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I picked up a can of Adhesion Promoter from Halfords.

The directions say to apply two coats waiting 10-15 minutes between each, then allow to dry for at least one hour before applying primer/lacquer.

When I googled I saw that some adhesion promoters require you to spray within 10 minutes of applying the final coat. However my can does not say this.

I am wondering if it's OK to spray the adhesion promoter and leave it and come back to it the next day to spray, or if it's very important to do it after the indicated time frame, or if it doesn't matter at all.

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  • Welcome to Motor Vehicle Maintenance & Repair!
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Jul 17, 2021 at 22:44

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Bottom line: Follow the directions.

Basically, you need there to be tack on what you just sprayed in order for the next layer to grab hold of it and not come off. If you leave it until the next day, everything has dried up and there's nothing much for the next coat to grab hold of. Regular painting requires you to scuff up the surface first prior to throwing paint on there. If you don't, there's no mechanical bond to hold the paint in place. It's the same principle here.

If you don't have time to do the job, wait until you do. You'll get the best, long lasting results by doing so.

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  • Sort of makes sense, but at the same time when you sand something you can wait as long as you like before painting it because the surface is good for adhesion. I wasn't sure if this basically dried into a nicely 'sandpapered' coating that will adhere to, or if the adherence specifically requires it to be slightly damp. Plus it says 'at least an hour'... I suppose the best course of action is to spray 2 coats, wait an hour, and then get to work
    – NibblyPig
    Jul 17, 2021 at 22:57
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    There's two different mechanical bonds going on here. With Sand paper, you're creating a rough surface. With not letting it dry completely, you are allowing the two materials to mix slightly, which causes mechanical adhesion. If the product you're using states to only wait a few minutes or an hour, its' best to do that. Waiting overnight will most likely cause you issues which may not present itself right away, but will eventually.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Jul 17, 2021 at 22:59

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