Question 1

Why has my block paving gone wobbly?

Accepted Answer

Because it has lost its interlock. Block paving is held together by kiln-dried sand packed tight in every joint, pressing against a restrained edge. Empty the joints — usually with a pressure washer — or let the edge course move, and the blocks start working independently. Both are fixable without replacing the drive. It is worth understanding the principle, because it explains everything. The blocks are not fixed down. They sit on a sand laying course and are locked together by friction from the sand in the joints, with the whole field pressing outwards against a perimeter that must be restrained. Load goes into one block, spreads through the joints into its neighbours, and down into the base. Take away either the joint sand or the restraint and that mechanism stops working. The commonest cause is empty joints, and it usually starts with cleaning. A surface cleaner or a lance held close strips the kiln-dried sand out of a joint in seconds. The drive looks immaculate that week and is visibly loose six months later, as blocks move independently, joints widen further and rain washes the bedding sand out from beneath them. Re-sanding and vibrating after any clean is not optional. The second cause is edge restraint, and it explains the movement people find baffling. If the outer course was bedded on sand rather than set on concrete with a haunch behind it, it slowly rotates outwards under load — particularly where cars swing in from the road. The whole field then has room to spread. The blocks that go wobbly are often nowhere near the failed edge; they are just where the accumulated movement has ended up. The third is the base, and that shows up differently. Ruts along the wheel tracks, or a general dishing, mean the sub-base was thin or compacted in one lift and has consolidated under traffic. That needs lifting and rebuilding rather than re-sanding — but the same blocks go back, which is why it is far cheaper than it sounds. The good news is that block paving is the most repairable surface there is. Rebuilding a failed edge and re-laying the loose courses behind it stops the spread at its cause for a fraction of the price of relaying the drive. Cleaning, re-sanding and vibrating restores the interlock. Lifting and rebuilding a settled bay is a day's work. Very few wobbly block drives actually need replacing.

Question 2

Loose blocks on my drive

Accepted Answer

Because it has lost its interlock. Block paving is held together by kiln-dried sand packed tight in every joint, pressing against a restrained edge. Empty the joints — usually with a pressure washer — or let the edge course move, and the blocks start working independently. Both are fixable without replacing the drive. It is worth understanding the principle, because it explains everything. The blocks are not fixed down. They sit on a sand laying course and are locked together by friction from the sand in the joints, with the whole field pressing outwards against a perimeter that must be restrained. Load goes into one block, spreads through the joints into its neighbours, and down into the base. Take away either the joint sand or the restraint and that mechanism stops working. The commonest cause is empty joints, and it usually starts with cleaning. A surface cleaner or a lance held close strips the kiln-dried sand out of a joint in seconds. The drive looks immaculate that week and is visibly loose six months later, as blocks move independently, joints widen further and rain washes the bedding sand out from beneath them. Re-sanding and vibrating after any clean is not optional. The second cause is edge restraint, and it explains the movement people find baffling. If the outer course was bedded on sand rather than set on concrete with a haunch behind it, it slowly rotates outwards under load — particularly where cars swing in from the road. The whole field then has room to spread. The blocks that go wobbly are often nowhere near the failed edge; they are just where the accumulated movement has ended up. The third is the base, and that shows up differently. Ruts along the wheel tracks, or a general dishing, mean the sub-base was thin or compacted in one lift and has consolidated under traffic. That needs lifting and rebuilding rather than re-sanding — but the same blocks go back, which is why it is far cheaper than it sounds. The good news is that block paving is the most repairable surface there is. Rebuilding a failed edge and re-laying the loose courses behind it stops the spread at its cause for a fraction of the price of relaying the drive. Cleaning, re-sanding and vibrating restores the interlock. Lifting and rebuilding a settled bay is a day's work. Very few wobbly block drives actually need replacing.

Question 3

Block paving moving and uneven

Accepted Answer

Because it has lost its interlock. Block paving is held together by kiln-dried sand packed tight in every joint, pressing against a restrained edge. Empty the joints — usually with a pressure washer — or let the edge course move, and the blocks start working independently. Both are fixable without replacing the drive. It is worth understanding the principle, because it explains everything. The blocks are not fixed down. They sit on a sand laying course and are locked together by friction from the sand in the joints, with the whole field pressing outwards against a perimeter that must be restrained. Load goes into one block, spreads through the joints into its neighbours, and down into the base. Take away either the joint sand or the restraint and that mechanism stops working. The commonest cause is empty joints, and it usually starts with cleaning. A surface cleaner or a lance held close strips the kiln-dried sand out of a joint in seconds. The drive looks immaculate that week and is visibly loose six months later, as blocks move independently, joints widen further and rain washes the bedding sand out from beneath them. Re-sanding and vibrating after any clean is not optional. The second cause is edge restraint, and it explains the movement people find baffling. If the outer course was bedded on sand rather than set on concrete with a haunch behind it, it slowly rotates outwards under load — particularly where cars swing in from the road. The whole field then has room to spread. The blocks that go wobbly are often nowhere near the failed edge; they are just where the accumulated movement has ended up. The third is the base, and that shows up differently. Ruts along the wheel tracks, or a general dishing, mean the sub-base was thin or compacted in one lift and has consolidated under traffic. That needs lifting and rebuilding rather than re-sanding — but the same blocks go back, which is why it is far cheaper than it sounds. The good news is that block paving is the most repairable surface there is. Rebuilding a failed edge and re-laying the loose courses behind it stops the spread at its cause for a fraction of the price of relaying the drive. Cleaning, re-sanding and vibrating restores the interlock. Lifting and rebuilding a settled bay is a day's work. Very few wobbly block drives actually need replacing.

Why has my block paving gone wobbly?

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