Experience with epoxy barrier on wet hull?

[merjan]

Hi,

I'm wondering if anyone has real-life experience with putting an epoxy barrier on a wettish hull, and whether their boat started developing blisters faster than it would without an epoxy barrier. I am aware of the theoretical advice against an epoxy barrier unless your hull is drier than 5 on the Sovereign Scale A. I also (kind of) understand why that might be the case. What I am wondering is how common this is in practice and whether anyone has suffered prophesied consequences. I'd be very interested to hear real-life experiences.

Some background in case you're wondering why I might be contemplating doing that:
Our boat is in our ownership since May 2022, and she has a 40+ year old GRP hull. The claim is that in 2019 the hull was sanded back to GRP, faired and International VC Tar (Epoxy) was applied on it. I sanded off all 5 coat of paint on it, including an innermost black layer which I presume is the claimed VC Tar epoxy. (I'm not sure if it was doing anything if it was thin enough to be sanded off relatively easily with P40 mesh discs.) I am now left with with a blueish grey paint on the GRP which is most difficult to remove. I am guessing this is a fairing compound or another primer, but I am unable to identify the product. I'm not attacking this layer until I know how to coat the hull next. I should also add that after 3 months ashore, a vintage analogue Sovereign meter reads between 15 - 18 on scale A.

I am tempted to apply a coat of Jotun Penguard, mainly because the boat is claimed to have had an epoxy primer for three years and doesn't have any blisters. And if the boat does get blisters, surely blisters that are dealt with are better than more water getting into the hull?

Any advice / comments would be most appreciated!

Ömer

 

[Tranona]

Blisters are not caused by "water getting into the hull", but fluid, usually styrene from uncured resin getting through the gel coat. If the hull does not have blisters by now it is unlikely to develop any in the future. Suggest just prime it with Vinyguard and antifoul.

 

[penfold]

What he said; prime, antifoul and go sailing. If it blisters, deal with them then. A lot of expensive paint is sold on the back of not much science.

 

[Stemar]

A damp layup is only a problem if there are big voids in it, which will have made themselves known by big blisters. If that's the case, you won't solve it with a dew coats of epoxy, but it will be obvious.

Smaller blisters - an inch or two across - can be dealt with by grinding out and filling when convenient and not worrying about them when it isn't convenient.

 

[geem]

Hi,

I'm wondering if anyone has real-life experience with putting an epoxy barrier on a wettish hull, and whether their boat started developing blisters faster than it would without an epoxy barrier. I am aware of the theoretical advice against an epoxy barrier unless your hull is drier than 5 on the Sovereign Scale A. I also (kind of) understand why that might be the case. What I am wondering is how common this is in practice and whether anyone has suffered prophesied consequences. I'd be very interested to hear real-life experiences.

Some background in case you're wondering why I might be contemplating doing that:
Our boat is in our ownership since May 2022, and she has a 40+ year old GRP hull. The claim is that in 2019 the hull was sanded back to GRP, faired and International VC Tar (Epoxy) was applied on it. I sanded off all 5 coat of paint on it, including an innermost black layer which I presume is the claimed VC Tar epoxy. (I'm not sure if it was doing anything if it was thin enough to be sanded off relatively easily with P40 mesh discs.) I am now left with with a blueish grey paint on the GRP which is most difficult to remove. I am guessing this is a fairing compound or another primer, but I am unable to identify the product. I'm not attacking this layer until I know how to coat the hull next. I should also add that after 3 months ashore, a vintage analogue Sovereign meter reads between 15 - 18 on scale A.

I am tempted to apply a coat of Jotun Penguard, mainly because the boat is claimed to have had an epoxy primer for three years and doesn't have any blisters. And if the boat does get blisters, surely blisters that are dealt with are better than more water getting into the hull?

Any advice / comments would be most appreciated!

Ömer

Are you sure the boat has not had epoxy treatment in the past? The blueish grey could be epoxy? You may be removing something you really don't want to be removing

 

[merjan]

Thank you all for the responses! It sounds like I shouldn't feel bad about having removed the VC Tar.

Are you sure the boat has not had epoxy treatment in the past? The blueish grey could be epoxy? You may be removing something you really don't want to be removing

That's why I left it in tact as much as I can. I might have thinned it in places.I've certainly exposed fibreglas in some spots but not many. However given the relatively high moisture readings, that blueish grey can't be doing much as a berrier? If it did, I should be reinforcing it with more epoxy, and the advice is against that.

 

[dankilb]

There must’ve been a reason why a previous owner added the 5 coats of barrier. Now you’ve removed it, I can see you’ve got a bit of a dilemma!

