Time between coats and clear with Silmar 249

General Composites Discussions Composites Talk
#1

If I am using Silmar 249 with MEKP, how long should I wait between applying coats of resin to a part? I am making a set of overlay mirror covers for my truck.

Here are the steps I think I should follow:
-Sand the mirror caps with 80 grit,
-Tape the underside off to prevent resin runs,
-Add resin (no wax) to sanded surface and wait until it’s tacky,
-Stick CF onto tacky resin and use a paintbrush to push it smooth,
-trim edges of CF cloth
-add several coats of resin (wax in last one)
-sand smooth and decide if I need more coats of resin
-once happy with the thickness sand smooth and clear coat

My two biggest questions are with the Silmar 249…
how long should I wait after painting resin on should I wait to paint more on? (Time between resin coats?)
How long after the last coat with wax and wet sand should I wait to clear coat?

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#2

I think my rule was to wait a few hours until it was almost fully cured or past the exotherm state. Maybe a few hours.

Before clearing I let my part sit in the sun for a good full day for things to shrink up nicely. Even before sanding that is. After sanding you’re good to clear. But I’m just a hobbyist so maybe the pros can chime in.

#3

I don’t know the specific resin, but generally any polyester or vinyl ester resin is best recoated just prior to tack-free. So when you can touch the surface and it feels a bit sticky and you leave a fingerprint, but you don’t get any resin or residue on your finger.

As for how long before clear coating, I’d say 24 hours at room temperature. If you can do an elevated temperature cure then this is ideal, but for a skinned part this isn’t so important.

#4

Thanks for the help guys. I’m a hobbyist too. I’ve been making parts for a little over a year and just wanted to see if I’m on track. I’ll post a couple of pics.

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#5

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