A concrete pendant lamp is a cast concrete shade suspended over a table or counter, and it is one of the more dramatic DIY concrete projects a homeowner can take on. The finished shade in the project that inspired this article weighs roughly 75 pounds, which means the form, the pour, and the hanging hardware all need to be engineered with that load in mind. Concrete is cheap, the tools are basic, and the process follows the same sequence used in any small cast concrete job: build a form, mix and consolidate the concrete, cure it, strip the mold, and finish the surface.
Designing the Form for a Cast Concrete Shade
The form determines the final shape, and a shade form is essentially a cylinder built from plywood circles and flexible paneling. The relationship between form surface and finished face is the same one that makes decorative concrete floor and wall tiles look crisp: smooth forms give smooth concrete, so the mold interior deserves the most attention.
The original build started with scrap plywood circles for the top and bottom, a melamine base for a clean release, and flexible wall paneling wrapped around the sides. The paneling bends around the curve without kinking and costs little enough to discard after a single pour.
- Scrap plywood for the top and bottom circles
- One sheet of melamine or plastic laminate for the base
- Flexible wall paneling for the curved sides
- Brad nails and silicone caulk to seal the form
- One 80 lb bag of concrete mix plus charcoal pigment
- Epoxy, screw hooks, cable, and ferrules for hanging
Cutting Circles and Building the Mold
Cut the top and bottom circles from scrap plywood with a jigsaw, clamping the pieces together so the cuts match perfectly. Screw the circles to a melamine or plastic laminate base, which releases cleanly, then wrap the sides with the flexible paneling held in place with brad nails. A disk sander squares up the edges of the form so the shade comes out even.
Wrapping and Sealing the Form
The paneling is flexible enough to follow the curve and cheap enough to throw away after one pour. Fill every nail hole and seam with silicone caulk so the concrete cannot leak paste through the mold, and clamp the seams tight while the caulk cures.
Why the Form Must Be Watertight
Concrete carries cement paste in suspension, and a leak lets that paste escape, leaving a weak, honeycombed surface. A sealed form also makes the mold easier to strip because nothing bonds through the seams and the paneling releases as one piece.
Estimating Concrete Volume and Mix Selection
Before mixing, calculate how much concrete the shade needs. An 80 pound bag of standard concrete mix yields roughly 0.6 cubic feet of wet concrete, and a concrete estimating worksheet and calculator helps you convert the form volume into bags so you buy the right amount instead of guessing at the register.
Concrete weighs about 150 pounds per cubic foot, which gives you a second way to sanity check the pour. If your form volume comes out to more than the bags you bought, stop and get more mix before you start; a shade cannot be poured in two batches without a visible cold joint.
Volume Math for a Cylinder Shade
For a cylinder, volume equals pi times the radius squared times the height. A shade that is 12 inches in diameter and 18 inches tall works out to about 1.18 cubic feet, which means two 80 pound bags with a little margin for waste. The finished shade lands in the 70 to 80 pound range, matching the weight that drives every hardware decision later.
| Component | Typical rating or amount | Role in the assembly |
|---|---|---|
| Screw hook | 150 lb rating | Main ceiling attachment |
| Hanging cable | 150 lb rating, 1/16 in | Suspends the shade |
| Cable ferrule | 1/16 in | Crimps and holds cable ends |
| Structural epoxy | 24 hr cure | Sets hooks into cured concrete |
| Concrete mix | 80 lb bag, 0.6 cu ft yield | Forms the shade body |
Pigment, Water, and Mix Consistency
Charcoal pigment added at roughly a quarter of the container per 80 pound bag darkens the cement paste without changing the strength. Mix water in gradually until the concrete holds together and barely slumps; too much water cuts compressive strength quickly and leaves a chalky surface.
Testing the Mix Before You Pour
Scoop a handful and squeeze. The mix should hold its shape, then crumble when you open your hand. If it runs, add dry mix in small amounts. If it crumbles immediately, add water a few ounces at a time until the paste coats every grain.
Consolidation, Vibration, and Air Bubble Control
Fresh concrete traps air, and trapped air shows up as pinholes on the finished face. Consolidating the mix is the fix, and the techniques used to consolidate concrete in congested reinforced members work in miniature: vibrate the form, tap the sides, and rod the mix as it goes in.
