Epoxy fade

Hi all,

I used a carbon tape to join the deck with the hull of a kayak (see attached picture) with epoxy measured very carefully. I add a little bit of Silica in the first (bottom) layer then added the tape and then more epoxy on top of it. After 3 days I took the kayak out in the water for a test as this is a prototype.
Once I return after a few hours I noticed that nearly the whole tape/seam took a fade/grey color, I don't know how to describe it properly but you can see in the picture.
The small part of the tape that is black in the picture is how it should be/was before it had it's first touch with the salty water. It looks like the epoxy wasn't cured and went somehow inside or what?
I honestly have no clue what happened as the epoxy I'm using needs 12 hours to cure and I left it 3 days anyway.

Any ideas?

 

It looks like there's quite a bit of air in the laminate, plus epoxy weather's poorly, so discoloring after UV exposure is normal.

 

@ondarvr thank you. There isn't any air in the laminate; maybe it looks like that because of the color it gets after adding aerosil plus I didn't clean the seam after the trip.
Also is not the UV exposure but the salty water and only on this kayak. I've used the same epoxy to cover tapes as keel strip in many other kayaks with no discoloring at all and they are months under the sun.
Any other ideas?

 

I guess the easiest is to sand it and add some clear gelcoat or gelcoat anyways to solve it.
The problem is that I can't find clear gelcoat locally.
Any ideas of what I can use to protect the epoxy but still be visible like it is now ofcourse without the discolor?

 

Transparent paint, aka. clearcoat, laquer. If your local marine paint supplier doesn't have it in stock, a high quality automotive one is also an option, and that should really be available everywhere.

 

Optically transparent Epoxy is a specialised product, and normally you would expect some colour variation unless you paid for the premium product.

To properly cure Epoxy, its not just time that is required. but also temperature (not UV).
Do a small test patch on something, and cure it in a hot box with an incandescent lamp for 24 hours, to see if that helps. I expect not.

You may find the Epoxy manufacturer has a recommended cure plan.

Some more ideas here

 

If what looks like air in some locations in the fabric is just thick and discolored epoxy, then it would lead me to look at the silica.

Silica can take on moisture from humidity, which may cause some discoloration of the epoxy when warmed in the sun.

 

Why clear? If you want it black, try a two part epoxy paint. Unless, there is a concern that there is more wrong with the epoxy strip than just fading color. Are you concerned or might be weaker than it should be?

 

It looks like the aerosil isn't evenly dispersed and I would suggest that it is the presence of the aerosil that is at the root of the opaque appearance.Applying a clear coat won't make any difference to this and if appearance matters to any extent,I would suggest a coat of black tinted epoxy,followed by the clear coat that others have advised.

 

When I was making SUP's, I tried to avoid clear coating carbon fiber (was used in standing area for stiffness) to avoid a temp rise with the black that could melt the EPS foam underneath and take the epoxy past its glass transition temp. Most often I would use an opaque tint in the epoxy like white or light blue.

PS and then there would be EVA foam on top of that.

 

Looks like chalk out to me. If it is chalky; it'd sand out, but you need uv protection.

Bloom is also chalky. If it is greasy; maybe blush.

Either way, I'd first wash with warm water and Dawn. Then follow with sanding. Use 220 and go up or down from there as needed. Then apply UV coating. Same course if the silica took on moisture. The final coating should not contain silica or really epoxy either.

good read on blush and bloom; even if it was just high sun coming off the water and sky

https://www.tri-iso.com/documents/Epoxy_Amine _Blush_Prevention.pdf

 

I suspect there isn't anything really wrong and that you played with it a little too much and worked some of the amine blush back into the goo. Did you go back around it and try to fill in the weave as it was getting a bit chewy in the pot?

Amine Blushing and Blooming of Epoxy Binder Systems in Protective Coatings https://www.pcimag.com/articles/85460-amine-blushing-and-blooming-of-epoxy-binder-systems-in-protective-coatings

Cross-posted with fallguy, but different links at least.