Concrete LEGO




How to make your own 10:1 scale LEGO brick out of concrete!

You'll need:
  • 4 - 5 liters of concrete (when mixed)
  • Some scrap wood
  • Saw
  • Hammer and nails / screws and screwdriver
  • Ruler (or something else to take measures)

Step 1: Messure Up!

So, how large is a LEGO block?

These links ought to give us some clues..:

To make a 3 x 2 brick we get the following measurements:
Height of block: 9.6 mm
Width of block: 15.9 mm
Length of block: 23.8 mm
spacing of knob centers: 8 mm
Diameter of knobs: 5 mm
Height of knobs: 1.7 mm

To scale this up, we just change "mm" to "cm". Easy, huh?

10:1 block:
Height of block: 9.6 cm
Width of block: 15.9 cm
Length of block: 23.8 cm
spacing of knob centers: 8 cm
Diameter of knobs: 5 cm
Height of knobs: 1.7 cm

Step 2: Building the Frame

Remember that you want to be able to disassembly the molding box after the concrete has set, so dont go overkill with the size of the nails. (Or, just use screws instead)

1) Start out with a peace of wood that is approx. 18 x 26 cm and drill out the six 50 mm holes using a hole saw.

2) Nail another 18 x 26 cm peace of wood to the underside of the previous one.

3) Add the 96 mm high walls to complete the jig for molding.

Step 3: Molding

1) Follow the instructions on the bag of the concrete on how to make the proper mix. You will need at least 4 liters.

2) Fill the box up.

3) Why not add a copyright infringing logo to the wet concrete?

4) Set aside for a few days or what ever the bag of the concrete states, in order for the .

5) Carefully remove the box, starting with the sides and the "bottom".
To remove the wood with the six holes, its easiest to try to break the wood apart. Carefully.

6) If you chose to paint it, use the proper paint!
Candy red would probably look sweet!



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    95 Discussions


    6 weeks ago

    How about mini legos? You can even build a house out of those?


    9 years ago on Introduction

    I was surprised to see this as, for the past couple of months, I've been working on a seating project similar to this. We had a budget and lot longer for development (we also had copyright issues to avoid) But I thought people might like to see what we did. We had to consider durability, mass production and re-use of the molds. I have hundreds more pictures if anyone's interested. Obviously these look slightly different to actual LEGO bricks but they stack properly :)

    12 replies

    btw I did eventually get around to making this into a full concrete seating instructable.


    Reply 9 years ago on Introduction

    Beautiful work. If they were rectangular they would be able to lock across blocks better/have more diverse use. Maybe make those in addition to these?


    Reply 9 years ago on Introduction

    Yeah, that would be cool. we didn't need the blocks to overlap for this project, but longer bricks would allow you to make more sound structures, if you wanted.


    Reply 8 years ago on Introduction

    There was a reply here I DID NOT POST (but it had my screen name). Anyone else have a problem with having their screen name hijacked?


    Reply 9 years ago on Introduction

    Your mold seems to have the same shortcoming that I noticed in the original. You seem to have the same spacing from the raised squares to the edge of the block as you have between the squares. If the outside margin was half the space between the squares, then you could stack your blocks in staggered rows, like a regular brick wall. Although it would mean you'd also need to make a mold for a half-size block if you wanted to make a rectangular wall, so maybe that's why you didn't do it that way.

    DUDE!!! I am going to do this to make a fire pit!!! I have been trying to decide how I wanted to construct it and I didn't see anything compelling. The custom concrete block design is awesome.


    Reply 9 years ago on Introduction

    We did consider this (lots of design meetings and eventually decided against it), but the idea was to make abstract seating arrangements and not a large brick wall. Plus (I won't explain why) offsetting the lugs in that way makes producing the molds more complicated.


    Reply 9 years ago on Introduction

    I don't know about stacking "properly" — the first principle of LEGO building is "cross your lines" (that is, offset each row relative to the one below it so you don't have vertical interfaces running more than one row high through your structure). It doesn't look to me like these blocks can even do that, because the studs are too close together in the center and not close enough to the sides. Still looks like a neat project though!

    I like this version a lot. Looks very clean, sleek. Do you have a link to more pictures? What about tinting the concrete? And if you did build a mold that was interlockable sideways like bricks then use a lighter weight material like hypertufa maybe for short walls? Could be good for making raised gardening beds?


    9 years ago on Step 3

    To prevent the concrete from sticking to the form and make it easier to remove the form after the concrete is set, line the form with a sheet of plastic. Hefty garbage bags might suffice, or a bit of visquene sheet. Fold the sheet carefully in the corners to minimize unsightly creases in the concrete. To make a lot of these blocks, you should probably invest in making a few silicone molds instead of wood. They'll be more work and more expensive to make than wood, but should be much easier to pull off the concrete and should last longer.

    4 replies

    Reply 9 years ago on Step 3

    i think the concrete is too heavy for silicone, think it just stretches the mold instead of just filling it up.

    just pick a nameDeus

    Reply 8 years ago on Step 3

    They usually use a firm urethane rubber for concrete molds. probably has a video or two of concrete molding and stamping.

    I used another instructable to make stepping stone molds from a plasticene over Styrofoam original. The 'oogoo can be layered on even after the base coat dries on the mold and if you are worried about stretching and strength, you can put fibreglass drywall tape down as you lay up the mold. The modelling clay original easily pops out of the silicone mold. This was an easy & inexpensive way to make unique stepping stones for a fundraiser. Btw those cement legos are awesome!


    the easiest way to keep cement from sticking to the forms is to cote them with diesel fuel. when working with a local contractor we always had diesel in a five gallon bucket and used a paint brush to apply.