A hull with glass showing in places is, IMHO, not a good candidate for ‘antifoul and go sailing’.

Assuming you’re in the UK, you’re also now not at a good time of year to redo any barrier coat (the TDS might say it’ll cure in cold conditions - but that is for the professionals using the paint as prescribed to coat steel, not GRP in a cold, damp boatyard).

 

[geem]

Thank you all for the responses! It sounds like I shouldn't feel bad about having removed the VC Tar.



That's why I left it in tact as much as I can. I might have thinned it in places.I've certainly exposed fibreglas in some spots but not many. However given the relatively high moisture readings, that blueish grey can't be doing much as a berrier? If it did, I should be reinforcing it with more epoxy, and the advice is against that.

If the hull is very wet then you could have the epi

Thank you all for the responses! It sounds like I shouldn't feel bad about having removed the VC Tar.



That's why I left it in tact as much as I can. I might have thinned it in places.I've certainly exposed fibreglas in some spots but not many. However given the relatively high moisture readings, that blueish grey can't be doing much as a berrier? If it did, I should be reinforcing it with more epoxy, and the advice is against that.

Why did you remove the VC Tar? The boat will likely have high readings if you have just removed it from the water. After a winter on the hard the moisture readings would likely be lower. I am not sure what you are trying to achieve or why you have removed an epoxy barrier coat. If you don't have blisters then why are you doing anything?

 

[merjan]

I don't think the five coats were all barrier. In fact I'm attaching an unsolicited bottom pic. The layers go as pale green -> red -> black -> white -> black until the blueish grey unidentifiable coating on the GRP. That's not the current status of the bottom, but an intermadiate stage that shows all of the coats that were on.

The claim is that the barrier coat was VC Tar, which is black so it must be the stuff on the blueish grey. It came off relatively easily (and wasn't doing much given the moisture readings). I interpret "antifoul and go" as three coats of Vinyguard + two coats of AF.

Apparently with the cold weather additive Jotun Penguard HB cures in 2ºC on GRP, but I'll hold fire until March when we hope to relaunch, and keep an eye on the moisture levels.

There must’ve been a reason why a previous owner added the 5 coats of barrier. Now you’ve removed it, I can see you’ve got a bit of a dilemma!

A hull with glass showing in places is, IMHO, not a good candidate for ‘antifoul and go sailing’.

Assuming you’re in the UK, you’re also now not at a good time of year to redo any barrier coat (the TDS might say it’ll cure in cold conditions - but that is for the professionals using the paint as prescribed to coat steel, not GRP in a cold, damp boatyard).

 

[merjan]

If the hull is very wet then you could have the epi

Why did you remove the VC Tar? The boat will likely have high readings if you have just removed it from the water. After a winter on the hard the moisture readings would likely be lower. I am not sure what you are trying to achieve or why you have removed an epoxy barrier coat. If you don't have blisters then why are you doing anything?

My goal was to remove all antifouling and start afresh by topping up the primer. I had forgotten about the VC Tar but to be honest I imagine I would have noticed it if I hit a coat of epoxy coat in the process. (Surely that doesn't come off like antifouling.). The keel has Jotamastic on and it certainly is a lot tougher than the suspected coat of VC Tar.

The boat's been ashore since the beginning of September. The bilges are dry. If the readings do drop in time as you say, then it'll be a good time to apply a more robust epoxy coat. If they don't drop, then the barrier wasn't doing its job anyway.

 

[geem]

When you took the moisture readings was the hull dry. No condensation, no rain. Epoxy is a far better moisture barrier than polyester gelcoat. Its hard to understand how it couldn't be doing its job. If there were no blisters then removing the antifouling and applying new was all that was necessary. By exposing parts of the glass laminate you have created the need to now apply an epoxy barrier system to those parts and fill and fair so as not to create any nasty uneven surface. In my mind, a lot of unnecessary work for no gain.

 

[RunAgroundHard]

My goal was to remove all antifouling and start afresh by topping up the primer. I had forgotten about the VC Tar but to be honest I imagine I would have noticed it if I hit a coat of epoxy coat in the process. (Surely that doesn't come off like antifouling.). The keel has Jotamastic on and it certainly is a lot tougher than the suspected coat of VC Tar.

The boat's been ashore since the beginning of September. The bilges are dry. If the readings do drop in time as you say, then it'll be a good time to apply a more robust epoxy coat. If they don't drop, then the barrier wasn't doing its job anyway.

