Dried lam rails were fine (great). Light sanded up and back (whole board) with #120, air’d off, gave mild wipedown with Trader Joes Citrus Shampoo, rinsed and towel dried. This is what happened. Some places turned almost white!
Why would I get splotches? Went ahead and did a hotcoat and maybe 20% did not turn back into deep red. Some splotches are still there, see pic (before hotcoat).
Not as cured as it probably should have been?
Epoxy lam was cured 24 hrs in warm weather. With hotcoat, it’s not t-h-a-t bad.
Looks like one of two things:
The dreaded amine blush - what kind of epoxy did you use
or
You sanded to long / too hot in those places & remelted the resin. Are those white places (before hotcoating, anyway) a little tacky? Did they gum up your sandpaper?
Some epoxies - we’re back to what kind did you use - do this more than others. West, in particular, in my expeirence. I did a couple repairs on Patagonias several years ago with West epoxy and had to wait a week before sanding wouldn’t produce that white gum…and I think the gum might actually be related to the amine blush. Epoxies with amine-based hardeners behave with this stuff rising to the surface as it cures, kind of like sanding resin with wax. Other epoxies don’t use amines and work differently (better). It actually looks like your red stayed red under those splotches, so I’d bet its a surface cure/sanding problem.
High humidity can do this too. Old epoxy users used to spit in the bucket to intruduce moisture to the mix, but I don’t remember what that supposedly did for them…
gave mild wipedown with Trader Joes Citrus Shampoo, rinsed and towel dried.
theres your problem …
youve just put moisture on what looks like not fully cured resin , the hardener has just sucked the moisture straight in …
a full cure is dependant on having at least 25 celsius for 24 hours …
if the temperature drops below that it will extend the cure time …
never wipe or add anything else …
just a blow with air , a gentle rub with your hand to remove any more dust another blow , then the next coat …
that to me is blatant moisture penetration into uncured resin …
another scenario is your ratio of part a and b was slightly out , being slightly part b rich , leaving excess hardener molecules floating around open to moisture attraction if exposed …
sand it a little deeper , and recoat …
or do a filler coat spray and cover it …
regards
BERT
I’m with Bert on this one. Maybe do a light sand and then repaint the red on the outside, I use Design Master paint from Michaels. Finish with a gloss or a spray finish/sealer.