Industrial two pack epoxy or Gelshield

[Jcorstorphine]

Whilst I was pressure washing the hull last autumn, some large chunks of antifouling and “paint” came away leaving an abraded gel coat. It would appear that one the previous owners had the entire hull painted with conventional gloss paint. The bare area is about a square metre but the fibreglass is in good condition with no signs of blistering, the hull is about 35 years old.

I have a quantity of Industrial two pack epoxy paint which is still within its use by date. The paint is used to seal the internals of steel vessels to prevent rusting and I was wondering if I could use this on my hull rather than Internationals GelShield concoction.

Any comments about using this industrial two pack epoxy would as ever be most welcome.

 

[Seajet]

The whole point of gelshield is that it's solvent free.

In the early days of osmosis treatment / precautionary coatings, epoxy such as International 709 was used.

Then it was discovered that the solvents in these epoxies can actually promote osmosis !

So solvent free Gelshield and its' competitors were developed.

It sounds like your handy epoxy may not be a good idea...

 

[Jcorstorphine]

Thought that a bit of solvent would be a good thing

The whole point of gelshield is that it's solvent free.

In the early days of osmosis treatment / precautionary coatings, epoxy such as International 709 was used.

Then it was discovered that the solvents in these epoxies can actually promote osmosis !

So solvent free Gelshield and its' competitors were developed.

It sounds like your handy epoxy may not be a good idea...

I have heard that about being solvent free but you would think that a bit of solvent would help the epoxy to bond to the polyester. Seem to remember that when building my previous / previous boat, I always cleaned the surface of the hull interior with acetone before applying layers of polyester when fitting bulkheads and engine beds but then that was polyester on polyester on layup rather than gelcoat.

 

[Plevier]

Gelshield Plus is solvent free but that is for building up after peeling isn't it? You'll be comparing with Gelshield 200 which is not solvent free.
If I were in your shoes I would use the stuff you've got - but I'm not a chemist.
If I wanted to buy marine high build epoxy primer - not solvent free - I'd get Jotun from Shepherd Marine a lot cheaper.
In fact here's information quoted from Malcolm at Shepherd (I've no connection just a customer):

Gelshield 200, which is the International equivalent of Jotun Penguard HB is only 45% volume solids as opposed to 54% for Penguard! Only Gelshield Plus, the gelcoat replacement, is solvent free.
The thing about solvent free primer being required for waterproofing/osmosis protection is a complete myth. There is a risk when using solvented products of getting solvent trapped in the paint, which subsequently become pinholes. This only happens if you apply successive coats before the previous coat is “through dry” (i.e. all the solvent has evaporated) or you continue to apply the paint when it is past its mixed “pot life”. Some people even try to extend the pot life by adding thinners, which is asking for trouble. The other thing people aren’t aware of is that if you use solvented products, you need more coats. In the case of Gelshield 200, the dry film thickness is only 45% of the wet film thickness, so you need more than twice as many coats to achieve a given dry film thickness than if you’re using solvent free products. This isn’t fully appreciated, so often there isn’t a high enough overall DFT applied of solvented products to give good protection.

 

[rob2]

Yes, when bonding in a bulkhead or similar on a previously uncleaned polyester layup it is necessary to use acetone to remove the amine blush from the surface or you will not make either a chemical or mechanical bond. Even with Gelshield, unless you're sure the surface is clean, it's advisable to wash with acetone. But a wipe on and wipe off will all evaporate without having time to soften the gelcoat.

As to the possibility of a solvent based epoxy promoting osmosis, I'll leave that for discussion by the chemists. So far popular opinions on the causes and cures of osmosis seem to fluctuate year on year - sometimes seeming contradictory. Sorry, not much help.

Rob.

 

[Seajet]

I was basing my input on the original, simply called 'gelshield' in the International data I just looked up; that was used as a precautionary treatment on top of gelcoat, not just peeled hulls.

I'd suggest a good look at the data and probably a chat with International would be the way to go; once any epoxy is on, it's ON !

 

[Jcorstorphine]

Gelshield Plus is solvent free but that is for building up after peeling isn't it? You'll be comparing with Gelshield 200 which is not solvent free.
If I were in your shoes I would use the stuff you've got - but I'm not a chemist.
If I wanted to buy marine high build epoxy primer - not solvent free - I'd get Jotun from Shepherd Marine a lot cheaper.

I think you have highlighted my situation exactly. The hull does not appear to have any blistering and the gelcoat is still in place albeit abraded by previous owner. As you say, I do not need to replace the gelcoat however I feel that I need to apply some form of barrier.

My thought would be to give the hull a wash with Acetone and allow it to dry then apply a thin (not thinned with thinners) almost transparent coating of my industrial Epoxy Paint using a well “squeegeed” out roller. This would be followed by a number of subsequent layers to establish some form of barrier (I know paint is not a barrier but then I am only trying to replace the top glossy gelcoat.

 

[Plevier]

I've never seen any recommendation to start with a thin coat when using epoxy. It seems normal to use a full coat but cure adequately before next coat.

 

[oldsaltoz]

I suspect that in your position I would go with what I have, epoxy based products stick very well, however there is no substitute for good preparation.

I would wash the area with Acetone to remove any contaminants then abrade the area wash with Acetone again, allow to dry and apply the product as directed my the maker (No thin coat first).