Moisture gets trapped anyway after it reacts with uncured chemicals and the levels may never drop, unless the hull is subject to something like a HotVac process, post exposure of GRP. You have wasted your time and likely set up conditions for wicking on the exposed glass mat. You need to sort out any exposed glass mat first. Don't be surprised if the moisture levels do not drop.

Owner of a 40+ year old boat, same process VCTar et cetera. I would never have dreamed doing what you have done. I anti foul with eroding anti foul every two years on top of old anti foul, after scraping off any loose stuff. I have a Tramex Skipper Plus meter and over the years, against bare hull, I have not seen much change, even after all winter ashore. I will probably have the hull soda / dry ice blasted next year, maybe scrape back if the pennies are low. My advice is don't get hung about this anymore, get the hull prepped and anti fouled, you have an old hull, live with whatever moisture readings exist and forget about osmosis as a threat. If you do see blister's treat them, as other have said, no more than that.

 

[merjan]

When you took the moisture readings was the hull dry. No condensation, no rain. Epoxy is a far better moisture barrier than polyester gelcoat. Its hard to understand how it couldn't be doing its job. If there were no blisters then removing the antifouling and applying new was all that was necessary. By exposing parts of the glass laminate you have created the need to now apply an epoxy barrier system to those parts and fill and fair so as not to create any nasty uneven surface. In my mind, a lot of unnecessary work for no gain.

Perhaps - but at least I will know what's on my boat, which matters to me! I am continously taking readings during various weather conditions, before and after running a dehumidifier. It doesn't seem to affect the readings. It may be that the epoxy is applied on a wet hull, which at least partly justifies the removal.

 

[geem]

Perhaps - but at least I will know what's on my boat, which matters to me! I am continously taking readings during various weather conditions, before and after running a dehumidifier. It doesn't seem to affect the readings. It may be that the epoxy is applied on a wet hull, which at least partly justifies the removal.

But you had no blister therefore you had no problems ragardless of how wet the hull might be. A wet hull wont sink the boat. Taking readings of the hull through a moisture resistant epoxy barrier isn't going to tell you the moisture content of the laminate which is why I asked about condensation on the hull

 

[merjan]

Moisture gets trapped anyway after it reacts with uncured chemicals and the levels may never drop, unless the hull is subject to something like a HotVac process, post exposure of GRP. You have wasted your time and likely set up conditions for wicking on the exposed glass mat. You need to sort out any exposed glass mat first. Don't be surprised if the moisture levels do not drop.

Owner of a 40+ year old boat, same process VCTar et cetera. I would never have dreamed doing what you have done. I anti foul with eroding anti foul every two years on top of old anti foul, after scraping off any loose stuff. I have a Trammel Skipper Plus meter and over the years, against bare hull, I have not seen much change, even after all winter ashore. I will probably have the hull soda / dry ice blasted next year, maybe scrape back if the pennies are low. My advice is don't get hung about this anymore, get the hull prepped and anti fouled, you have an old hull, live with whatever moisture readings exist and forget about osmosis as a threat. If you do see blister's treat them, as other have said, no more than that.

I see - if the readings are not falling like in your case, then I'll fair over the exposed fibreglass, prime generously, antifoul, and hope for the best. By the way, by "exposed glass" I mean visible glass like in the photo. I hope it's not too bad! Would Intenational Watertite be good to cover these patches with?

 

[merjan]

But you had no blister therefore you had no problems ragardless of how wet the hull might be. A wet hull wont sink the boat. Taking readings of the hull through a moisture resistant epoxy barrier isn't going to tell you the moisture content of the laminate which is why I asked about condensation on the hull

I took readings also on very dry days (even seldom, we did have a couple) with the hull externally dry - no condensation. I also took readings through the gaps where I can see glass fibres. No difference.

 

[RunAgroundHard]

I see - if the readings are not falling like in your case, then I'll fair over the exposed fibreglass, prime generously, antifoul, and hope for the best. By the way, by "exposed glass" I mean visible glass like in the photo. I hope it's not too bad! Would Intenational Watertite be good to cover these patches with?

I think what you are seeing is clear resin / gell coat below the water line, which can show the glass strands*. Many yacht builders only used coloured gell coat above the water line. The glass strands, if fully wetted should not be visible, so you have some dry strands showing in the resin. There is not much you can do about it. This advice is amateur based, old boat owner, so happy to be corrected. Dry strands can cause wicking of moisture if exposed to the outside environment.

I have similar areas below water line where I removed anti fouling and cleaned up to expose surface GRP. The photos show glass strands like yours but not so dense, fewer clear glass strands in my case. However, these may be just at the surface and the rest of the layup is fully wetted out and you have good hull strength. Again, don't worry about it. Why? Because the boat is old and the hull has been sailing about without catastrophically failing - like many, many old hulls, that is the statsiscal evidence in your favour. It is also wrong to extrapolate a surface visual examination as indication of the whole hull and condition deep in the lay up.

