Epoxy cure time before painting?

best guess 24hrs

I always peelply which leaves a ready to paint surface.

As soon as its hard enuff to sand well without clogging the paper or rolling into small balls shs good to go.

Sand well to lose the wax coating crap that cures on top. Hence the peelply which removes
all that when u pull it off. I use peel ply even on good size glue joint.

So when it comes to West System epoxy, the cure time can vary depending on things like temperature and humidity. Generally, it's a good idea to give it at least 24 hours to fully cure before you start sanding or painting over it.

But keep in mind that the curing process is pretty complex and can be affected by lots of different factors, like the specific West System epoxy product you're using. So to be on the safe side, it's always a good idea to check the product datasheet or manufacturer's guidelines for the most accurate cure times and other important info.

Oh, and if you're planning to paint over the epoxy, it's super important to make sure the surface is properly prepped so the paint will stick well. This might mean using a surface prep solution or doing some sanding to get rid of any leftover debris.

This site has a list of cure times based on the hardener of choice.  www.westsystem.com/hardener-selection-guide/

Hope that helps!

What are you making? 

WTF!.... I worked  with West for decades.

It is solvent free, amine free, and does not wax up.

Thumb print test is best ( tells you that cross linking has occurred 100%) . Then immediately epoxy undercoat to get chemical bond. Allowing to fully cure then sanding/cleaning is inferior and why Sand a epoxy resin and possibly the glass when sanding a undercoat is easier.

Extra sanding introduces extra time, contamination...

I used to train the pro's on the efficiencies and economics of systems and they never Sand a resin.

Peel ply and infusion methods are different scenarios for another day

www.westsystem.com/105-epoxy-resin/

When expoy has cured the chances there is some Amine blush is near inevitable. You need to remove that and any gloss if you want a well bonded long term finish.

You can wash the blush off with water and scouring pad like a scothbrite or similar. Rub it dry immediately or it resettles on the surface.

The best way to remove the gloss is sanding.

Hence I like peel ply, it removes that clean up/prep.

If you are using 105 with 205 or 206 and it's not ready to to go after 24hrs you have been visited by Mr Cock Up.

The paint chemists and I did a lot of test panels prior to using it on the boats. Cleaning and sanding the expoy was a must. The paint would just not sit on vertical unpreped surfaces, gravity won everytime.

You want to be a little cautious about expoxy over cured expoy as well. That blush can be a right bitch.

I leave it for at least a couple of months to go a nice yellow colour before sanding and painting