Expansion Joints and Edges: The Weak Points of Outdoor Concrete
Joints and edges are where outdoor concrete fails first, because that is where it moves most and is least supported. A broken expansion joint should be cleaned out and restored so it can keep working, not filled solid. Chipped edges along walls, steps and posts are rebuilt and cut in by brush before recolouring. A joint where the slabs have dropped out of level points to movement and needs assessing first.
Send us a photo and the m²What does an expansion joint actually do?
An expansion joint, or more broadly a movement joint, is a deliberate break in a slab that lets each section expand, contract and shift slightly on its own. Without it, the stresses build up until the slab cracks wherever it is weakest.
Some joints run right through the slab and are filled with a flexible material; others are cuts in the surface that make the slab crack in a straight, hidden line underneath. On imprinted concrete, these cuts are usually placed along the pattern so they are hard to see.
Either way, a joint is doing its job when the cracks happen inside it rather than across the open surface.
Why do joints fail?
Joint fillers age in the sun, harden, shrink and pull away from the concrete. Once there is a gap, soil and seeds fill it, roots widen it and water runs underneath the slab.
Traffic then breaks the unsupported edges either side of the joint, which turns a neat line into a ragged channel. On driveways, the joint across the entrance and the ones near gates usually go first.
- Perished or missing joint filler.
- Weeds and soil in the gap.
- Chipped or broken edges along the joint.
- Water pooling at the joint or draining under the slab.
- Cracks running out from the end of a joint.
Why is filling a joint solid a mistake?
A rigid fill takes away the slab's freedom to move. The movement does not stop, so the stress goes somewhere else, often producing a new crack a short distance away from the old joint.
A professional joint repair cleans the joint out, rebuilds broken edges back to sound concrete, and restores the joint with a material intended for movement joints, following its data sheet. Our expansion joint repair page explains how we do this.
Why do edges break before the rest of the slab?
Edges are the thinnest and least supported part of a slab. Where concrete meets a wall, a pergola post, a step, a planter or a drain, it is also where water runs and collects, and where the ground underneath is most likely to have been disturbed during building.
That combination makes edges chip, crumble and crack earlier than the open surface. They are also where cracks often start, which links edge damage to crack repair.
How are edges repaired and finished before recolouring?
Broken or crumbling edges are cleaned back to sound concrete and rebuilt so they sit flush with the surface. Masking is used where the edge meets a wall or a surface that should not be coloured.
Before the main surface is coated, the borders along walls, posts and steps are cut in by brush. A roller cannot reach those spots cleanly, and a neat cut-in line is a large part of what makes the finished surface look professional rather than patched.
On the Marbella imprinted driveway, this edge work around the pergola posts and walls came before the colour; see imprinted concrete repair for the full sequence.
When do joint and edge problems point to movement?
When the slabs either side of a joint are at different heights, when a joint keeps getting wider, or when edges along a wall have dropped away from it, the ground or base is likely to be moving. Repairing the joint does not stop that movement.
In those cases, an engineer or surveyor should look at the cause first. Our guide to crack types describes the same warning signs for cracks.
Which joints and edges on a villa tend to need attention?
On a typical villa plot the problem spots are predictable. Driveway entrances and gate tracks take turning traffic, carport edges sit against posts and walls, and pool surrounds meet copings and drainage channels.
- The joint across the driveway entrance and near the gate.
- Borders along boundary walls and retaining walls.
- Edges around pergola and carport posts.
- The line where a terrace meets the pool coping.
- Steps, thresholds and the edges of planters.
When you send photos, include these spots even if they look minor. Small edge damage caught early is much simpler to repair than a long broken run.
How can joints and edges be kept in good order?
Keeping joints free of weeds and soil, making sure downpipes and irrigation do not discharge along an edge, and dealing with a perished joint before the edges break up all extend the life of a surface.
On recoloured surfaces, gentle cleaning in line with the coating's data sheet keeps joint lines crisp. If an edge starts to chip, repairing it early is a much smaller job than rebuilding a long broken section later.
Frequently asked questions
What is a broken expansion joint?
It is a movement joint in a slab where the filler has perished or come out and the edges either side have chipped or crumbled. Water, soil and weeds get in, and the damage spreads along the joint and sometimes into new cracks nearby.
Do all concrete driveways have expansion joints?
Most properly laid driveways have some kind of movement joint, either full-depth joints with a flexible filler or cuts in the surface that control cracking. On imprinted concrete the cuts often follow the pattern, so they can be hard to spot.
Can I fill an expansion joint with cement?
Filling a movement joint with rigid material such as cement or mortar takes away its purpose. The slab still moves, so it tends to crack next to the filled joint. Joints should be restored with material intended for movement joints, applied as its data sheet describes.
Why are the edges of my patio crumbling?
Edges are the thinnest and least supported part of a slab, and often where water runs or collects. That makes them wear and break before the rest of the surface. If the edge has also dropped or pulled away from a wall, ask for an assessment for movement.
What does cutting in mean on a concrete repair?
Cutting in is painting the borders by brush along walls, posts, steps and other edges before rolling the main surface. It gives a clean, straight colour line in places a roller cannot reach neatly, and it is a large part of what makes the finish look professional.
Can joints in imprinted concrete be repaired?
Yes. The joint is cleaned out, broken edges are rebuilt and the joint is restored, then the surface is recoloured. Because these joints usually follow the stamped pattern, the restored lines tend to blend into the design once the colour is even.
What does it mean if slabs are uneven at a joint?
A height difference at a joint means one section has moved, usually because of something in the ground or base. That needs a qualified engineer or surveyor to assess before any joint or surface repair, because repairing the joint will not stop the movement.
Why do weeds keep growing in my driveway joints?
Weeds grow where joint filler has perished and left a gap that fills with soil. Pulling them out only helps briefly. Cleaning out and restoring the joint removes the gap, which is what stops them returning in the same place.
Should joints be painted over when a driveway is recoloured?
Joints should stay as working joints. The coating is applied so that the joint lines remain visible and able to move. Painting a joint shut tends to produce an untidy crack along it later, which spoils the look of the recoloured surface.
Is this guide a DIY joint repair method?
No. It explains how joints and edges work and how professionals approach them, so you can understand what you are being quoted for. We do not provide do-it-yourself instructions or product recommendations for home repairs, because the right material depends on the joint and its data sheet.
How do I know where the joints in my driveway are?
Look for straight lines across the width of the driveway, often at regular intervals, or along the edges of the pattern on imprinted concrete. If you are not sure, send us photos and we can point out the likely joint lines when we reply.