Induction Time
A deliberate pause between mixing a product and applying it, called for by some data sheets so the reaction can get properly underway before the material goes down. Also called sweat-in time, and it is subtracted from your working window rather than added to it.
What the wait is for
Some data sheets ask you to combine the two parts, stir them, and then leave the pail alone for a stated period before any of it reaches the floor. That period is the induction time, sometimes called sweat-in time.
Its purpose is to let the reaction get properly started while the material is still gathered in one mass. Held together in a pail the components stay in close contact and the reaction initiates evenly through the batch. Spread thin on a cold slab the same material loses heat quickly, and some chemistries struggle to get going at all under those conditions. The wait is the manufacturer buying the reaction a head start somewhere more favorable than your floor.
Two reasons to let a pail stand, and only one of them is this
Standing a mix also lets entrained air rise out of it, which is a genuine benefit and worth taking on anything that has been stirred hard. Our page on a cloudy or milky clear coat covers that case, where air whipped in at the mixer ends up trapped in the film.
But that is deaeration, not induction, and the two are worth keeping apart even though the action on site is identical. A product with no specified induction time still benefits from a moment standing for the air. A product that does specify one needs it for the chemistry, whether or not any air went in. Knowing which you are doing tells you whether the sheet sets the length or your judgment does.
It is taken out of your working time, not added to it
This is the part that catches people, and it is worth being blunt about. The clock on mixed material started when the two parts met, not when you picked up a squeegee. An induction period is spent from the same window as everything else.
So the working time you actually have is the pot life minus the induction. On a slow product in mild conditions that difference is comfortably absorbed. On a fast product on a warm day it can be a large fraction of the window, and it is the batch size that has to give. Check the pot life for the conditions you are in and subtract before deciding how much to mix, rather than planning against the figure printed on the sheet and discovering the shortfall with a full pail.
When there is no induction time on the sheet
Then there is not one. Most floor coatings do not call for an induction period, and inventing a wait the product does not need burns working time that could have gone into laying material. It is not a free precaution, because it is subtracted from the same window as before.
A short stand to let air out remains reasonable, but recognize it for what it is: a judgment about air, measured in a minute or so, rather than a chemistry step measured off a document.
One last caution. Like every other timing figure on a sheet, an induction period is quoted at a reference temperature. A cold day slows the reaction the induction exists to establish, and lengthens the pot life it is being taken from, so the two move together. Check both for the day rather than adjusting one and assuming the other stood still. No specimen figure is given on this page, because induction times are short, product specific, and there is no typical one worth printing.
Frequently Asked Questions
What is the wait actually for?
To let the reaction between the two components get properly started before the material is spread out. Mixed and left in the pail, the components stay in close contact and the reaction initiates evenly through the whole batch.
Some chemistries develop their properties poorly if that does not happen, because a thin film spread on a cold slab loses heat quickly and the reaction can struggle to get going. The wait is the manufacturer buying the reaction a head start under better conditions than the floor provides.
Is it the same as letting the air out of a mix?
They are two different reasons to let a pail stand, and they get run together on site because the action is identical.
Standing does allow entrained air to rise and release, which is a genuine benefit and worth taking on any product that has been mixed vigorously. But that is deaeration, not induction. A product with no specified induction time can still benefit from a minute of standing for air, and a product that does specify one needs it for the chemistry whether or not any air was whipped in.
Does the induction time come out of my pot life?
Yes, and this is the part that catches people. The clock on the mixed material started when the two parts met, not when you began spreading. A five minute induction on a product with a short pot life is five minutes of that window gone before anything reaches the floor.
So the working time you actually have is the pot life minus the induction, and on a fast product in warm conditions that difference decides your batch size. Plan the batch around what is left, not around the figure printed next to pot life.
What if the sheet does not mention one?
Then do not invent one. Most floor coatings do not call for an induction period, and adding a wait the product does not need simply burns working time you could have spent laying material.
A short stand to let air release is a different matter and is usually harmless, but that is a judgment about air, measured in a minute or so, rather than a chemistry step measured off a sheet.
Does temperature change it?
It changes everything else about the cure, so treat the induction figure the same way: a number quoted at a reference temperature rather than a constant.
A cold day slows the reaction the induction is meant to establish, and it also lengthens the pot life the induction is being taken from. The safest reading is that the two move together, so check both for the conditions you are in rather than adjusting one and assuming the other held still.