How long the room is out of use

The schedule, hour by hour

The rows below are the same job at your slab temperature. Note where the long gaps are: between coats and after the final one, not during the work.

The clock that starts before the one on this page

The schedule above assumes the slab is ready to be coated. On a new pour it may not be, and that wait is measured in months rather than hours. The federal painting specification UFGS 09 90 00 puts a minimum on it, and the minimum it gives a slab on grade is not the one it gives a wall.

Curing: Allow concrete, stucco and masonry surfaces to cure at least 30 days before painting, and concrete slab on grade to cure at least 90 days before painting.

What that changes for your floor One sentence gives concrete, stucco and masonry thirty days and a slab on grade 90. The specification gives no reason for the difference; ours is that a slab on grade can dry only upward. On a slab poured less than 90 days ago, the schedule above starts when that minimum is reached, unless the product's data sheet and a quantified moisture test say otherwise.

Two limits on that rule are worth stating plainly. It is a construction specification written for federal work rather than a product instruction, so it does not know your resin and cannot override a data sheet that asks for longer. And it is a minimum age, not a measurement: a slab older than 90 days can still fail a quantified moisture test, which is what the moisture page is for.

Some moisture-mitigation products are sold for coating slabs that have not dried out. Where one is specified, its own data sheet sets the requirement. Paying for mitigation to save weeks of waiting is a trade with a price, and it belongs in the installed cost rather than in this schedule.

The temperature rule, stated plainly because it is an approximation

This page stretches each published window by a factor of two for each 18 Fahrenheit degrees your slab is below the data sheet's reference temperature, and shrinks it by the same factor when the slab is warmer. At the settings above the multiplier is 2.08.

That eighteen-degree figure is the Fahrenheit form of the ten-degree-Celsius reaction-rate rule of thumb. It is a rough approximation for a resin system and it is not your product's chemistry; it is our assumption. If your data sheet publishes a second temperature column, use that instead of this.

The recoat window is the thing that catches people out

A data sheet that publishes a recoat window gives two times. Before the earliest, the previous coat is still soft. After the latest, the previous coat has cured far enough that the data sheet may require it to be abraded before the next coat, turning a second coat into a second preparation.

In this model a cold slab stretches both ends by the same multiplier, so the window starts later and also widens, and a two-coat job planned for one day can run into the next. The gap between the two times is 24.9 hours at these settings.

What cold can do, beyond making you wait

• Thicker, colder material levels less readily, so roller marks can stay in the film.
• Check your product's data sheet for a minimum application temperature. This tool flags a slab below 55 F as a prompt to check it.
• A slab colder than the dew point of the air above it collects condensation on its surface, and a wet surface is a poor surface to bond to.
• Heating a room warms the air faster than it warms the slab, so an air thermometer can read warm while the concrete is still cold.

If you have to work cold, warm the slab ahead of time rather than heating the air on the morning, and check the concrete with an infrared thermometer rather than trusting the room.

Consequences of working at this temperature