Lining fibreglass tanks

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seaangler23

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I have 2 large Inbuilt 450l diesel tanks in the boat and the original paint used to line these has failed and flaking off, plan is to clean, scrape, degrease and sand the walls (one of being the hull) then coat them with a suitable coating, the problem is most of the off the shelf coatings ive found are meant for car/bike tanks and would cost a small fortune to coat these tanks, I’ve found a polyester resin that’s meant for this but I feel it’s more meant for laying up a tank and a secondary bond with excisting glass isn’t ideal, I’d also like it to be coloured so inspection is easy and problem areas can be identified ( will only be doing one tank this year then opening it up to see how it’s faired before doing the other). The capacity of the tanks is well above what I need and I could use a bladder but either way I’d want it cleaned and painted, any ideas on a suitable coating?
 
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seaangler23 said:
I have 2 large Inbuilt 450l diesel tanks in the boat and the original paint used to line these has failed and flaking off, plan is to clean, scrape, degrease and sand the walls (one of being the hull) then coat them with a suitable coating, the problem is most of the off the shelf coatings ive found are meant for car/bike tanks and would cost a small fortune to coat these tanks, I’ve found a polyester resin that’s meant for this but I feel it’s more meant for laying up a tank and a secondary bond with excisting glass isn’t ideal, I’d also like it to be coloured so inspection is easy and problem areas can be identified ( will only be doing one tank this year then opening it up to see how it’s faired before doing the other). The capacity of the tanks is well above what I need and I could use a bladder but either way I’d want it cleaned and painted, any ideas on a suitable coating?
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I can't imagine a worse or more prone to failure job that recoating the inside of a GRP hull tank that has had diesel in it. Might work with a pretrol tank or with diesel if the tank could be removed, degreased several times, steam cleaned etc, but if part is the hull it looks like a recipe for failure. Bits of flaking off coatings would really not be good in a fuel line.....
 
I’d agree it likely would be a best not to coat but as it has and the paint is flaking and causing problems I can only scrape and sand it back, at which point it’s removed the barrier to the fibers and I’m unsure what damage can be done over time, with a good enough clean and decent sand surely so epoxy with a bit of pigment would be my best bet?
 
seaangler23 said:
I’d agree it likely would be a best not to coat but as it has and the paint is flaking and causing problems I can only scrape and sand it back, at which point it’s removed the barrier to the fibers and I’m unsure what damage can be done over time, with a good enough clean and decent sand surely so epoxy with a bit of pigment would be my best bet?
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If the GRP was properly laid up, the mat should have been well wetted with resin, which should seal the fibres. If the paint is flaking off, the GRP will already have been soaked in diesel, and I doubt you could clean it well enough to get a reliable adhesion with a coating.
 
she’s very well built, the glass looks good under the paint but unsure if I could remove all the flaking paint without sanding it back and if I don’t I’m back to potentially the same issue as the stuff that’s held degrades
 
seaangler23 said:
she’s very well built, the glass looks good under the paint but unsure if I could remove all the flaking paint without sanding it back and if I don’t I’m back to potentially the same issue as the stuff that’s held degrades
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... or use a paint remover chemical?
 
Caution there is an ethanol additive in modern diesel that attacks paint and polyester fibreglass ..making polyester fibreglass tanks unusable in the long run..its probably this component that is flaking your paint and any new paint you coat it with and ultimately will soften a polyester glass fibre tank. I would just fit a bladder if that is feasible.
 
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Freebee said:
Caution there is an ethanol additive in modern diesel that attacks paint and polyester fibreglass ..making polyester fibreglass tanks unusable in the long run..its probably this component that is flaking your paint and any new paint you coat it with and ultimately will soften your glass fibre tank.
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I'm guessing "ultimately" may mean many years.
 
Some years ago I accidentally put diesel into my water-tank, which made a most terrible mess, stripping the original paint. After cleaning I coated inside with a solvent-free epoxy paint, which was expensive but still going strong after 5 years, when the yacht was sold. Ordinary epoxy paint is not safe with drinking water.
 
lw395 said:
Would it be feasible to line the tanks with stainless steel?
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They are fairly structural now and the tops of the tanks are the starboard skippers bunk and Port lockers floor so I would be a disruptive job, think I’m going to scrape the loose stuff and give it a good clean then open it back up after the season and see how it looks
 
Fiberglass is not a suitable material for diesel fuel tanks

Diesel will find holes that water won't and diesel will "wick" through the laid up glass..

6 Differences Between Crosslinked Polyethylene and FRP ...
May 29, 2019 - 2. Chemical Wicking into the Tank's Walls. Because of the structure of fiberglass, harsh chemicals can wick into fiberglass tank walls over time, compromising the tank life. Eventually, the chemical resin barrier on the interior wall is compromised and the chemical makes its way into the structural area of the tank.

But having said the above I have seen people swear by vinylester diesel fuel tanks being OK. ( I suppose you'd have to lay up the vinylester on the outside of the tank)

NOTE
Re: Leaking fiberglass fuel tank
Odds are, based on years of oil business expereince, that the fuel has permeated the FRP just enough that nothing is going to bond. The probability of pealing is very high. Additionally, the tank may be leaking due to failure of the laminate; it's not some pinhole corrosion issue.
I'd build a new one, using a more suitable resin.
Leaking fiberglass fuel tank - SailNet Community
 
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I've been involved with coating and repairing used FRP tanks.

The reason for the coating is that the structural resin is owten not compatable with all fuel, particularly if some ethanol or biodiesel gets in there (any they get in there whether you buy those products or not, because of cross-contamination in the distribution business). Thus, a veil coat is often applied. It is the veil coat that is pealing. And losing the veil can be trouble. This was mostly done when ethanol and bioD were just new. It's not a good practice.

You have practically no chance of getting a good bond, since the diesel will have seeped int o the old coating. Not much, but it won't stick. Sanding won't help.

As for the notion that FRP is not suitable for diesel, that is obviously false. The majority of underground tanks are fiberglass because in many ways it is the best material (no corrosion). But they can be poorly made. The problem is the boat builder, not the material. Too often they build the structure from the same resin as the boat, instead of using a fuel-rated resin for the whole tank.
 
thinwater said:
I've been involved with coating and repairing used FRP tanks.

The reason for the coating is that the structural resin is owten not compatable with all fuel, particularly if some ethanol or biodiesel gets in there (any they get in there whether you buy those products or not, because of cross-contamination in the distribution business). Thus, a veil coat is often applied. It is the veil coat that is pealing. And losing the veil can be trouble. This was mostly done when ethanol and bioD were just new. It's not a good practice.

You have practically no chance of getting a good bond, since the diesel will have seeped int o the old coating. Not much, but it won't stick. Sanding won't help.

As for the notion that FRP is not suitable for diesel, that is obviously false. The majority of underground tanks are fiberglass because in many ways it is the best material (no corrosion). But they can be poorly made. The problem is the boat builder, not the material. Too often they build the structure from the same resin as the boat, instead of using a fuel-rated resin for the whole tank.
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" As for the notion that FRP is not suitable for diesel, that is obviously false"

Ethanol content can damage fiberglass fuel tanks | The Argonaut Newsweekly

 
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