Holiday
A break in a coating film: somewhere the material never arrived, or arrived so thin that the concrete underneath is effectively bare. The floor around it can be perfect, which is exactly what makes it worth a name.
A gap, and nothing more specific than that
A holiday is a place where the coating is not. Either nothing was applied there, or so little was applied that the concrete underneath is doing the job the film was supposed to do. The term says nothing about how the gap happened, only that the film stopped being continuous.
The old trade joke inside the word is a decent memory aid: the coating took a holiday at that spot. What makes it worth naming is the thing it implies. A coating protects by being unbroken, so a floor is only as good as its worst square inch, never its average one.
Not the same thing as a pinhole
These get used interchangeably and they should not be, because they send you looking in different places for different causes.
A pinhole is a hole through a film that did form. Something worked its way out of the slab or the coating while it was curing and left a channel behind it. A holiday is film that never arrived. One is largely a question of what was coming out of the concrete; the other is a question of coverage, lighting and where somebody was standing.
What they share is the consequence. Both hand anything spilled on that floor a direct route to the concrete, which is why they get talked about together even though almost nothing else about them matches.
Where they hide
Almost never in the middle of the floor, because that is the part everyone can see. They collect at edges and in corners, along the line where a wall meets the slab, behind and underneath equipment that nobody moved, and at the join where a second coat was cut in against an area already coated.
Two conditions turn up again and again in the ones that get missed. Poor light, which removes the only feedback the person applying has. And the end of a pass with a roller that has quietly run dry, which lays a stripe of almost nothing while feeling much like the pass before it. The common thread is that every one of those is a place where you cannot easily see what you have just done.
Why a wet floor will not show you
A wet film is uniformly glossy, and a thin patch looks much like a properly built one for as long as both are wet. The gap that would have been obvious on a dry slab is invisible under the coat, and by the time the material has gone off enough to reveal it, the window for simply working more material into the area has usually closed.
Some never announce themselves visually at all. They are found much later, by a spill, in a floor that otherwise looks excellent. That is the reason the defenses against them are procedural rather than visual: apply to a spread rate you have actually measured rather than estimated, light the space properly before starting, and walk the edges deliberately while the coat can still take material. Back-rolling evens out what is there, but it cannot invent material that was never put down.
A good floor makes it worse, not better
This is the part worth carrying away. A floor that is uniformly a bit thin is at least uniform: it wears in a way somebody notices, and it fails slowly and in the open.
A floor that is right everywhere except one patch behind a rack does the opposite. Every other square foot goes on performing and looking correct, so nothing draws attention to the one place that is not, and the failure gets found late and reads as inexplicable. On a system specified for chemical resistance the arithmetic is harder still, because the resistance is a property of the film. At a holiday you do not have a slightly worse floor. You have bare concrete with a very good floor around it.
No thickness figures are published here. What counts as too thin is a property of the product and its data sheet, and the coverage arithmetic behind it belongs to the film thickness tools rather than to a definition.
Frequently Asked Questions
What is a holiday in a coating?
It is a gap. Somewhere on the floor the coating is missing, or is so thin that whatever the film was meant to do is not happening there.
The word is old trade usage and the joke inside it is accurate enough to be a good memory aid: the coating took a holiday at that spot. It is not a description of how the gap got there, only that the film is not continuous.
That is the whole point of the term. A coating works by being unbroken, so a floor is only as protected as its worst place, not its average one.
Is a holiday the same as a pinhole?
No, and the distinction is practical rather than pedantic.
A pinhole is a small hole through a film that did form: something escaped through the coating as it cured and left a channel behind. A holiday is film that never arrived in the first place. They have different causes, they are found in different places, and one of them is a coverage and technique problem while the other is usually about air or moisture coming out of the slab.
They do have one thing in common, which is that both give anything spilled on the floor a route to the concrete.
Where do they usually hide?
Wherever attention runs out, which is rarely the middle of the floor.
Edges and corners, the line where a wall meets the slab, behind and underneath equipment that was not moved, and the join where a second coat was cut in against an area already coated. Poor light is a reliable contributor, and so is the end of a pass with a roller that has run dry without anyone noticing.
The common thread is that all of those are places where the person applying could not easily see what they had just done.
Why are they hard to see?
Because a wet floor is uniformly shiny, and a thin spot looks much like a properly built one until it is not wet any more.
A gap that was obvious in the pail is invisible under a wet film, and by the time the coat has gone off enough to show it, the window for simply rolling more material into it has usually closed. Some never show visually at all and only announce themselves later, when something gets spilled and the concrete underneath takes it.
This is why the defenses are procedural rather than visual: work to a spread rate you have actually checked, light the area properly, and walk the edges deliberately before the coat sets rather than after.
Does it matter if the rest of the floor is right?
It matters more, not less, and that is the counterintuitive part.
A floor that is uniformly a little thin is at least uniformly a little thin, and it fails slowly and visibly. A floor that is correct everywhere except one patch behind a rack fails at that patch while every other square foot goes on looking excellent, so the failure gets found late and reads as a mystery.
On a system chosen for chemical resistance the arithmetic is starker still: the resistance belongs to the film, so at a holiday you do not have a slightly worse floor, you have bare concrete.