Is sandable epoxy cured epoxy?

S

strum456

Oldtimer
In the winter time, if I spray epoxy at 67 to 70 degrees metal temp, it takes a minimum of two days before it can be sanded. Yesterday I sprayed two coats and put the car in the sun for four or five hours. It wasn't even a hot day. I measured the metal temp at 100 to 110 when the sun was not covered by clouds. I pulled the car inside and let it cool for a while, then started sanding. The epoxy just turned to dust!

So, my question is, how cured does epoxy have to be to sand that well? If I can sand it that easiily, should I scuff it before filler, even though it is less than a day old?
 
i always scuff with a red scotchbrite. even if working over it the next day. By doing that...it keeps me from asking should or or shouldn't i? doesn't take much longer to scuff the panel up real good and i dont have to worry about it. just extra insurance.
 
I use this basic rule when trying to determine if a scuff is needed: if I can scratch the epoxy by rubbing my fingernail over it then there's no need for scuffing before filler-it's usually this way for a few days. I have never ever had any adhesion problems. You can do yourself a favor and do an easy test: the next time you shoot some epoxy spray a piece of scrap steel, put a dab of filler on it the next day, then another the following day, and again for 5 more days also checking the epoxy hardness each day-you'll see the difference. Then let it set for another week and do a bend test to see at what age and epoxy hardness the filler adhesion is compromised. In reality this will only take minutes of your time but it'll provide a great deal of experience or feel for how the products work together-just a suggestion.
 
Like Jeremy, I have been just scuffing it so I don't have to worry. I do the fingernail test too. When you can't scratch it with your nail is when it is sandable. So, is it 100% cured and all done shrinking at this point, even if it is only 4 hours old or so?
 
Latley, I have been using epoxy for all of my blocking. With the summer heat, I absolutely love it. I am trying to understand what the limitations are.

Here is an example: Everyone I have talked to says to wait a day before putting filler over 2 coats of epoxy. If I can sand it easily after 5 hours in the sun, wouldn't that mean that it is cured well enough to put filler over it? From what I have seen, heat or uv light make more of a difference than time. So, would it be more appropriate to judge the cure of epoxy by how it sands or the finger nail test rather than time?
 
I wait overnight with two coats of epoxy but if it's sanding well then I bet you're OK, worst that could happen is the cure of the epoxy under the filler will be delayed if it soaks up enough solvent from the filler-JMO
 
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