Joint and Crack Repair
Semi-rigid joint fill and structural crack repair. On its own where the floor is otherwise fine, or as preparation before polishing or coating.
Why control joints break down
Control joints are cut into a slab on purpose. Concrete shrinks as it cures and moves with temperature, and the joint gives that movement somewhere to go so the slab cracks where you chose rather than where it likes.
The problem is what happens at the edges. An open joint has two unsupported concrete edges standing proud, and every wheel that crosses them chips a little more away. That is spalling, and once it starts it accelerates. A forklift crossing an open joint hits the edge as an impact rather than rolling over it.
Left long enough, a joint that was three millimetres wide becomes a ragged trench, and what began as a maintenance job becomes a repair one.
Why the filler is semi-rigid
This is the part that gets specified wrong, and it is the reason joint repairs fail.
A soft, flexible sealant works in a wall or an expansion joint, where the point is to absorb movement. Put it in a floor control joint carrying wheeled traffic and it compresses under load. The wheel pushes it down, the joint edges take the impact anyway, and the spalling carries on.
A rigid filler goes the other way. It carries the load but has no give at all, so the slab movement the joint exists to accommodate has nowhere to go and cracks the filler, the joint edge, or both.
Semi-rigid filler is the answer for a floor joint. Hard enough to support the joint edges so wheels roll across rather than into them, with just enough give to tolerate the slab moving. It is filled flush and ground level with the floor, so there is no lip left to hit.
Cracks are a different question
Before anything gets filled, a crack has to be understood rather than covered.
Dormant cracks
The slab has moved, settled, and stopped. These are a surface problem. They get cleaned out, filled and ground flat, and they stay fixed. Most cracks in an older floor are this.
Live cracks
The slab is still moving, usually because of something underneath it. Fill a live crack and it comes back through whatever you put over it, including an overlay. Filling it is not a repair, it is a delay.
Telling them apart is a judgement made on site, and it is the difference between a repair that holds and one that reappears next year. If a crack is live, we say so rather than filling it and moving on.
On its own, or as preparation
Most of this work happens as the repair stage inside a larger job. The slab gets ground open, the joints and cracks get filled and levelled, and then the floor is polished, coated or sealed. Doing it in that order matters, because filling after the finish leaves the repair sitting on top of it.
It is also a standalone job. Where a warehouse floor is otherwise sound but the joints have started to spall, filling them stops the damage before it spreads, and it costs a fraction of what fixing a trench costs later. It is the cheapest concrete work you can do and the easiest to put off.
Before, during and after
What it costs
Joint filling is priced by linear foot rather than by area, because that is what the work actually is. Crack repair depends on how much there is and how deep it goes.
As part of a larger floor job it is included in the quote for the finished floor. As a standalone it is quoted on its own, and it is usually a small number against what it prevents.
The comparison worth making is against doing nothing. A joint filled now costs a fraction of a joint rebuilt in two years.
Common questions
Why are my control joints chipping at the edges?
That is spalling, and it happens because an open joint leaves two unsupported concrete edges standing proud. Every wheel that crosses hits them as an impact rather than rolling over. Filling the joint supports the edges so traffic rolls across instead.
Why does the filler need to be semi-rigid?
A soft sealant compresses under a wheel, so the joint edges still take the impact and keep spalling. A fully rigid filler has no give, so slab movement cracks it or the joint edge. Semi-rigid supports the load and still tolerates the slab moving.
Will a filled crack come back?
A dormant crack that is cleaned out, filled and ground flat stays fixed. A live crack, where the slab is still moving, will come back through anything put over it. Telling them apart is part of the site visit.
Can you do joint repair without redoing the whole floor?
Yes, and on a sound warehouse floor with spalling joints that is often the sensible job. It stops the damage spreading and costs a fraction of what a rebuilt joint costs later.
Should joints be filled before or after polishing?
Before. The slab gets ground open, joints and cracks are filled and levelled, and then the floor is finished. Filling afterwards leaves the repair sitting on top of the finish rather than in the floor.
Book a site visit
We look at the joints and the cracks, tell you which are live and which are dormant, and quote the work that will actually hold.