I do a lot of work with epoxies and the above procedure is quick and not too expensive but ensures a trouble free application.

Good luck and fair winds.

 

[johnlilley]

One of the advantages of solvent free epoxy is that you can wet on wet coat without fear of solvent encapsulation. If you wet on wet of solvent based then the solvent can become trapped because the coatings cure off before the solvent can escape.The trapped solvents can the cause later chemical interaction with the water that is very slowly in the case of epoxy, absorbed.
Use 1 coat at a time then that would probably be ok but you would have to abrade between coats to get good adhesion. For protection the overall thickness must be good & the adhesion must be good. Solvent based epoxies leave a slightly thinner coat but just apply more coats but let each one cure properly first.
That is my understanding of the differences of both.

John

 

[Elessar]

The whole point of gelshield is that it's solvent free.

In the early days of osmosis treatment / precautionary coatings, epoxy such as International 709 was used.

Then it was discovered that the solvents in these epoxies can actually promote osmosis !

So solvent free Gelshield and its' competitors were developed.

It sounds like your handy epoxy may not be a good idea...

Well it is, and it isn't.

The gelshield 200 everyone uses on hulls is solvented. only 45% solids in fact so 55% solvent. Dry film thickness less than 45 microns.

There is a solvent free gelshield plus for osmosis repairs, but it isn't what most people call gelshield.

 

[Elessar]

Gelshield Plus is solvent free but that is for building up after peeling isn't it? You'll be comparing with Gelshield 200 which is not solvent free.
If I were in your shoes I would use the stuff you've got - but I'm not a chemist.
If I wanted to buy marine high build epoxy primer - not solvent free - I'd get Jotun from Shepherd Marine a lot cheaper.
In fact here's information quoted from Malcolm at Shepherd (I've no connection just a customer):

Gelshield 200, which is the International equivalent of Jotun Penguard HB is only 45% volume solids as opposed to 54% for Penguard! Only Gelshield Plus, the gelcoat replacement, is solvent free.
The thing about solvent free primer being required for waterproofing/osmosis protection is a complete myth. There is a risk when using solvented products of getting solvent trapped in the paint, which subsequently become pinholes. This only happens if you apply successive coats before the previous coat is “through dry” (i.e. all the solvent has evaporated) or you continue to apply the paint when it is past its mixed “pot life”. Some people even try to extend the pot life by adding thinners, which is asking for trouble. The other thing people aren’t aware of is that if you use solvented products, you need more coats. In the case of Gelshield 200, the dry film thickness is only 45% of the wet film thickness, so you need more than twice as many coats to achieve a given dry film thickness than if you’re using solvent free products. This isn’t fully appreciated, so often there isn’t a high enough overall DFT applied of solvented products to give good protection.

all correct IMO

 

[Elessar]

One of the advantages of solvent free epoxy is that you can wet on wet coat without fear of solvent encapsulation. If you wet on wet of solvent based then the solvent can become trapped because the coatings cure off before the solvent can escape.The trapped solvents can the cause later chemical interaction with the water that is very slowly in the case of epoxy, absorbed.
Use 1 coat at a time then that would probably be ok but you would have to abrade between coats to get good adhesion. For protection the overall thickness must be good & the adhesion must be good. Solvent based epoxies leave a slightly thinner coat but just apply more coats but let each one cure properly first.
That is my understanding of the differences of both.

John

correct, but remember solvented generally has an infinite overcoating window, if solvent free is fully cured it needs to be abraded.

 

[savageseadog]

I used a solvent free industrial epoxy made by Ebalta for a hull protection coat. It was considerably cheaper at about 10 pounds per Kilo, plus I had some to hand. Three issues for me was long setting time, putting it on too thickly and getting runs and the lack of colour which made it difficult to see where it had been applied. The result was excellent.

 

[Seajet]

Well it is, and it isn't.

The gelshield 200 everyone uses on hulls is solvented. only 45% solids in fact so 55% solvent. Dry film thickness less than 45 microns.

There is a solvent free gelshield plus for osmosis repairs, but it isn't what most people call gelshield.

As I mentioned, I was referring to the relatively early days when there was just 'Gelshield', solvent free, which was used for peeled hulls and preventative treatment on gelcoats, inc mine.

Gelshield Plus & 200 are unfamiliar to me, though solvent free still seems worthwhile, I was under the impression that boats which had used stuff like 709 as a preventative coating on gelcoat sometimes ran into trouble ( I knew someone with a Konsort this happened to ) though of course determining the epoxy was at fault sounds rather tricky...

 

[vikinglish]

IMHO, this has overcomplicated things.

On a healthy hull the key is mechanical adhesion and proper drying times... Or more. Sound, clean mechanically abraded substrate, coat of decent 2 pack epoxy... Properly cure, abrade and apply second coat, repeat and third coat. Dont leave any risk of uncured epoxy or unabraded epoxy before applying the next coat. From personal experience Id put copper coat on the finished job and forget about osmosis risks. Hulls already suffering from osmosis need a different approach. Simple.... And I'm a chemist, though no longer in the profession

 

[Plevier]

all correct IMO

Elessar

It's recommended to give a couple of coats of epoxy primer before Coppercoat. Can I take it from this post that you aren't too fussed over which make? What is the solids content in the one Coppercoat offer please?