Meg's magnet board does double duty. It's made from sheet metal that was painted with chalkboard spray paint. You can learn all about it here. You should be able to find sheet metal at your local hardware store and at Home Depot. Check the scraps and plumbing section, and bring a magnet to make sure you're buying the right one. You can mount a metal sheet directly to the wall, onto a piece of wood or slide it into a frame. To add a coastal theme, magnetize shells, beach rocks, driftwood or pretty seaglass pieces as shown below!
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