It is worth buying "Surveying Yachts and Small Craft" by Paul Stevens. In the first edition, he shows pictures showing exactly what you see. Note that the more you read, the more you can be convinced that the boat is about to catastrophically fail, as terms such as "serious", "expensive", "progressive" are used. Remember, the statistics don't show that, and many, many owners of old boats have not went down the road of so called osmosis treatments and have been sailing around confidently.

*What you see are not single strands but bundles of tiny strands that look like a single strand - you need a microscope to see the individual strands.

 

[Tranona]

I see - if the readings are not falling like in your case, then I'll fair over the exposed fibreglass, prime generously, antifoul, and hope for the best. By the way, by "exposed glass" I mean visible glass like in the photo. I hope it's not too bad! Would Intenational Watertite be good to cover these patches with?

I have a 1979 boat which I bought just over a year ago. Low moisture readings, indeed almost the same as on your boat, and with similar patches where the epoxy barrier had broken away. Advice from the surveyor was not to disturb anything - the antifoul was eroding type and very fair, but to fill and fair with Watertite in the patches then prime and antifoul. I used CuPro primer and AF smlmarinepaints.co.uk/antifouling/CU-PRO. Time will tell but pretty confident.

 

[merjan]

Thank you to everyone who responded. I received some very helpful comments. It is interesting that some of the advice seem to be conflicting: "epoxy barrier on wet hull is a bad idea" vs "removing the epoxy barrier from a wet hull is a bad idea". I agree it's best not to distrub something that works, but what happened has happened, and at least we'll know what's on our boat. I'll monitor the moisutre levels, and make a call in March.

 

[dankilb]

Thank you to everyone who responded. I received some very helpful comments. It is interesting that some of the advice seem to be conflicting: "epoxy barrier on wet hull is a bad idea" vs "removing the epoxy barrier from a wet hull is a bad idea". I agree it's best not to distrub something that works, but what happened has happened, and at least we'll know what's on our boat. I'll monitor the moisutre levels, and make a call in March.

Applying a barrier to a wet hull is a bad idea. The concerns mainly surround poor adhesion and/or subsequent blistering. Removing a barrier (or really doing anything other than treat blisters) on a wet hull is highly 'debatable' - if mainly for the point others have made, that 'osmosis' is a factor of many hyrdoscopic substances/processes that build up over years/decades. The hull is unlikely to dry with the coating removed (beyond the very first few days/a week post lift-out) - just as much as it was unlikely to suffer/react with the coating left on (it sounds as if blisters hadn't shown in the years since it was applied).

I can speak from some experience re: applying these things in marginal conditions, because we completed a pretty extensive barrier coating job in N Wales last September thru November. The rationale for this was extensive previous osmosis (minor blisters - but lots of them); the hull had passively dried over 6 years on the hard (under previous ownership); blasting revealed the gel coat was paper thin in places and opened up many of the blisters; and our make/model has both a reputation for minor blistering and also one for responding favourably to epoxy coating as a treatment. (I have opinions about why this is - re: quality of the resin/mix used - but that's not for this thread)

We had the boat professionally blasted and after that we filled all the (likely thousands) of blisters and did an initial rough fairing, followed by 2 hot coats of pure laminating resin (this was tricky and I wouldn't necessarily suggest replicating); 4-odd coats of Penguard - then further/final fairing - and 3 coats of Jotamastic 87.

I can attest that Jotun products are fantastic, in terms of ease of application and value for money (time will tell on 'in service...'). But as I mentioned before, don't be thinking you can epoxy coat a hull in 2 degrees C or similar. There are other environmental factors (associated with UK winter weather) that will affect curing and may also reduce adhesion. We experienced this and did have some problems, but luckily only when we came to coat the patches under the props towards the (colder) end of the job. Cold GRP in a boatyard behaves qualitatively differently to cold steel in a shipyard/civil engineering site. Remember, the TDS minima are there to allow the pros to continue working on bridges/ships/oil rigs in the most marginal conditions. I would therefore agree that March is the very earliest to start thinking about this.

I'm obviously a convert to epoxy coating, otherwise I wouldn't have done it myself. Jotun is a joy to use, the prep on your hull is now mainly done (for better or worse!), the 'wet hull' didn't blister before, and so - on balance - I would probably cast my vote to recoat your hull with Penguard (5 coats minimum). I can see the appeal of 'go sailing' instead, too, of course!