed stone laid and compacted in layers. Compacting in layers is the part that gets skipped and the part that decides whether wheel tracks appear.
3. Edge restraint. Edging blocks or kerbs bedded and haunched in concrete along every free edge. Block paving is held together by being squeezed. Take the edge away and the blocks creep outwards, the joints open, and the pattern loses its lock.
4. Laying course. A screeded layer of sharp sand, kept at an even thickness and not used to make up for a lumpy sub-base.
5. Laying. Blocks are laid to the pattern, working off the finished levels and keeping the falls running the right way.
6. Cutting. Edges, curves and obstacles cut in. Neat, full sized cuts rather than slivers, because a thin sliver has nothing holding it.
7. Compaction and jointing. The paving is vibrated down onto the laying course, kiln dried sand is brushed into the joints and vibrated again until the joints are full.

Why the pattern matters

Herringbone, laid at forty five or ninety degrees, is the pattern used on driveways for a structural reason rather than a decorative one. Every block is interlocked with its neighbours in both directions, so braking and turning forces get spread across the whole surface instead of pushing one row along. Stretcher bond and basketweave look good on paths and patios but have continuous straight joints that can creep under vehicle loads. Patterns get mixed deliberately: herringbone on the trafficked area, a border in stretcher bond to frame it.

What decides the finish and the lifespan

• Sub-base depth and compaction. The whole thing. Nearly every failed block drive is a base failure wearing a paving surface.
• Edge restraint. Concrete haunching, not sand.
• Falls. Water needs somewhere to go and enough slope to get there. Flat paving holds puddles, and puddles grow moss.
• Full joints. Jointing sand is structural, not cosmetic. It is what transfers load from block to block. Joints that wash out want topping up.
• Cut quality. Full blocks wherever possible, and no thin slivers at the edges.