Cut melamine board to create side pieces & bottom of form. The side pieces should be the thickness of the melamine board plus the thickness you want your countertop to be (our side pieces were 2 1/4″ because we wanted a 1 1/2″ thick counter).
Cut side pieces to length so that they form a square around the bottom, two of the sides will be the same length as the side of the bottom where they attach, the other two sides will be 1-1/2″ longer so that they overlap the other two sides.
Drill holes 3/8″ up from the bottom edge of the side pieces to attach them to bottom of form, also drill holes in the ends of the sides which are longer than the bottom.
Line side piece along the edge of the bottom piece and pre-drill holes thru so the wood doesn’t split.
Put in screws and screw together.
Repeat with all 4 edge pieces.
Wipe inside of form to remove any saw dust.
Place painters tape around inside edge leaving a gap big enough for a bead of caulk. (Concrete can react with silicone changing the color of it, the tape keeps any smeared caulk off the inside of the form, leaving just the thin line along the edge.)
Caulk along the inside edges, going up along the corner seams too.
Smooth out the caulk with your finger to remove any excess and round the corner.
Let caulk dry according to directions on tube.
Once dry, remove tape, make sure to pull tape back toward itself not sideways.
Set the mold on a flat surface and make sure it is level.
Coat the inside (bottom & sides) of the mold liberally with olive oil (this is to keep concrete from sticking).
Add water a little at a time and mix until the concrete is about the consistency of oatmeal. (You don’t want it too watery as that can make a weaker counter.)
Pour concrete mix into concrete mixing tub.
Pour concrete into mold, it should be about half full, and smooth out.
Once smooth, use an orbital sander along the outside edge of the form to vibrate the mold – this gets air bubbles out.
Place the wire mesh (cut so that there is a 3/4″ gap between it and the sides of the mold) in the center of the mold.
Mix more concrete and place over the mesh. The concrete should be level with the top of the mold.
Smooth out and repeat the step with the orbital sander.
Using a 2×4, firmly press the board across the top of the form to smooth and level the concrete, this can get a bit messy.
Let dry for a couple hours, then go over the concrete with a trowel to help smooth it out.
Cover with plastic and let dry according to the directions on the bag. We let ours dry for 3 days.
Once dry, remove the screws from the form and pull off sides (they will stick a little from the silicone).
Carefully lift the concrete top to it’s side and pull away the bottom.
Sand off any rough edges.
We let ours dry for another day outside of the form.