This one is written for the person who looks after the building rather than the person who designed it: the facility manager of a mall or hospital, the estate engineer of an IT park, the maintenance head who walks the same concourse every week and has started to notice something.
The five signs below are in the order we usually meet them — earliest and cheapest to fix first, most expensive last. The useful thing about that ordering is that the first two are almost free to put right and the last two are not, and the gap between them is often eighteen months of doing nothing.
1. It has started to make a noise
What you notice. A click, a knock or a metallic rattle as a trolley or a footfall crosses the cover. It is usually worse in the afternoon, worse in summer, and you can often reproduce it by standing on one edge of the plate and rocking.
What it means. The cover plate is moving against its frame in a way it was not built to. On a joint designed to be silent, that means a fixing has lost its grip, the anchor has worked in its hole, or the plate has lost the component that holds it centred. This is the single most common early sign of failure we are called to, and it is a fixing problem long before it is a joint problem.
How urgent. Low urgency, high value. A joint that rattles is still doing its job. Left alone, though, every crossing works the anchor a little further and the hole gets larger; that is how a rattle becomes a lifted plate and then a tripping hazard.
What to do this week. Have someone check the fixings along the noisy run and record which positions are loose. If they can be re-torqued into sound concrete, the job is an hour. If they spin freely, the concrete around them has gone and the repair is a substrate repair, not a re-tighten — see sign 5.
A rattling joint is a warning, not a nuisance. It is the cheapest moment the building will ever offer you to fix that joint.
2. The cover sits proud, has lifted at one end, or has moved along the line
What you notice. A lip you can feel through a shoe or a trolley wheel. One end of a cover length standing above the finish. A cover that has crept along the joint so the gap between lengths has opened at one end and closed at the other. Sometimes a screw head standing above the plate.
What it means. Either the fixings have released (sign 1, one stage further on) or the joint has been asked for more movement than it was rated to give and has walked. The second of those is a specification problem, not a maintenance one, and it will come back unless the replacement is sized against the movement rather than the hole — the reasoning is in how to read a movement capacity table.
How urgent. Medium, and it moves to high the moment the public can catch a foot on it. A proud edge in a hospital corridor is a trolley problem and a trip claim before it is an engineering problem.
What to do this week. Photograph it end to end, measure how far the cover has moved from its original position, and stop anyone from screwing it back down flat with longer fixings. Fixing the symptom that way pins a joint that is trying to move, and the next thing that yields is the concrete.
3. The floor finish alongside the joint has tented, cracked or drummed
What you notice. Tiles or stone lifting into a ridge a few hundred millimetres away from the joint, sometimes with a hollow sound when tapped, sometimes with grout crushed to powder along one line.
What it means. This is the one that looks like a joint failure and usually is not. The structural joint is doing what it should; the finish has no movement joint of its own over the top of it, or the one it had has been grouted solid, so the tiled field is taking the movement instead and failing in compression. Why tiled and stone floors tent covers the mechanism in full.
How urgent. Medium. Tenting rarely stops spreading on its own, and each season adds length to the failed run.
What to do this week. Before anyone re-lays tiles, find out whether the movement joint in the finish exists at all. Replacing the tiles without it buys you the same failure on the same line, usually within a year.
4. There is a stain, a drip or efflorescence below the joint line
What you notice. A patch on a basement soffit, a rust run down a car-park beam, white salts on the underside of a podium, a ceiling tile in the floor below that keeps being replaced. Often the wet patch is several metres from the joint and nobody connects the two.
What it means. Water is getting past the waterproofing at the joint and running along the slab soffit until it finds a low point or a penetration to drip from. That is why the stain is almost never directly under the fault. The usual culprit is not the middle of the membrane but its termination — the lap where it should bond to the structural waterproofing either side, or an upstand that was never formed. Where the joint meets the waterproofing sets out who is supposed to own that lap.
How urgent. High, and higher than it looks. Water at a slab edge does two things at once: it corrodes reinforcement in the most congested concrete in the structure, and it softens the substrate the joint's own fixings depend on. A leak left for two monsoons turns a joint replacement into a joint replacement plus a concrete repair.
What to do this week. Record where the water appears and when — during rain, hours after, or continuously (a continuous drip in dry weather is a services leak, not the joint). Then trace the joint line above it. Do not inject or seal the visible damp patch; sealing the exit does not stop the entry, it just moves the next one along.
5. The gap itself has changed, or something is living in it
What you notice. A gap that is visibly wider at one end of a run than the other. A gap packed with grit, stones, cement droppings or the remains of a filler board. A gap that someone has “repaired” with mortar, tile adhesive or a bead of sealant.
What it means. A gap that varies along a run is normal within limits — on nearly every building we survey the built gap differs from the drawn one. What is not normal is a joint that has been filled. Mortar or adhesive in a movement gap converts a designed joint into a crack, and the structure then cracks somewhere the designer did not choose. Packed debris does the same thing more slowly: it stops the joint closing, so the next hot season takes the load out on the frames and the slab edges.
How urgent. Depends entirely on what is in it. Loose debris is a cleaning job. A mortared-up joint is a structural conversation, because whatever movement was supposed to happen there has been going somewhere else since the day it was filled.
What to do this week. Photograph anything sitting in the gap, and find out when it was put there and by whom. On commercial buildings it is very often a later tenant fit-out that tiled over, boxed in or drilled through a working joint.
What to have ready before you call anyone
Whoever you call — us or anyone else — these five things turn a site visit into a diagnosis, and most of them take a phone and a tape:
- Photographs along the joint line, and close up at the worst point.
- The gap measured at three points on one continuous run, with the ambient temperature at the time you measured. Without the temperature a single measurement is not usable — a gap read on a 43 °C afternoon is at its most closed.
- What is underneath — occupied space, a basement, a car park, external air.
- The age of the building, and anything that changed in the area before the symptoms started: a fit-out, a re-tiling, a new services run.
- When the symptom appears — only in the rain, only in summer, only under trolleys, or all the time.
From those we can usually tell you which of the four things that actually fail you are looking at, and whether what you need is a fixing job, a substrate repair with a new joint on top, a flooring job, or nothing at all. The order that work has to happen in — and why doing it in the obvious order produces a replacement that fails faster than the original — is in replacing a failed expansion joint, in the right order.
The two things not to do
Do not seal it. The instinct when a joint leaks or rattles is to run a bead of sealant or a screed of mortar into it. Every joint we are called to that has been treated this way has failed again within a season, usually having taken a slab edge with it.
Do not wait for the monsoon to decide. The cheapest month to work on a joint is a dry one, in a building that is not yet leaking. Once water is entering, the survey has to happen anyway — but now it happens with a wet substrate, an occupied floor below and a programme set by somebody else.