Make Concrete Garden Boxes PART 1 – Precast Form Build

Test Fit and Assembly

With pan head screws, assemble the form using the layout lines as a guide. Check that everything is square, fits tight, and there are no gaps.

Test fit and square all part assemblies
Test fit and square all part assemblies

If there are any variations with each assembly, you may need to try different part combinations to see what fits together best.

Label parts - garden boxes
Label parts

Label each mould assembly one through four. And also label each part assemblies with the corresponding base so you reassemble them the exact same way each time you use them.

Apply Finish

I apply several coats of Polyurethane Finish, lightly sanding between coats.

Apply 4 coats of polyurethane finish

I used four coats of this durable flooring finish. Wet cement is very corrosive so you want to protect the wood to get the most life from your concrete forms.

Pipes and Wire

Cut the PVC conduit down to length.

Wrap wire around pipe to reinforce concrete - cast garden boxes
Wrap wire around pipe to reinforce concrete

Also cut a 30″ length of stiff wire and wrap it loosely around the pipe. This will reinforce the concrete and give it strength where it is the thinnest.

Final Assembly

Cut a section of Concrete Reinforcing Mesh to size with small bolt cutters and have it ready to lay in the wet cement.

Cut wire mesh with small bolt cutters
Cut wire mesh with small bolt cutters

This will make the concrete panels very strong.

Shims to adjust overall panel length to 36\"
Shims to adjust overall panel length to 36″

This is where I remembered that not all 3/4″ plywood is fully 3/4″ thick. Most is now slightly undersized and I laid out the parts for actual 3/4″ plywood. It’s an easy fix by adding a few slim shims.

Add wire and pipes on final assembly - concrete garden boxes
Add wire and pipes on final assembly

Once assembled, the molds need to be made water tight. I use a small bead of Latex Caulking to do this.

Apply Caulking

Latex caulking to waterproof forms
Latex caulking to waterproof forms

Latex works well as it’s not overly strong and will allow you to disassemble the mold easily once the concrete sets up. Don’t use regular silicone for this. It’s too strong and will be difficult to remove later. Latex caulk is all that’s needed.

Level Forms

Level forms in both directions on secure surface - man about tools cast form mold concrete garden boxes
Level forms in both directions on secure surface

Place the moulds on a strong and secure surface and level them in both directions.

Spray with vegetable oil cooking spray
Spray with vegetable oil cooking spray

Once the caulking is dry, spray the mould with a releasing agent to keep the concrete from sticking. I used Vegetable Oil Cooking Spray for this.
UPDATE: Cover the pipe and pipe wrap wire with a cloth to keep the oil spray away from it during this step.

Continued on the Next Page

Shopping Cart
Scroll to Top