DIY CONCRETE:: Umbrella Base

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.

Skill Level: Beginner

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

Tools:

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)

Concrete Mixing:

CHENG Outdoor Pro-Formula Admixture (Amber shown here)
100+ pounds Sakrete 5000+ Concrete Mix or equivalent
Rubber Gloves and Dust mask
Mixer / Wheel Barrow

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Step 1: Assembling the Form

Base Board:

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.

Center Pipe:

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.

Fix lamp shade to Base:

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.

Foam Strip Reveal / Kick:

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.

Bracing:

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.