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Hello everyone,
I already asked this on Facebook, but it doesn't seem to be a problem lots of people encounter:
I’m building a Kaholo and I’m having a very unsatisfying experience with the process of coating the fiberglass with epoxy.
I wasn’t able to do all the coats while the former was not fully cured, so the supposed last coat went on fully cured epoxy that I had sanded with 120 grit with a random orbital sander.
Than I intended to give the hull a good sanding before putting primer on, but on places where there was a high spot and thus I sanded through the last coat of epoxy, it began peeling away in flakes, like sunburned skin. It sees that the epoxy just didn’t adhere to the coat below.
I’m not aware where I possibly did something wrong and the supplier of the epoxy (Berger-Boote) is sure it wasn’t faulty.
Did this ever happen to anyone else?
I was told it could be amine blush, even though the epoxy's not supposed to blush, but I made different samples, cleaning the first coat with water, with alcohol, with both or with nothing, and the problem occurred in all of them.
The shop environment isn't particularly humid or cold.
Any ideas?
4 replies:
RE: peeling epoxy
Hi hspira,
all samples were sanded, the ones I washed with water after washing and drying.
RE: peeling epoxy
Hi Dagi,
thanks for the additional information.
i have to admit, is sounds very strange and tthere is nothing obvious i can think of other than the epoxy itself.
if it's not the epoxy, and you have a clean and sanded surface, the new epoxy coat shouldn't flake off. if it does, then there must be a contaminant on the surface -- amine blush is the typical culprit...but there are others. but usually if there is a contaminant on the surface, your epoxy, when applied, will bead up or form fish-eyes.
can you try with another epoxy? have you called the epoxy manufacturers support line to see if they have any ideas?
coming back to possible contaminants, is there anything releasing grease or soot or oil into the air? when cleaning with alcohol, are you using denatured alchohol? when you dry or clean the surface are you using a clean paper towel and not a cloth that has laundry additives on it? to confirm, is the epoxy you are using to overcoat the same as the epoxy that you used on the undercoat?
i am shooting a bit in the dark....but just kind of going through my checklist of things that can cause bad adhesion of an overcoat of epoxy on an existing coat.
h
RE: peeling epoxy
Thanks h.
I'm racking my brain for a while now, but I can't think of what could have compromised the surface. No oil or anything in the environment. The cloth I used to wipe with was an old T-Shirt, just regularly washed, no softener or anything. Anyway it happened as well with the sample I didnt wipe with anything.
That's how I found out, it wasn't the alcohol, as I suspected in the first place (because it's only 38% cleaning alcohol)
I didn't sand as long as before varnishing, but a few passes with the random orbit sander with a new 120 grit disc should make for a sufficiently rough surface to make the epoxy stick I'd think.
The epoxy is from Berger-Boote, the German supplier of CCL kits and it doesn't say who's the manufacturer, but anyway I used only this product.
I talked with the owner on the phone and x mail, and he had consulted the supplier. It seems nobody else ever had this kind of problem.
RE: peeling epoxy
» Submitted by hspira - Wed, 11/6/24 » 11:35 PM
Hi Dagi,
just to confirm, are you saying that even in your experiment where you let the first coat cure completely and washed it .....that the second coat did not adhere to the first coat?
in your samples, did you sand the cured coat before overcoating....or just cleaned it?
if you did not sand it after clearning it, can you do a sample, clean it, then sand the undercoat with 120 grit to scuff it up...then recoat.....and then report your results?
h