Knocking Out Air Bubbles
Mix the concrete inside the mold and vibrate the table or workbench while you pour. Tapping the form sides with a rubber mallet encourages bubbles to rise and pop at the surface, and working in small lifts instead of one big dump gives the air fewer places to hide.
Working the Mix Into Corners
Use a slender rod or a piece of rebar to work concrete into the bottom corners of the form. A shade has no reinforcing steel, so the paste has to fill every void on its own, and a void at the bottom edge becomes a chip the first time the shade bumps a wall.
Vibration Methods for a Home Shop
A handheld vibrator works, but a palm sander pressed against the form or a vibrating sander under the table gives the same result for a small pour. Vibrate in short bursts so the mix does not segregate, with the heavy aggregate settling to the bottom and the paste floating to the top.
Demolding, Curing, and Surface Finishing
The shade needs to cure before the mold comes off. Fresh concrete is not like new concrete over old concrete repair work, where bonding agents matter between layers; here the piece cures monolithically inside its form and then strips as one solid shell.
Stripping the Mold
The mold comes off with persistence. Remove the brad nails, work a pry bar around the rim, and pull the paneling away in sections. If the concrete sticks, tap the form gently rather than forcing it, and let the shade sit another day if it still feels soft.
Curing Time and Strength Gain
Concrete reaches roughly 70 percent of its final strength in the first 7 days and most of the rest by 28 days. Keep the shade covered and moist during the first week, then let it air dry before sealing. Hanging the lamp early risks chipping the edges while the concrete is still gaining strength.
Sealing the Finished Surface
A low gloss concrete sealer protects the surface from stains and moisture. It is optional on an indoor shade, but it makes the concrete easier to wipe down and deepens the pigment color, which is why most builders finish the piece before wiring it.
Sealer Options and Reapplication
Brush on two thin coats rather than one heavy coat, and reapply every couple of years if the shade lives in a humid room. Water based sealers clean up with soap and water and suit indoor fixtures, while solvent based sealers hold up better outdoors.
Hanging Hardware, Wiring, and Safety
Seventy five pounds of concrete hanging over a table demands rated hardware and a ceiling attachment into framing. The same concrete inspection and testing discipline used on structural elements applies here: check the cured piece for cracks, verify the hardware rating, and confirm the ceiling structure before you hang anything.
Rated Hardware and Load Calculations
Use screw hooks rated for 150 pounds each, three hanging cables, and 1/16 inch cable ferrules crimped at each end. Three cables share the 75 pound load, so the system runs at a fraction of its rating, which is exactly the safety margin a suspended fixture needs over a dining table.
Ceiling Attachment Rules
The hook must screw into the ceiling framing, a joist or solid blocking member, never into drywall alone. A 150 pound hook in drywall will pull through under a static 75 pound load plus any swing, and the result is a concrete block falling onto whoever sits below.
- Mark the joist location and pre-drill a pilot hole.
- Screw the hook fully into the framing until the threads bite.
- Crimp a ferrule on each end of the three cables.
- Attach the cables to the shade hooks and the ceiling hook.
- Test the assembly with a firm tug before releasing the shade.
Hanging With a Partner
Do not hang a 75 pound shade alone. One person holds the lamp steady while the other attaches the cables, and the extra hands prevent the shade from swinging into walls or people during installation. Crimp the ferrules, test the assembly with a firm tug, then let go slowly.
Strength, Weight, and Why Plain Concrete Works
Concrete is strong in compression and weak in tension, which is why structural engineers add steel where bending happens. The trade offs between prestressed concrete over reinforced concrete exist for beams and slabs, while a hanging shade works because the concrete is loaded in compression through the hooks and its own weight.
Compression and Tension in a Hanging Shade
The shade sits in compression along its own body, and the hooks carry the load through the epoxy and into the concrete. No member bends, so the plain mix handles the job with margin, and the shape stays stable for decades as long as the hardware and the ceiling hold up.
When to Call in Structural Design
If you scale the lamp up, mount it over a seating area, or hang it from a ceiling with questionable framing, treat it like a structural element and get the attachment reviewed. The math is simple, but the consequence of a failure is a heavy object falling, and that risk is not worth saving a consultation fee.
Start with a sealed form, consolidate the pour, cure the shade fully, and hang it from framing with rated hardware. The finished lamp weighs a lot, but built this way it hangs safely for years and becomes the piece of the room people ask about first.