Why is there a curing compound on the slab at all?

Because concrete has to be cured, and spraying a film is the cheapest way to do it on a large floor. Curing means keeping enough water in the concrete for the cement to keep reacting, and it is a requirement rather than an optional extra. ACI 308, the American Concrete Institute guide the industry works to, treats curing as part of placing concrete properly. The alternatives are labor: keeping a slab wet, or covering it in sheeting and tending it for days. A sprayed membrane is one pass with a hand sprayer and it needs nobody to come back. So the film is not carelessness. It is somebody meeting an obligation in the cheapest compliant way, on a slab that nobody had yet said would be coated. Reading it as a mistake leads to the wrong conversation with the wrong person.

What is the difference between a curing compound and a cure and seal?

One is designed to go away. The other is designed to stay. That single difference decides how much of your day you lose, and almost nobody on the concrete side is thinking about it when they buy. ASTM C309 covers liquid membrane-forming compounds for curing concrete. Their job is to hold water in while the concrete gains strength, and that job ends. ASTM C1315 covers liquid membrane-forming compounds with special properties for curing and sealing, which adds requirements around gloss and durability, because the product is meant to remain on the floor as a sealer afterward. That is what the word seal in cure and seal is telling you: somebody bought a product engineered to be permanent. It is still coming off before you coat, but you are now removing something built to resist exactly that, rather than something that was always going to be temporary. Ask which one was used, and ask for the product name rather than the category.

The builder says they used a dissipating one. Does that help?

Less than it sounds, and the reason is worth knowing before you price on it. Dissipating compounds break down under UV and traffic. Neither of those is spread evenly across a floor, and indoors there is often no UV at all. The result is a slab that has lost the compound exactly where you would think to check and kept it under racking, along the walls, in the corners and anywhere that stayed covered. So treat it as information about the product rather than as a reason to change the plan. The detail, and what it does to a prep pass, is covered in removing sealers and curing compounds.

What should I ask for before the slab is poured?

Three things, and this is the only moment any of them is cheap. Ask for the curing method to be one you can live with. Wet curing or sheet curing leaves nothing behind at all. If a membrane is going to be used, ask for a curing compound rather than a cure and seal, because you are then removing something intended to be temporary. Ask for the product name in writing, recorded against the pour. Not the category, the actual product, because the data sheet answers questions later that nobody will remember. And ask that whatever is chosen is stated by its manufacturer to be compatible with a subsequent coating. Plenty are not, and the ones that are not do not announce it on the drum. None of this costs the concrete contractor anything if it is raised early. All of it becomes a variation, an argument or your problem if it is raised late.

Nobody knows what was applied. What now?

That is the normal case, not the unlucky one, so build for it rather than chasing it. When there is no record, you stop trying to identify the product and start testing the slab in front of you. Find out whether there is a film and where it is, because coverage is almost never uniform, then prep as though it is present everywhere and confirm on the prepared surface rather than on anybody’s assurance. Price it that way too. A slab with an unknown treatment is not the same job as a bare slab, and the honest response is to say so in the quote rather than absorb it and hope.

Should I warrant a floor over a compound nobody can identify?

You can, but only on the basis of what you verified rather than what you were told, and the difference should be visible in the paperwork. What protects you is not knowing the product name. It is having prepared to bare, sound, opened concrete, having confirmed that on the prepared surface, and having a moisture reading taken after the film came off rather than before. Those are things you did and can evidence. What does not protect you is a verbal assurance that the compound was dissipating, or that it was applied a long time ago, or that another trade coated over one once without trouble. If the slab has not been prepared and tested, the unknown compound is still an unknown, and a warranty written over it is a warranty written over somebody else’s purchasing decision.

Cure and Seal Compounds: The Builder’s Sealer Problem

Somebody sprayed a film onto your slab months before you were asked to quote, for good reasons, and nobody wrote down which product it was. The decision that creates the problem is made before you are in the room.

It is not carelessness, it is compliance

Nearly every new slab arrives with a film on it, and the coating trade tends to talk about that as though somebody was sloppy. Almost nobody was. Concrete has to be cured, and a sprayed membrane is the cheapest compliant way to do it.

