Barrier coat disaster

  • Thread starter Thread starter kko
  • Start date Start date
Not an expert, so please someone tell me why I'm wrong, but surely the first layer of epoxy never actually cured?

Top google hit for "how long for epoxy to cure":

With two pack epoxies, where the curing mechanism is an internal chemical reaction, full cure could take months. During the curing process, there are many chemicals reacting with each other to form a highly cross linked network, turning liquid into solid. This slowly makes it harder for any remaining non-cross linked parts to react. The temperature and humidity during the curing process plays an important role in the speed of cure, as warmth provides the system with more energy to react. So this means the curing process is faster in warm temperatures, and slower when it’s cold.​

…​

In reality, full cure is usually defined as the time it takes for the product to meet all of its required end use properties. This is usually around 7 – 30 days depending on the temperature during cure.​

Epoxy based products may appear to be cured ie they are dry on the surface, but they may not have reacted fully throughout the paint film.​

Therefore it is important that the recommended over coating times are followed to avoid a partially cured product from absorbing solvent from the subsequently applied coatings leading to potential problems such as but not limited to blistering or poor adhesion.​

link​

So if you're using thickened epoxy to fill a hole or glue something (is this called "filleting"?) then we tend to think of it as "done" or "set" when the epoxy is hard after 24 hours, but it's not really cured.

So OP painted on the first coat, after 24 hours it was hard, but it still wasn't fully chemically cured - it was prevented from curing by the addition of extra layers on top which isolated it from the atmosphere.
 
We didn't use acetone after final sanding. This is another issue that we think of, but just another of many. It was not in the instruction after final sanding.

No other chemistry was used at all.

There are some places where adhesion is better and regions where there is almost none. I just don't want to scratch it all now to find how much is good/bad.

We did the final sanding with 40 and 60 grit. Perhaps the sandpaper could be clogged sometimes and make some polish. But generally discs were replaced when clogged. In some places there are visible markings of sanding under the fallimg epoxy.

I didn't contact the manufacturer yet, but it does not look like the epoxy problem. Just some problem of many possible and not easy to figure out which one actually.
 
The Coppercoat was applied 9 days after the barrier coat. Barrier was applied wet on wet and there is no problem with the epoxy layers separation.
 
Two different products in use and two different application requirements.
If I remember correctly West has an overcoating time of around 24 hours for a chemical bond, which is why I applied one coat per day. Coppercoat however requires a 'wet on wet' continuous process, round and round the boat with thin coats until all the material has been applied.

If I have read correctly it seems that you applied West 'wet on wet'. If this is so then @KompetentKrew may well have hit on the reason, the thick multi layer West epoxy coating has not fully cured due to a build up of solvents within it. Depending on the time lapse between applying the West and the Coppercoat those solvents may have been prevented from escaping by the water based Coppercoat.
 
According to not enough drying after washing, could be also a reason. But why no adhesion on the old gelcoat, where water couldn't penetrate deeply, like it could into the fiberglass? Some areas of better adhesion are just on the fiberglass on the bottom, where drying must have been slower than near the waterline on the gelcoat. But some weak areas also there.
 
West System was applied "wet on wet" in sense that the previous layers were still tacky, but this is according to the instruction. Also it is supposed to be a solvant free product.

But in fact, better adhesion seems to be in the places where the layer is thinner. But this may be just mechanical strength of the thick layer causing bigger delamination regions when i lever the edge (not using much force).
 
Just another thought on the cure problem. In my experience fully cured West epoxy is hard and brittle but your film was flexible indicating it needed more time to harden.
 
So is this possible that thick layer of West System may not cure? In 9 days before the Coppercoat and 11 days total? I have used extra slow 209 hardener because it is hot here everyday.
 
srm said:
Just another thought on the cure problem. In my experience fully cured West epoxy is hard and brittle but your film was flexible indicating it needed more time to harden.
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but west System specify a time between coats.., they do not say that it needs to be "fully cured"
 
Removed pieces are not much flexible and rather brittle. I can bend them slightly but they break with cracking sound.
 
I even thought that it is too thick and stiff, that is why small scratch can pull bigger region, piece after piece, by delaminating the edge. But in some places adhesion is good enough that I can't scratch pieces bigger than a fingernail size.
 
Laser_310 said:
but west System specify a time between coats.., they do not say that it needs to be "fully cured"
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Indeed; to get a chemical bond the lower coat must still be active. If it does fully cure between coats it has to be abraded to give a mechanical bond.

However, I suspect that adding the barrier powder thickens the coats and slows down the final cure of the coating. I have only used West in the UK with the fast hardener for low temperature applications and there may be differences due to the slow hardener used.

As we seem to have collectively run out of ideas without any clear conclusion I would suggest that @kko asks the West people for their ideas.
 
kko said:
So is this possible that thick layer of West System may not cure? In 9 days before the Coppercoat and 11 days total? I have used extra slow 209 hardener because it is hot here everyday.
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I would think those times were more than adequate, but your experience with sections of coating peeling off when you removed the masking tape indicates otherwise.
The coating will continue to cure which may explain why you are finding differences in adhesion and flexibility.
As mentioned above I think it would be a good idea to contact the West people for their ideas.
 
srm said:
I would think those times were more than adequate, but your experience with sections of coating peeling off when you removed the masking tape indicates otherwise.
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i think it's more likely that the problem was some contaminant on the surface prior to application of the first coat, than that the problem was from incomplete curing.

also - i am pretty sure that west says the stuff can be used for a long time - even after the color changes, which is years

probably the OP bough the stuff for this project, so it was new enough
 
kko said:
We didn't use acetone after final sanding. This is another issue that we think of, but just another of many. It was not in the instruction after final sanding.

No other chemistry was used at all.

There are some places where adhesion is better and regions where there is almost none. I just don't want to scratch it all now to find how much is good/bad.

We did the final sanding with 40 and 60 grit. Perhaps the sandpaper could be clogged sometimes and make some polish. But generally discs were replaced when clogged. In some places there are visible markings of sanding under the fallimg epoxy.

I didn't contact the manufacturer yet, but it does not look like the epoxy problem. Just some problem of many possible and not easy to figure out which one actually.
Click to expand...
That’s good, because degreasing with solvent prior to application of epoxy is known to adversely affect bond.

Mike
 
Yes. The resin was fresh. I will ask West. But I don't suspect the resin. Contaminant could be. But what and why, no idea. There are some splashes of the first layer over the masking tape. Just on the not sanded, not cleaned surface. These seem to have best adhesion :/
 
Laser_310 said:
probably the OP bough the stuff for this project, so it was new enough
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A friend bought a different epoxy product from a local supplier to use on his project. It was a special order so should have been fresh. When he ran into problems applying it he contacted the manufacturer direct - as soon as he gave them the package details he was told not to use it as it was so old the resin would have deteriorated. The local supplier gave my friend a full refund, and was obviously angry with their wholesaler.
 
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kko said:
Yes. The resin was fresh. I will ask West. But I don't suspect the resin. Contaminant could be. But what and why, no idea. There are some splashes of the first layer over the masking tape. Just on the not sanded, not cleaned surface. These seem to have best adhesion :/
Click to expand...
Please let us know what response you get, as it may well help others.
 
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