Introduction: Concrete LEGO

Picture of 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!

Picture of 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

Picture of 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

Picture of 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!


happilysane (author)2016-08-04


madmanmoe64 (author)2009-07-29

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 :)

CottonMG3338 (author)madmanmoe642014-12-04

I want to see more pics

madmanmoe64 (author)madmanmoe642011-08-12

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

XOIIO (author)madmanmoe642011-08-11

They look like those lego candie blocks XD

thebriguy (author)madmanmoe642009-08-10

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?

madmanmoe64 (author)thebriguy2009-08-10

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.

thebriguy (author)madmanmoe642010-02-07

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?

jbrecken (author)madmanmoe642009-07-29

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.

RichardBronosky (author)jbrecken2009-07-31

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.

madmanmoe64 (author)jbrecken2009-07-29

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.

JoeStrout (author)madmanmoe642009-07-30

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!

random-charm (author)madmanmoe642009-07-30

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?

madmanmoe64 (author)random-charm2009-07-30

These are a few more pics I posted, You can see here how they interlock sideways.

dthorpe (author)2009-07-30

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.

Deus (author)dthorpe2009-08-02

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

just pick a name (author)Deus2010-01-29

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!

jake14 (author)just pick a name2012-01-30

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.

vatosupreme (author)dthorpe2009-07-30

Another Idea would be to paint the mold with Krylon or epoxy paint. When dry, then spray the mold with WD 40 or Pam or some kind of cheap oil that will act as a release. Good project.

venom1539 (author)2011-09-01

I thought stepping on plastic lego was bad enough.

Cam918 (author)2011-04-28

This is unbearably cool. Tough for kids to play with, though...

XOIIO (author)Cam9182011-08-11

Not to mention breaking your fingernails trying to pry them apart.

MicioGatta (author)2011-03-13


thepelton (author)2010-10-28

One way I just thought of to make the pegs on the top and the sockets on the bottom slightly tapered would be to use paper cups to form them, since such paper cups are normally tapered from lip to bottom.

jtmcdole (author)2009-07-29

The only problem I have with this is you can't stack these. If you duplicated the base board and used the hole-saw plugs (lining them up with their respective base holes), you could then leave a long-edge open, frame up the box, and fill from the side. Then you'd have cup's and pegs for stacking

aldefork (author)jtmcdole2009-07-31

I agree, you could also use perlite instead of gravel in the concrete to make them lighter (I have not tried this with concrete but made a furnace using bricks made with it) I suspect the true lego proportions would have to be modified a little to enable concrete stacking.

thepelton (author)aldefork2010-10-28

Also, the pegs on the top of the construction blocks for sale here are slightly tapered.

thepelton (author)jtmcdole2009-07-31

There is a company here in Colorado Springs that makes concrete building blocks in a similar method. They use holes that are slightly larger than the pegs, so they don't snap together like Lego blocks, but can be stacked into a nearly permanent (short of a hurricane) structure.

13near (author)2009-11-21

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

beerboyone (author)2009-07-28

After you pour you should pound on the outside of the form with a hammer. this would get a lot of the voids out and you'd end up with a smoother block. or use a concrete vibrator (vibrator for concrete not made out of concrete) if you have one.

mikeasaurus (author)beerboyone2009-07-28

...also there are different types of concrete with various levels of aggregate, for a project like this (one that doesn't require much strength) you could use one with less aggregate which will also produce a smoother look.
But if nothing else, you must vibrate (tamp, hammer) your pour afterward.

Looks great though, super fun!

hassi (author)mikeasaurus2009-11-04

Do a search for "papercrete."  Uses paper as an aggregate and reduces weight significantly.  There's a jillion recipes and your simple search will yield good results.

Green too:  Less concrete and waste paper (card board, corrugated, news print, cartridge paper, you name it...

A GRAND idea, these blocks...

"you could use one with less aggregate which will also produce a smoother look. " Or you could just use smaller aggregate in your concrete mix. You could also use a high performance / lightweight concrete mix to get the smooth look with a very high strength.

Mike__ (author)masterfishslayer2009-07-29

or you could use mortar/thinset which has no aggregate.

servant74 (author)Mike__2009-07-30

Finding lightweight concrete would work. Even the 'Sackcrete' has it. Or use pumice or vermiculite for the aggregate. You can also make the concrete 'greener' if you reduce the cement 10% and add the same amount of flyash. But it will also slow the hardening of the concrete. I have been doing some casting of concrete lately, lining the mold with 'rubber' and oiling (vegtable oil is a 'green' answer here) the forms helps. The rubber gives it a very smooth surface, if you use a mix that is a little more 'soupy'. (Don't just add water, ask your local concrete company about the chemicals they have that can help. If they are nice, they might sell you a little bit or give it to you.)

tmr (author)2009-08-18

I love it I got to try it out

eblisster (author)2009-07-30

You could add concrete dye to this process and have a bunch of brightly colored ones.

thebriguy (author)eblisster2009-08-10

Great idea. There are a lot of nice concrete stains out there to use.

minerug (author)2009-08-08

You should make inverted knobs on the bottom, so they work like lego blocks

Kiteman (author)2009-07-28

LOL, I knew James may would find a way to cheat!

It would be more accurate if you pressed another wooden former into the concrete in the main mould, to make the brick hollow and stackable.

A whole wall of these would be awesome.

Ward_Nox (author)Kiteman2009-08-07

you know i bet you wouldn't need mortar if you did that

lemonie (author)2009-07-28

Oh crikey! You're not planning to build a wall with these then? L

Ward_Nox (author)lemonie2009-07-28

why wouldn't he they'd be stable

Ward_Nox (author)Ward_Nox2009-07-28

...provided there are spaces for the studs

lemonie (author)Ward_Nox2009-07-28

Yes, spaces for the studs. But it would be great to build a wall eh? L

MJTH (author)lemonie2009-07-28

Ive always wanted a house made out of lego.

Ward_Nox (author)MJTH2009-08-07

funny you should say that one of the hosts of top gear (James May) is building one

robotguy4 (author)2009-07-29

Finally a Lego brick that you can't hurt yourself on when you step on it! One thing: someone should build in a connecting system on the bottom (like actual Lego. Not just holes on the bottoms) I wanna see a house made out of these.

An Villain (author)robotguy42009-08-03

i know, except you might stub your toe on these.

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