Curing means keeping enough water in the concrete for the cement to keep reacting, and it is part of placing concrete properly rather than an optional extra. ACI 308, the American Concrete Institute guide the industry works to, treats it that way. The alternatives all cost labor: keep the slab wet, or sheet it and tend it for days. One pass with a sprayer needs nobody to come back.

So the person who created your problem was meeting an obligation, on a slab nobody had yet said would be coated, using the option their own economics pointed at. That matters because it decides who you talk to and how. Treating the film as a mistake gets you an argument. Treating it as a decision made without the information gets you a different decision next time.

The word that matters is seal, not cure

Two different specifications sit behind two products that look identical in a drum, and the difference between them decides whether your first pass takes an hour longer or most of a day.

Curing compound

Specification: ASTM C309
What it is for: Hold water in while the concrete gains strength.
Afterward: Its job is finished. Nothing about it is meant to be permanent.
What that means for you: You are removing something that was always going to be temporary. Still a removal pass, but it is not fighting you.

Cure and seal

Specification: ASTM C1315
What it is for: The same, plus stay on the floor afterward as a sealer.
Afterward: It is supposed to still be there. Gloss and durability are part of what it was bought for.
What that means for you: You are removing something engineered to resist exactly that. Same method, materially more of it.

ASTM C309 covers liquid membrane-forming compounds for curing concrete. ASTM C1315 covers liquid membrane-forming compounds with special properties for curing and sealing, adding requirements around things like gloss and durability, precisely because the product is meant to remain.

That is what the word seal is telling you: somebody bought a product engineered to be permanent. It is still coming off before you coat. You are simply removing something built to resist being removed, rather than something that was always going to be temporary. So the useful question on site is not whether there is a curing compound. It is which of the two was used, and the answer is a product name rather than a category.

The conversation that prevents all of it

Every other page in this cluster starts from a slab that already has a film on it. This is the one moment where that is still avoidable, and it costs nothing to anybody if it happens early.

Name a curing method you can live with. Wet curing or sheet curing leaves nothing behind at all. If a membrane is going to be used, ask for a curing compound rather than a cure and seal, so that what you eventually remove was at least intended to be temporary.
Get the product name recorded against the pour. The actual product, in writing, not the category. A data sheet answers questions months later that nobody on site will remember, and the crew that placed the floor almost never records this unless asked.
Require stated compatibility with a subsequent coating. Ask that the manufacturer states the product is compatible with a coating applied later. Plenty are not, and the ones that are not do not say so on the drum.

Raised before the pour, none of that costs the concrete contractor anything. Raised afterward, all of it becomes a variation, an argument, or quietly your problem. If you are being brought into a project early enough to be asked for a budget price, you are early enough to ask these three questions, and they are worth more than the budget price is.

When you arrive after the fact, which is most of the time

The normal case is that nobody knows what was applied. That is not bad luck, it is the default, so it is worth building for rather than chasing.

When there is no record, stop trying to identify the product and start testing the slab in front of you. Whether there is a film, and which of the four kinds it is, is answerable on site in a few minutes, and coverage is almost never uniform, so the answer is a map rather than a yes or no. Then what it takes to get off follows from which kind you found.

Two things are worth carrying into the quote whatever you find. A slab with an unknown treatment is not the same job as a bare slab, and saying so in writing is cheaper than absorbing it. And the moisture question reopens the moment the film comes off, because that film has been holding water in for as long as it has been there, so the reading that matters is the one taken after prep rather than before it.

What this page deliberately does not contain

It covers where the film came from and how to stop the next one. Finding and removing the one in front of you are each a full page already, and repeating them here would leave two copies to keep in step.

How to tell whether a slab is treated, the four things that get called sealed, and why one floor is rarely one surface, is how to tell if concrete is sealed.
What removal actually involves, including why waiting for a dissipating compound gives you a floor that is clean where you would test it and sealed where you would not, is removing sealers and curing compounds.
Why holding water in is the correct treatment for curing, and why that is exactly what makes the film a problem for the coating that follows, is concrete curing vs drying.
No product names and no brands appear here. The two specifications are named so you can ask a precise question. Which products meet them is a question for the manufacturer data sheet of whatever was actually used.