A customer in Norway for whom I built a North Star kayak, recently told me he was having corrosion issues with some of the rare earth magnets I used in his hatch covers and deck.

I knew this was a potential problem with the standard nickel plated rare earth magnets sold, so I was pleased to see special "black" epoxy coated DC2E rare earth magnets offered by K&J Magnets, stating this epoxy coating provided "extreme corrosion resistance", and "protects the magnet from rusting in wet conditions, including exposure to seawater",

These are the magnets I've been using for the last 8 to 10 years. I have not experienced any corrosion problems nor have I heard from any other customers who I've built boats for.

When I started using the nickel plated magnets in 1998 I found any contact with water caused them to expand and burst in a short period of time. So I made sure to encapsulate them under epoxy and fiberglass. Still, water can find ways, so I moved to the DC2E magnets as soon as I was aware of them.

So, are the claims for saltwater proof rare earth magnets true?

I asked Michael Paul the owner of K&J Magnets.

On 5/4/2016 4:08 PM, robm wrote:

Message:
I use your DC2E magnets to hold hatch covers on the sea kayaks I build professionally.
I have a customer in Norway who is having those magnets fail, by corrosion.
How are you determining the "extreme corrosion resistance", and "protect the magnet from rusting in wet conditions, including exposure to seawater", you claim
I need to be able to rely on your product claims.
What do I tell my customer?

K&J Magnetics
11:50 AM (1 hour ago)

to robm
Rob,

Please allow me to offer our sincerest apologies and an explanation of what's going on. Subjected to a wet, salt water environment, I would expect an epoxy coated neodymium magnet to corrode over time. If you're going to use DC2E magnets in such an environment, you'll want to somehow seal them from moisture.

The typical nickel-copper-nickel plating on most neodymium magnets provides good corrosion protection. Without it, the iron-based magnet quickly corrodes in just about any moisture. With the plating, it's a great solution for everything from hard drives to earphones. Still, the plating isn't what we'd call waterproof. Used underwater or outdoors for extended periods, they will begin to rust.

We offer a few magnets with black epoxy coating. According to some testing referenced on our Specs page, they can perform a bit better in some conditions. They're still not what we'd call rust-proof; they'll just last a bit longer.

For something that's long-term waterproof, you really need to seal the magnet off from moisture. This might involve painting it, potting it in place, or otherwise enclosing it. Our Plastic Coated Magnets are a popular off-the-shelf solution.

So why did that product page make those claims? It looks like that was a mistake. I believe it's because that description was written a long time ago, when we first started offering epoxy coated magnets. While epoxy coaters claim it's that good, our own subsequent experience showed that they could rust over a long enough time. We somehow missed updating that particular product page.

We've updated the DC2E product page to match our other epoxy coated magnets like the D82E.

We're very sorry for the mistake, and the position it puts you in with your own products. Please let us know if there's anything we can do to help solve the problem or find a new solution.

Best Regards,

Michael Paul
K&J Magnetics, Inc.
www.kjmagnetics.com

I'm publishing this on this BB because I know a lot of you like my magnetic hatch cover system and I want to give you a heads up on the potential for corrosion issues.

I think using these magnets is still a good option, however I personally will be more vigilant in encapsulating the magnets in epoxy with a layer of lightweight glass over top to ensure as waterproof an environment as possible. Special attention must be paid to any adjacent un-glassed wood coated only with epoxy as possible moisture entry points. Attention must be paid to repairing normal wear.

Finally, rinsing salt water off with fresh water after use and storing with hatch covers open will likely extend the life of magnetic hatches.

All the best,
Rob