This is a fairly easy to make decorative concrete lamp, via hacking an IKEA light fitting.

Supplies

IKEA SEKOND ceiling lamp set [UK IKEA]
IKEA ROLLSBO light bulb [UK IKEA]
3D Printed E26/27 "bolt" via Thingiverse or an old E26/E27 light bulb
Quick set concrete

Step 1: Terminology

Just a quick image so people know what I call things :)

There will be a couple of other plastic parts in the SEKOND light set such as a cable relief and a nut, which are not used.

Step 2: Hack the Lamp Fitting and Shroud

Use a hacksaw to remove part of the lamp fitting such that the flex can come out sideways. Use hot glue to hold the flex in it's new place.

Seal the holes, on the flex side of the lamp fitting, with hot glue and use electrical tape to cover the holes on the sides of the lamp fitting.

Cut a notch in the side of the shroud - there's a mark on the inside which you can use as a guide. I used a drill first then elongated it using side cutters. Note that you don't have to be very neat.

You don't need the cable gland, cable relief or the nut that fits the lamp fitting.

Step 3: Assemble

Annoyingly I forgot to take a picture of this step! If I make another I'll update this.

I designed a 3D printable bolt that mimics a light bulb base and provides a flange. This makes things very easy bt if you don't have access to a 3D printer then you could make something similar using hot glue, some wood/cardboard and a old light bulb that's had the glass removed - just be VERY careful as light bulb glass is extremely sharp.

Turn the shroud upside down and place the light fitting so it covers the large hole. Secure in place using the 3D printed "light bulb bolt".

Feed the flex out of the notch you made in the shroud. I used a piece of thin wire wrapped around the light fitting and then around the flex to hold the flex where I wanted.

Step 4: Concrete

Give the inside of the shroud a light coating of oil. I use ordinary machine oil on a rag, but any oil will do as it's a just acting as a release agent.

Mix the concrete according to the instructions - it should have a consistency of thick cream. Note that I used black concrete dye to darken my mix.

Pour the concrete into the shroud. Then flex/tap the shroud to get the majority of the air bubbles to the top.

Leave to cure.

Step 5: Finish

Once the concrete has set (typically 24hrs), undo the "bolt" and remove the concrete lamp from the shroud. Allow the concrete to fully cure, which I find is around 5-7 days.

Brush off any loose concrete (especially from what is now the underside) and coat the concrete in concrete sealer, wax, watered-down PVA or whatever else you have available. This is just to prevent it making dust as well as making it easier to wipe clean.

To stop the lamp scratching the surface it's placed on, I 3D printed a rubber base and glued it on using epoxy. But there's plenty of rubber feet available on eBay/Amazon that'd work just as well, as would craft felt or foam.

Fit a plug, screw in the decorative light bulb of your choice and enjoy :)