This is a super simple project that has been a huge hit. Here's a quick overview. Check it.

Our nephew wanted a TechDeck half-pipe for his birthday this year. We thought we'd kick it up and build him his very own real concrete fingerboard bowl park. The goal was to create a unique park from materials we had on hand. At 60 lbs., this park weighs a wee bit more than our nephew.

Materials:
tub/form (we used scrap 3/4" plywood and spray glued some plastic film to it)
bowl(s)
caulking
styrofoam
ready-mix concrete
spray silicone or some type of mold release
and of course, duct tape

Step 1: 1. Create the Form

Create a negative mold of your desired park shape.

We built a tub from scrap 3/4 plywood and spray glued some plastic film to it. To create the bowl shapes, we used 1 larger wooden bowl and 2 smaller glass bowls. The transitions/gaps where shaped from a few chunks of styrofoam and duct tape.

Note: The mold needs to be smooth, so the concrete can release when cured.

We used caulking to make smooth transitions and rounded corners. Use your finger and a little water to smooth out generous beads/globs of caulking. Let the caulking dry overnight before pouring concrete.

Step 2: 2. Pour Concrete

Mix and pour the ready-mix concrete.

We used a full 60lb. bag of basic post concrete mix since we had that on hand. It worked ok, but cracked because the form was too thin (specs state minimum of 2" thick). The trick to a smooth final finish to knock all of the air bubbles out. We tamped everything well with a small stick. Then we beat on the outside of the form with a hammer. You will see the bubbles rise to the surface. Let sit for at least 24 hours. (we rushed it and cracked the main bowl. as an easy fix, we glued the pieces to plywood with liquid nailsback in business)

Step 3: 3. Remove Form

Carefully remove your form. If you have any cracks or bubbles, fill with non-sanded grout or other concrete patch/filler.

Add the finishing details like:
-stickers
-coping
-rails
-extensions
-etc