OP
OP
Drilling/grinding fiberglass/epoxy
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OP
OP
Lou_tribal
Guru
A lot of people are referring to boatworks videos, I need to take the time to watch them.
Thank you!
L
I don't know that I would gelcoat an entire boat over epoxy (but then I wouldn't gelcoat an entire boat after the build anyway - I'd Awlgrip or similar).
However for smaller areas it seems to work fine.
Here is WEST Systems take on it:
https://www.epoxyworks.com/index.php/applying-polyester-gelcoat-over-epoxy/
For myself, here is my experience:
1) I made sure not to have a hardener rich epoxy mix (in other words, either mix it perfectly, or err on the side of resin). As I understand it, it's the amines in hardener that can cause a problem and if there is extra hardener "free" to roam around with no resin to combine with, then problems can ensue.
2) Let the epoxy cure thoroughy (I waited a week or so, which was no problem as I was doing other things simultaneously; it might not need to be that long). Wash off any amine blush (happens in cooler/damper environments; you remove it with just plain water and a 3M pad so not difficult).
3) If you use fairing compound, then go back and re-coat with plain, unfilled epoxy.
After the above I gelcoated over two or three repairs with zero problems. The largest was about 10" in diameter.
Reason I note step 3 is that even though it's called out to do that, on my first larger patch I skipped that step (my bad). Sure enough, what happened was the gelcoat cured great on the places where I had not faired, but didn't harden on the areas with exposed fairing compound (System Three Quickfair). I wiped it off with acetone, re-faired, painted over it with plain epoxy (basically what I should have done in the first place) and then no further problems. Won't be making that mistake again.
I can see why boatyard personnel would eschew this method, as they need to get the job done, and going to each boat for another step day after day gets expensive for the customer and is piddly for the crew.
However for a DIY-er who has a few irons in the fire anyway (other boat jobs, other life things), it may not be any hardship. For me it was just the first thing I did each day arriving at the boat, so the fact that I spread it out over a week was of no consequence. I am used to working with epoxy, have it on hand, and don't like the smell of "esters."
Not saying everyone should choose to do it this way, but I often hear you can't gelcoat over epoxy as a blanket statement, so I wanted to note that you can, if the situation works for you (and it may work for many DIY-ers). And with the WEST article I linked above, you don't need to just take my one word for it.
FF
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" I made sure not to have a hardener rich epoxy mix (in other words, either mix it perfectly, or err on the side of resin). As I understand it, it's the amines in hardener that can cause a problem and if there is extra hardener "free" to roam around with no resin to combine with, then problems can ensue"
This not my understanding of how epoxy hardening works .
On polly resin the hardener mixes in and becomes part of the cured resin.
On epoxy the hardener causes the resin to cure , but does not become part of the resin. The mfg recommended hardener gives the best results
The amines form on the surface and can simply be scrubbed off with dish washing soap.
*******
A tip for those beginning to work with GRP , the dust is horrible , so before starting grinding use talc powder on all exposed skin , and to clean up use cold water, it closes your skin pores and makes scrubbing the Glass dust off easier.
This not my understanding of how epoxy hardening works .
On polly resin the hardener mixes in and becomes part of the cured resin.
On epoxy the hardener causes the resin to cure , but does not become part of the resin. The mfg recommended hardener gives the best results
The amines form on the surface and can simply be scrubbed off with dish washing soap.
*******
A tip for those beginning to work with GRP , the dust is horrible , so before starting grinding use talc powder on all exposed skin , and to clean up use cold water, it closes your skin pores and makes scrubbing the Glass dust off easier.
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Well maybe I misunderstood the folks at WEST I spoke with. They mentioned to make absolutely sure not to have "extra" hardener in the mix (so mix perfectly or err on the side of resin rich).
I believe I remember them saying the same thing for coating water tanks (not saying I'd recommend that). Basically, make it resin rich so there is no hardener left with nowhere to bind.
I had another situation some years ago where I accidentally mixed a batch of epoxy with too much resin. Rookie mistake: I used some pigment to make it a bit whiter, and neglected to notice that counts as resin, so I still used the "correct" amount of resin, thus ended up resin rich.
When it hadn't hardened in a week, I called WEST. They said they were 99% sure it would harden and be fine. I was still not too confident, so I scraped it all off and started over. However, I had saved my mixing cup with the same batch in it, and sure enough a week or so later it was hard as a rock.
On the other hand, they said, if you mix up a batch that is hardener rich, it will never ever cure. It will cure to the texture of super hard cheese and then stop.
But I take your point in that maybe I mis-spoke about the technical terms or chemical process. That was my understanding of it as a layperson.
Regardless, you can gelcoat over epoxy as outlined in the WEST article. Still, I would never fully gelcoat an already built boat as a new coating - I would use Awlgrip or similar. But I was doing a repair on a boat that had been gelcoated in the mold and was still sporting its gelcoat finish. (I actually hate working with gelcoat but in this case I had to. I did kick and scream but then went ahead.)
I believe I remember them saying the same thing for coating water tanks (not saying I'd recommend that). Basically, make it resin rich so there is no hardener left with nowhere to bind.
I had another situation some years ago where I accidentally mixed a batch of epoxy with too much resin. Rookie mistake: I used some pigment to make it a bit whiter, and neglected to notice that counts as resin, so I still used the "correct" amount of resin, thus ended up resin rich.
When it hadn't hardened in a week, I called WEST. They said they were 99% sure it would harden and be fine. I was still not too confident, so I scraped it all off and started over. However, I had saved my mixing cup with the same batch in it, and sure enough a week or so later it was hard as a rock.
On the other hand, they said, if you mix up a batch that is hardener rich, it will never ever cure. It will cure to the texture of super hard cheese and then stop.
But I take your point in that maybe I mis-spoke about the technical terms or chemical process. That was my understanding of it as a layperson.
Regardless, you can gelcoat over epoxy as outlined in the WEST article. Still, I would never fully gelcoat an already built boat as a new coating - I would use Awlgrip or similar. But I was doing a repair on a boat that had been gelcoated in the mold and was still sporting its gelcoat finish. (I actually hate working with gelcoat but in this case I had to. I did kick and scream but then went ahead.)
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