This is a minimalist vase for one tall flower, built out of concrete and wood.

The three essential functions of a vase are revealed by this clean and sleek design: (1) to provide a stable base, (2) to hold some water and (3) to support the flower.

In addition, this vase can be hung on the wall.

To add some coolness in the making process, Lego is used to build the concrete mold.

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Step 1: Study, Blueprint and Needed Stuff

Blueprint

Using a wooden tulip to figure out what the size shall be, I first made a design in LibreOffice Draw in order to choose a shape and determine aesthetic proportions.

Needed supplies

1. Concrete (fine-grained)
2. Iron mesh (or iron wire)
3. Oil
4. Concrete repair putty
5. Concrete sealant
6. Nail polish (or waterproof lacquer)
7. Paint, matte finish (preferably spray can)
8. Wood bar (width must fit 2xN Lego)
9. Steel string (0.8 mm thick)
10. Bead and small nail
11. Epoxy glue
12. Paper glue
13. Paper (or felt)

Needed tools

1. Lego bricks
2. Plastic box
3. Masking tape
4. Hot glue gun
5. Spatula
6. Sanding paper
7. Miter box
8. Pliers
9. Concrete drill bit
10. Carpenter square
11. Clamp
12. Drill press

Step 2: Building the Mold

Chamber

Build two bases at a time, by creating two six-bricks-tall, 7x7 chambers.

Cavity

The central cavity is created by a five-bricks-tall, 3x3 column.
It turned out to be a bad idea to use Lego for this, as it is very difficult to demold without damaging the Lego pieces.
Instead, I would now use some styrofoam.

Anyway, the column is held in place by some 8x2 plates.

Step 3: Building the Mold (2)

Grove for the wood piece

A 8x2 plate, covered by flat plates, is hot-glued to one side of the mold.
You should cover this piece by masking tape in order to ease the demolding.

Edges

The four inner edges are made rounded, using some concrete repair putty.

Base

Place the mold in a plastic box or flat plate, and tighten it with a few hot glue drops.

Step 4: Shaping the Iron Armature

Reinforcement

Using iron mesh, build a cage that will fit inside the concrete wall.

If you do not have mesh, you can use some iron wire and create a square spiral.

Step 5: Spreading Oil

Evenly spread some oil on all surfaces that will touch the concrete, in order to ease demolding.

Step 6: Adding the Concrete

Mix the concrete to a creamy consistency.
Pour the bottom layer.

Place the iron reinforcement.

Place the column.

Add more concrete to fill the mold to nearly the top.

With a screwdriver or a stick, insure that the concrete fills all edges and corners.

Step 7: Waiting...

You must now be patient and resist the temptation to demold before at least 48 hours.

Step 8: Demolding

Carefully detach from the plastic box or plate.

Peal off the Lego bricks.

Remove the inner Lego column. I had to damage these bricks in order to remove them, so, as said in step 2, better use e.g. styrofoam, which can be torn away with no regrets.

Step 9: Rectifying

With sandpaper make the top side even.

I wanted to keep the concrete rough character, hence only fixing the biggest surface defects (most of them occurring during demolding) with concrete repair putty .

Step 10: Sealing

Apply concrete sealant on all surfaces, and let dry.

Apply two or three layers of nail polish in the hole, in order to make it perfectly waterproof.

Step 11: Painting

Apply several layers (approx six) of spray paint. Each layer must be thin, so that the concrete roughness still appears through.

The last 3 layers were sprayed at a 60 cm distance, in order to leave a very matte surface.

My final finish has a very matte surface, showing off the concrete character, as well as some Lego brick marks.

Step 12: Making the Stem Holder

Stem holder

With the pliers, bend the steel wire to form the illustrated shape.

In order to avoid the sharp bends to break, insert a piece of wire while folding (see picture 4).

Glue a small bead at the end of the wire.

Wood bar

Cut wood to size, sand.

With a drill press, make two small blind holes (approx 1.5 to 2mm ø) to insert the stem holder, which must stay in place by itself, upon moderate pressure.

Make an approx 4mm ø hole for hanging.

Optionally apply some wood primer to protect it.

Step 13: Assembly

Scratch off the paint in the grove receiving the wood.

Carefully make a blind hole (3 mm deep) towards the top of the groove, for anchorage.

Pin a short nail into the wood, at the position of the blind hole. The nail head should stay out by 2mm. The nail may have to be shortened so that it does not cross the wood.

Mix some epoxy, fill the blind hole, and spread a thin layer on both the concrete and wood sides.

Clamp together with a square to insure perfect wood vertical alignment.