Magnet in shower: How to protect against rust

Question

I've found a small lifehack involving shampoo using a magnet (strong magnet, not neodymium) to solve my "tipping the shampoo off the shampoo holder" and "nudging the shampoo holder off the wall" problems. Not that pretty but it does the trick. I tried to use a hook instead of magnets, but it was miserable at its job.

Magnet coating is prone to rust, so I've put it in a plastic zipper bag, rolled it up and bound it with adhesive. Rust will cause the magnet to brittle and possibly crackle and I don't want this to happen (I don't care if the binder clip rusts).

Despite those efforts I've started to notice traces of rust on the magnet. Water has effectively managed to enter the zipper bag; I blame capillary action.

I was wondering is there is a simple way to protect the magnet. I thought about epoxy glue or hot glue, but I have neither of those and also I'm not sure they are water resistant.

Answer 1

Waterproofing (rust-proofing) magnets is a common application in aquarium environments where you want to attach various fixtures to a glass/acrylic fish tank with a pair of magnets. You can actually purchase coated magnets that are meant for wet environments, but I'll stick to common DIY techniques that can make a magnet waterproof at home.

Waterproof Epoxy Putty

Water weld epoxy putty (for plumbing or repairing tubs, drains, fuel tanks, etc) is the easiest to work with. You can form the epoxy putty around the magnet in any shape you wish, then sand it down even further after it is dry. Bonus that epoxy putty has many other uses, and is generally useful to have around for a variety of other fix-it-yourself projects.

Product Search: Water Weld Epoxy Putty

Two-part Epoxy

Regular waterproof, two-part epoxy will work too. You can slobber it on and let it cure really well. The nice thing about epoxy in general is it is sandable and won't crack/chip with continued use.

Product Search: Waterproof epoxy

Multipurpose Rubber Dip

This is an air-dry multipurpose rubber coating which provides protection against water and can be sprayed on, painted on, or dipped directly into the product.

Product Search: Rubber Dip

Answer 2

Paint the magnet with a good enamel paint. Ensure that the whole magnet is completely covered. You may need to apply multiple coats of paint. Follow the manufacturer's instructions on how to apply the paint.

Depending on how the magnet is coated already, you may need to apply a coat (or more) of primer so that the enamel paint will adhere properly for a long term.

Answer 3

Try magnets modified for your specific requirement. There are two immediate possibilities.

- Rubberised neodymium magnets

Rubberised magnets are completely coated by a plastic layer. That makes them perfectly suitable for longterm use outdoors, in wet surroundings or even under water (e.g. in aquariums).
Their finish doesn't scratch surfaces as a normal magnet.
At the same time, they are much stronger than ferrite magnets of the same size.

- Ferrite magnets

Ferrite magnets are insensitive to humidity and can be used outdoors without rusting. A special protection is not necessary.
Pot magnets with ferrite magnets are also suitable for outdoor use. Surface rust may develop on the pots over time, but that does not impact the performance of the magnets. The magnets themselves are rust-proof.
Ferrite magnets are also resistant to most chemicals. However, solvents and certain concentrated acids may harm the magnets.

Either of these off-the-shelf "solutions," are cheaper than most of the materials you would need to encase magnets to hack them for your application. There may be others with a similar humidity extreme requirement.

Answer 4

Hot melt adhesive is pretty waterproof and if you have it available I would carefully paint the magnet with the hot melt. You can re-flow the glue with a hair dryer or gas lighter to smooth the surface if you are very careful not to get stuck to the molten glue.

A quick fix might be to put petroleum Jelly/Vaseline/Silicone grease into the bag with the magnet. These will repel water and keep the magnet dry.

Heat sealing the bag with a cheap dollar store food bag sealer should help, sort of like the expensive bag sealer from Staples.

Nice method would be to purchase a length of suitable diameter heat shrink tubing, preferably with the inside hot melt adhesive. If the tubing has the adhesive you can shrink it and press the ends shut when everything is soft and sticky, use books or wood blocks so they don't melt or burn you. If your heat shrink does not have the adhesive lining you can use your glue gun to place a generous bead of hot melt glue at each end of the magnet, when cold slip the shrink tubing over the magnet and re-heat with the hair dryer/hot air gun and proceed as above. If you leave a tail on the tubing you can use it as an attachment point.

A small plastic pill container may serve the same purpose.

An alternative is to use painted (or plastic coated) coathanger wire and wrap a bunch of turns around your bottle and not care if it rusts, just replace it with the new bottle and attach the magnet in a protected place so it does not remain wet.

EDIT:
One idea that might work is to drop some small chromed steel ball bearings into the shampoo bottle. Then pull them to a convenient place with a external (waterproof) magnet. You then just need to have a suitable iron spot to park your bottle. When the shampoo runs out you can recover or throwaway your ball bearings.