This Instructable will show you how to make a concrete umbrella base from an IKEA lamp shade using basic tools and materials. The lamp shade is relatively cheap and makes an attractive concrete mold that can be re-used for dozens of castings. The size of your umbrella will determine the diameter of the pipe that gets cast into the concrete, and also the overall size of the base. For larger umbrellas or gusty spaces, you'll want a larger umbrella base that weighs about 100 pounds. The smaller lamp shade makes a base that weighs about 60 pounds.
There are four steps in this Instructable - Assembling the Form, Casting Concrete, De-molding, and Finishing.
Materials and Supplies:
- IKEA Melodi Lamp Shade or similar plastic container
- 3/4" Plywood (approximately 16" x 16") for Base Board
- 3/4" Plywood for Bracing
- 2" Galvanized Pipe with Floor Flange OR PVC pipe (Actual size is determined by your umbrella pole.)
- 1" x 3/4" Foam Strip 50" long, covered in clear packing tape
- 100% Silicone Caulk
- Modeling Clay
- 2-1/2" Hole Saw and Drill
- Screw Gun
- Pre-Drill and Countersink Bit
- 1-1/4" Drywall Screws
- Hack Saw or Angle Grinder
- Concrete Polisher (optional)
Step 1: Assembling the Form
- The first step is to make the base board. A piece of 3/4" plywood works well, cut to 16" x 16" or just larger than the outside diameter of the lamp shade.
- Draw diagonal lines to find the center point. Use a 2 to 2-1/2" hole saw to drill a hole through the base for the pipe to pass through.
- Take a piece of galvanized pipe, 10" to 12" in length, and screw it to the bottom of the base board using a floor or ceiling flange. The galvanized pipe should be centered in the 2.5" hole.
- If you're using a length of PVC pipe, cut a hole that's as close to the outside diameter of the pipe as possible for a very tight fit.
- Cap the top end of the pipe with a piece of styrofoam or insulating foam and clear packing tape.
- Put some modeling clay on the flat side of the lamp shade as shown. Slide it over the galvanized pipe and press it down onto the base board. The clay will help seal the bottom of the mold and keep concrete from getting underneath the form and lifting it up during casting. A thick bead of silicone will also work, but it's messy and the caulk gun won't fit down into the lamp shade.
- Put a bead of 100% silicone around the outside edge of the form where it meets the base board. Be careful not to bump and dislodge the form. The silicone will cure in a few hours and help hold everything in place.
- Creating a reveal at the bottom of the piece will help prevent chipping as the concrete is dragged around. This is one of the trickier steps, but it's not completely necessary.
- Cut a long strip of 1" insulating foam and cover all sides with clear packing tape. Use spray adhesive on one side and work the foam strip around the top edge of the form. Without the tape, the foam won't make such a tight bend and will snap. Trim down the excess so the edges meet up.
- Without some bracing, the form could float up or get knocked over during casting. Cut two boards that are the height of the lamp shade plus 3/4" for the thickness of the base. Screw them into two sides of the base board. Cut a third board to tie those together from the top, this board should be tight with the top of the form, helping hold it in place. Screw on the top board and the form is ready for casting.
Step 2: Casting Concrete
- Clean the inside of the form with soapy water and remove any debris.
- Add decorative aggregate, inlays, or other decoration using spray adhesive. This piece had a little bit of decorative aggregate and a stone inlay on the top surface. It's subtle but it looks nice.
- Wear rubber gloves and a particle mask.
- Add 120 pounds of concrete to a wheel barrow, plus the Outdoor Pro-Formula. Mix until it's a uniform color.
- Add about 1 gallon of water and mix with a shovel or concrete hoe. Continue mixing for about 5 minutes and add water by the cup until the mix reaches the right consistency.
- Avoid a soupy mix! The ideal mix will have some body and you can hold it in your hand. Too much water and it will be running through your fingers. Too little water will make the mix gritty.
- Place the form on a level surface.
- Fill the form with concrete. Don't fill it all the way to the top! Fill it about half way up the foam strip. Leaving a gap will help the concrete drop out of the form later.
- Pick up one edge of the form an inch above the tabletop and drop it repeatedly to help the air bubbles rise to the surface. Tapping on the sides of the form will also help, but be careful not to dislodge the form.
- After the form is filled, cover it with plastic. This will help keep the humidity in the concrete and minimize cracking.
- Leave the concrete to cure on a level surface, out of direct sunlight for 3-4 days.
- A temperature of 60 - 80 Degrees Fahrenheit is perfect.
Step 3: De-Molding
- Unscrew and remove the flange from the base board.
- Remove the base board.
- Remove the foam strip by digging it out with a flat screw driver.
- Flip the mold over, place the edge of the mold on a board and gently drop it until the concrete is released.
Step 4: Finishing
- Saw off the galvanized pipe with a hack saw or grinder.
- Polish the top with an orbital polisher.
- Fill any air pockets with a color-matched slurry.
- Install furniture feet on the bottom of the piece by drilling small holes and fixing them in place with epoxy. This will help eliminate damage to flooring from dragging the umbrella base around.
- Drill a hole in the center of the concrete for drainage.
- Sealing outdoor pieces isn't necessary, but it will give them a nice shine and help keep them looking good for a long time.
- Check out the Sealing Concrete Countertops and More Instructable for tips on the sealing process.