Polyurethane vs Epoxy: Choosing the Right Coating for Water Tank ...

When it comes to relining water tanks, selecting the appropriate coating is crucial for ensuring longevity, safety, and compliance. Two commonly used materials are polyurethane and epoxy coatings. Each has distinct properties that make them suitable for different applications. This article aims to provide facilities managers with a comprehensive comparison to aid in informed decision-making.

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Understanding Polyurethane and Epoxy Coatings

Polyurethane Coatings

Polyurethane coatings are known for their flexibility and resistance to UV radiation. They are often used in environments where temperature fluctuations occur, as they can accommodate substrate movement without cracking. Additionally, polyurethane coatings cure relatively quickly, reducing downtime during application.

Epoxy Coatings

Epoxy coatings are renowned for their hardness and strong adhesion to various substrates. They provide excellent chemical resistance, making them suitable for environments where the tank contents may be aggressive or corrosive. However, epoxies are generally more rigid and may not perform as well under conditions involving structural movement.

Key Considerations for Water Tank Relining

Durability and Flexibility

• Polyurethane: Offers superior flexibility, making it ideal for tanks that experience temperature-induced expansion and contraction.

• Epoxy: Provides a hard, durable surface but may be prone to cracking if the substrate moves.

Chemical and UV Resistance

• Polyurethane: Exhibits good resistance to UV radiation, maintaining its integrity and appearance over time.

• Epoxy: While chemically resistant, epoxies can degrade under prolonged UV exposure, potentially leading to discoloration and reduced performance.

Application and Curing Time

• Polyurethane: Typically cures faster than epoxy, allowing for quicker return to service.

• Epoxy: Generally requires a longer curing period, which may extend downtime during maintenance.

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Suitability Based on Tank Material and Use

Concrete Tanks

• Polyurethane: Its flexibility makes it well-suited for concrete tanks, accommodating any minor movements or settling.

• Epoxy: Can be used on concrete but may require additional surface preparation to ensure proper adhesion.

Steel Tanks

• Polyurethane: Provides a protective barrier against corrosion, especially in outdoor settings where UV exposure is a concern.

• Epoxy: Offers excellent adhesion to steel surfaces and strong chemical resistance, beneficial for tanks storing aggressive substances.

Potable Water Storage

Both polyurethane and epoxy coatings can be formulated to meet safety standards for potable water. It's essential to verify that the chosen product complies with relevant regulations and certifications. For instance, in the UK, the chose produce should be WRAS or KIWA approved.

Maintenance and Longevity

• Polyurethane: Its flexibility can lead to a longer service life in environments with structural movement or thermal cycling.

• Epoxy: Offers a hard, durable finish that resists abrasion but may require more frequent inspections in dynamic environments.

Conclusion

Selecting between polyurethane and epoxy coatings for water tank relining depends on various factors, including tank material, environmental conditions, and the nature of the stored contents. Polyurethane's flexibility and UV resistance make it suitable for outdoor and concrete tanks, while epoxy's hardness and chemical resistance are advantageous for steel tanks and aggressive substances.

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Anybody have any thoughts on epoxy coating the inside of steel diesel tanks? I don't have any experience with it, but am in need of options for mine, an aging set on a GB36. Also, do you know of places in Puget Sound that do it?

To coat the tanks properly they need to be removed from the boat. If you're going to remove the tanks, why not replace them with tanks with sumps, built out of Al and then epoxy coated.

If the rust is only on the top as a result of the fill spout or bad decks, you can coat the tops with a product such as POR-15. It's not a complete fix but may be good enough with out having to replace the tanks, assuming they aren't rusted thru.

I would be concerned that it would chip or flake off at some point and clog up the system.
For those who have done this, is it a real concern?

We did the same thing Kieth did in the post referenced previously. I did the work myself and there have been no issues. Our insides were sludge and I was concerned about pitting/crevice corrosion along the bottom, the lowest corner and the associated seams. I did it as PM only, since we had no leaks. After cleaning the forward chamber, multiple wipe downs with acetone, I applied Flamemaster . A bit of a PIA since the whole operation is done through a 9" inspection port.

http://flamemaster.com/wp-content/uploads//07/CS-rev-01-07.pdf

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We did the same thing Kieth did in the post referenced previously. I did the work myself and there have been no issues. Our insides were sludge and I was concerned about pitting/crevice corrosion along the bottom, the lowest corner and the associated seams. I did it as PM only, since we had no leaks. After cleaning the forward chamber, multiple wipe downs with acetone, I applied Flamemaster . A bit of a PIA since the whole operation is done through a 9" inspection port.

http://flamemaster.com/wp-content/uploads//07/CS-rev-01-07.pdf

Larry, beautiful work. I'm thinking of doing the same thing as PM. Do your tanks not have baffles? Or is there access through the baffles?

Larry, beautiful work. I'm thinking of doing the same thing as PM. Do your tanks not have baffles? Or is there access through the baffles?

2-350 gallon tanks with 3 baffles per tank. I was able to see with an endoscope and also a flashlight/mirror into the other chambers. They slope significantly up from the low end where the inspection port is. After the fuel was pumped out they looked good. All the sludge had pretty much collected in the low end. After talking to other Krogen owners, the weak link on the 42's tanks, seems to be at the low end and leaks from the inside out. I suppose it's possible to butch-up a repair of a leaking fuel tank by slobbering the interior with some kind of goo, or an epoxy of some sort on the exterior, or other band aide measures. They may well work for the remaining time that particular owner owns the boat. Or not-your mileage may vary.

Enthusiastic references have been made on this forum to tank coatings used in the aviation industry. No mention of the FAA-mandated routine inspection of such coated tanks, FAA-mandated removal and replacements of such coatings to retain aircraft certifications, no mention of the cost associated with the apparent success of such coatings in aviation use, etc.

I've also read on this forum an advocate of opening his tanks, crawling inside, and having a welder repair leak points from the inside. Seriously? I made a similar inquiry, for the same reasons, a couple of years ago in the Everett, WA area. I was met with absolute refusal by EVERY welder I could find to weld inside a tank previously filled with ANY hydrocarbon (ie-diesel), inside a flammable boat. Can you spell explosion, asphyxiation, or fire?They thought I was crazy, and no one would risk it. I'd love to meet that guy's welder. I expect he is a few bricks short of a full load.

Should you be fortunate enough to access all areas of either actual or suspected leaks, via inspection ports or man-sized access ports, then gooping them up may well work for you. It may well work for many years. But do the next owner a favor and disclose this fix to the potential next owner and his surveyor prior to sale. I'm betting they run for the hills. I certainly would.

All rants above are my personal opinion, of course. They are, however, backed with solid, direct experience in diagnosing and repairing leaks in water and fuel tanks aboard pleasure boats, and other professional experience in related subjects. So, for what it's worth, my conclusions for all leaking fuel AND water tanks aboard pleasure boats is remove and replace. Sounds harsh ($$), and it is. My safety and piece of mind is worth the money, and my conscience is clear when I pass on my boats to others.

Regards,

Pete Agree with jungpeter on this one. I went thru the same dilemma with our 71 Grand Banks 36 and came to the conclusion that cutting the old tanks out and starting over was the best route to go. It's a dirty, stinky nasty job but once the old tanks were out, I was able to scrub the area underneath and give it a fresh coat of bilge paint. New tanks were made from 3/16 Aluminum with measurement to allow bringing them in thru the aft cabin. We lost a bit of capacity but it's a small trade-off for the piece of mind of all new tanks and no more diesel smell. Total cost was under $2,000 for the new tanks and I did all the rest of the work myself. Good luck with your project.
Stan