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document updated a month ago, on Feb 3, 2023

what does "cure time" mean for adhesives?

In the process of writing this webpage, I was trying to compare the quoted cure times from various different glues.

My conclusion? It seems difficult to make an apples-to-apples comparison between different glues, because the published cure time is dictated as much by the marketing department as by the engineering department.

some concrete examples

Here's what I mean:

DAP's RapidFuse Instant Adhesive claims to "cure in just 30 minutes". I'm skeptical of that because almost no glues cure that quickly, not even contact cement or cyanoacrylate glue (CA glues are usually quoted as curing in 8 to 24 hours). Note that RapidFuse is a special type of cyanoacrylate glue. But the back of the package does go on to clarify a few things:

In this case, saying "can be unclamped after 30 minutes" might be a more accurate statement.

DAP WoodWeld contact cement says it "bonds permanently when sufficient pressure is applied, and reaches maximum holding strength in 7 days." And here I think we get to the crux of the issue — contact cements have to finish ~95% of their curing by the time that pressure is applied, because once the laminate or tile flooring is laid down on top of the contact cement, there is extremely little opportunity for off-gassing any more.

But I could see how a company would want to claim a "20 minute cure time", because that's when ~95% of the curing is complete, and very little curing takes place in the 7 days after that. But for apples-to-apples comparisons, it might be good to use more precise terms instead, like "maximum strength is achieved in..." or "clamps can be removed after..." or "item can be jostled, sanded/sawed, or used normally after ...".

From a scientific standpoint, I don't know if there's any way of quantifying what percentage of the adhesive has chemically cured, since drying (detectable via mass loss) isn't an accurate way to gauge curing progression.