Movement joints exist to let a building or a floor move, and they are the one place where protection has to be deliberately weak. Covering them like anywhere else stops them working, and the result is damage at the joint edges that is expensive and easy to prevent.
What the joint is for
A large floor moves with temperature and with the structure, and the joint absorbs that movement. If something rigid bridges the joint, the movement has to go somewhere – and it goes into the floor either side, which produces cracking at the joint line, tenting, or a crushed edge. On a big floor plate this is a real force, not a theoretical one.
Do not bridge it
The rule is simple: protection stops on both sides of the joint and does not cross it. That leaves a gap, which is a wheel hazard and a trip hazard – so the gap needs managing rather than eliminating. A cover that is fixed to one side only and slides over the other is the standard detail, and it does both jobs.
Managing the gap
A chamfered edge on both sides reduces the trip risk to almost nothing for foot traffic. For wheeled traffic, a cover plate that is fixed on one side and free to slide on the other gives a continuous surface without restraining movement. Both are cheap details and both are specific to the joint – using either everywhere would be overkill.
Where joints get missed
Movement joints are shown on the floor plan and then forgotten once the floor is laid, because modern joints are often discreet. Whoever lays the protection needs the joint locations from the drawing, not from looking at the floor. Getting that information at the start is a two-minute ask that prevents the most expensive version of this mistake.
What happens if it is bridged
Usually nothing for weeks, and then a crack or a lifted edge at the joint. It is the kind of damage that appears after handover and gets blamed on the flooring contractor, and by then the protection is long gone and the cause is not obvious. Worth a photograph of the joint detail before the protection goes down.
How much a joint actually moves
A movement joint in a large floor might accommodate a few millimetres over a season, which sounds negligible and is enough to crush an edge if something rigid spans it. It also means the cover has to accommodate movement in both directions, not just opening. A sliding cover plate fixed on one side does that; a plate fixed on both sides does not, whatever it looks like.
Joints in screed versus joints in the structure
Two different things get called movement joints. One is in the floor build-up, put there to control cracking in a screed. The other is in the building structure and passes through everything including the floor finish. The second is the one that must not be bridged, and telling them apart from the drawing is worth doing properly before specifying anything.
What a bridged joint looks like later
Usually a crack parallel to the joint, or a lifted edge at one side. It gets blamed on the flooring, and by the time it appears the protection is long gone. Photographing the joint detail before the cover goes down is the only cheap way to have the answer ready.
The arrangement that works is a PP honeycomb panel either side of the joint with a sliding cover plate over it. Corrugated PP sheet laid straight across will restrain the joint eventually, however light it looks.
What we can do
We supply joint cover plates fixed one side and free the other, and chamfered edge trims for foot-traffic joints. Tell us where the joints are and what crosses them, and we will specify per joint rather than per square metre. Floor joint behaviour is touched on in floor panel joints that are not trip hazards.