How to Make a Concrete Pen Holder for Your Desk

A concrete pen holder is a small, heavy desk organizer that keeps your favorite pen standing upright and always where you left it. It costs a few dollars to make. Sam Bucciferro of Fizzy Brick shows the whole process, including the first mold that failed and the changes that fixed it. You build a little foam board box, stand a pen in it, fill it with concrete and peel the mold away a day later.

How to make a concrete desk organizer: the short version

• Cut a base and four walls from foam board using a template.
• Cover the pieces in packing tape and hot glue them into a box.
• Push a taped, greased pen through a hole in the base.
• Sift the gravel out of the concrete mix, add water and fill the mold.
• Let it cure, pull the pen and peel off the foam board.

Why foam board makes a good mold

Pros cast countertops in melamine, but that is overkill for a cube this size. Foam board is cheap, cuts with a craft knife and glues in seconds. Its weak spot is the paper skin. Paper soaks up water, and concrete needs that water to cure hard. Sam's untaped mold lost so much moisture that the glue let go and the walls drifted apart. A layer of clear packing tape fixed it and gave a glossier, smoother face.

Getting the pen hole right

The pen itself makes the hole, so it fits your pen exactly. That is also the risk. On the first try the pen set solid in the concrete and never came back out. Wrap the end of the pen in a few turns of packing tape and wipe on a thin coat of petroleum jelly. The tape makes the hole a touch bigger, and the jelly lets the pen slide free. Use a cheap pen for casting, then swap in a nicer one.

Which concrete to buy

The cheapest bag of basic concrete mix at the hardware store works. Most of those mixes contain gravel, which is great for a patio and bad for a two-inch cube. Stones jam between the pen and the mold wall. Rub the dry mix over a screen or a sheet of cardboard punched with holes and keep only what falls through. A sand mix or countertop mix skips this step and gives a smoother finish.

Safety with dry concrete

Concrete dust is caustic. Wear gloves and a dust mask when you sift and mix, and work outside or near an open door. Rinse wet concrete off skin right away. Never wash leftover concrete down a sink drain.

Ideas to make it your own

• Glue a square of cork to the bottom so it will not scratch your desk.
• Make the mold taller or wider and cast holes for two or three pens.
• Tint the mix with a little pigment before you pour.
• Seal the cube so ink and coffee rings wipe off.

Common problems

• Pen stuck for good. Not enough tape or jelly. Add both next time.
• Walls separated. The paper soaked up water. Tape every inside face.
• Wobbly mold. Use a flat base and rest the mold on a can or cup while it cures.
• Pitted faces. Tap the mold after filling to release trapped air.

More concrete crafts

For more mold ideas, see concrete molds from household items. Learn how to fix air bubbles in concrete crafts and how to seal concrete crafts, then make a matching concrete catchall tray for the rest of your desk.