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
madmanmoe646 years ago
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 :)

I want to see more pics

btw I did eventually get around to making this into a full concrete seating instructable. http://www.instructables.com/id/Modular-Concrete-Bench/
They look like those lego candie blocks XD
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?
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.
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?
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.
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.
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?

These are a few more pics I posted, You can see here how they interlock sideways.
dthorpe6 years ago
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 dthorpe6 years ago
i think the concrete is too heavy for silicone, think it just stretches the mold instead of just filling it up.
They usually use a firm urethane rubber for concrete molds.  Smooth-on.com probably has a video or two of concrete molding and stamping.
I used another instructable http://www.instructables.com/id/How-To-Make-Your-Own-Sugru-Substitute/ 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.
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.
venom15394 years ago
I thought stepping on plastic lego was bad enough.
Cam9184 years ago
This is unbearably cool. Tough for kids to play with, though...
XOIIO Cam9184 years ago
Not to mention breaking your fingernails trying to pry them apart.
MicioGatta4 years ago
thepelton4 years ago
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.
jtmcdole6 years ago
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
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.
Also, the pegs on the top of the construction blocks for sale here are slightly tapered.
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.
13near5 years ago
"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???
beerboyone6 years ago
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.
...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!
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.
or you could use mortar/thinset which has no aggregate.
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.)
tmr6 years ago
I love it I got to try it out
eblisster6 years ago
You could add concrete dye to this process and have a bunch of brightly colored ones.
Great idea. There are a lot of nice concrete stains out there to use.
minerug6 years ago
You should make inverted knobs on the bottom, so they work like lego blocks
Kiteman6 years ago
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.
you know i bet you wouldn't need mortar if you did that
lemonie6 years ago
Oh crikey! You're not planning to build a wall with these then? L
why wouldn't he they'd be stable
...provided there are spaces for the studs
Yes, spaces for the studs. But it would be great to build a wall eh? L
MJTH lemonie6 years ago
Ive always wanted a house made out of lego.
Ward_Nox MJTH6 years ago
funny you should say that one of the hosts of top gear (James May) is building one

robotguy46 years ago
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.
i know, except you might stub your toe on these.
This group had a machine which dry stacked with ribs/holes that looks like the exile castle but much more flat. the 'bricks' produced looked real nice.
gonzolo6 years ago
If you tap the sides of your mold with a hammer after you put in the concrete it will help eliminate the voids caused by air pockets. This will make the block smoother all over. Also using a trowel on the top to smooth the concrete will give all side a smooth finish.
With such large molds tapping it with a hammer isn't as effective, I found that you have to pick up the mold and rock it up and down, hitting it on the table, to get the smoothest finish. Or maybe I'm just impatient?
We pour 8" slabs and just hit the forms with a framing hammer and it does the job just fine. You're right in saying that it's probably just being impatient.
Our bricks were 35x35x22.5mm (14x14x8") and we didn't get it as smooth with a hammer, as someone else said, strapping an orbital sander on the edge is best.
Also, when you hit it with a hammer, hit it. Like you are driving in a nail, not just lightly tapping it. Found that out from 'holey' experience. ... At least if you have 'holes' in them, you can plaster over them with some morter mix after you turn them out of the mold.
But then I'd dent the lovely molds I spent days making :0 .
Yeah, I use a 22oz framing hammer on forms. They are usually made of 2x8s though. Just try to add some 2-by stock to the outside of your molds for extra support.
Using less water is a good idea too. It's called Dry Packing, where the concrete is just slightly wet. The only set back is with less water the finished product will not be as strong.
you could also take a small orbital palm sander and let the base vibrate against the edges of the forms to get out a lot of the voids and bubbles in the form.
strmrnnr6 years ago
I to have a couple suggestions for getting rid of the voids. One method is to use a vacuum chamber. I am also starting to experiment with Tesla's vacuum/pressure technique. Another method is the vibrator that the construction people use. Ask your Mom to borrow her personal messager - Make sure you get all the grit off before you give it back. Always keep your tools clean and ready to use next time.
TheEyrie6 years ago
Awesome, what a potential! Just the thing for a slumping housing market! How long do you think it'll take to build this?
Probably a few days, not to long. I mean, come one, its only about 5000 pieces.....
Depending on your dedication ;)
AdHd TheEyrie6 years ago
Depends. Are you going to make the bricks on-site (inside the Deathstar), or make them elsewhere and haul them to the Deathstar? Of course, if you maike them on-site you have cleanup issues. Decisions, decisions...
well one id make fiberglass bricks for making that and 2 you'd need to make more than just the basic brick
beerboyone6 years ago
also you could apply some oil to the form before pouring to help release.
I used WD-40 it's easy to apply, soaks into the wood and it less likely to pool in the mold and interfere with you're concrete,
It helps to coat the mold with polyurethane paint or some other 'smooth' primer and paint. Then use a mold release like a thin coat of vegetable oil (motor oil works too, but not as 'green'. Big commercial molders put vegetable oil on their forms as a release these days. But make it a 'thin' coat.
Check out this stuff, it is kind of expensive...but it works perfectly for this application, and it is CA VOC compliant.
Oil is a bad idea, I used it in a mold I had it then had poor concrete that crumbled before and after curing, I use a mold of PVC and Plexiglas to make concrete donuts for sprinkler systems, I prepare the mold by placing it in water and then then removing it and immediately pouring my concrete mixture into the mold, I use a quikrete mixture that has fibers in the mix to allow for strength without all the large aggregate getting in the way. I plan to make a new mold soon and publish it.
JTWAIT6 years ago
Instead of using a piece of wood with holes, and then breaking it apart carefully; you could just use a piece of Styrofoam instead. Making it easier for removal. Also there are concrete dyes available.
Alx_xlA6 years ago
Where's the photo of the finished product?
If you use blown clay gravel, the kind you get to put in the bottom of flower pots, instead of the standard gravel, the block will be a lot lighter.

Also, sticking the block on a vibrating table would get rid of all air in the mold.


What if you had used short plastic containters - 6 of them - under the plyqood one the front then pressed into the back side so that you'd have matching raised nubs and indented nubs so that the blocks could be stacked? (like those short plastic deli containers....) I don't know much about concrete so I dunno if this would be strong enough to stack - but its a thought.
bwomp996 years ago
I saw a lego-type design used at Pompeii, I guess it was a Roman thing:


This is how Romans fixed their pillars of stone together to stop them slipping sideways. It's where we took the inspiration for our bricks.
kevinhannan6 years ago
Hi, This is a brilliant project, one which I'm going to do next summer for my (now 2yr old) granddaugther. I hope you don't think I'm hijacking this project but as it's related does anyone know where I can make/get the molds for the "summer circle" patio, *please*? Apologies if this is in the wrong place; I'm still new here. kind regards Kevin
mechcem6 years ago
I the background near the end of the movie Time Bandits there are piles of giant stone Legos
Joyusnoise6 years ago
any kind of motor with something attached slightly offset on it's shaft attached to the mold will vibrate causing the fill to settle, I've use a 12 volt starter motor and it works OK just can't run it for long periods of time ( it heats up)
heathbar646 years ago
this is a really cool idea. If you notice in madmanmoe's picture of his form, the pegs are slightly tapered. this is good, since it will release from the mold easier, and will wedge together with the other blocks.
TnT1016 years ago
Justa few helpful hints
Sand wood mold/smoother=EZer release and/or
coat with wood sealer. I was told PAM cooking spray helps too.
To have smoother concrete use edge of a palm or orbital sander against wood frame to vibrate air pockets out. AND for smaller project (due to cost) use ROCKITE expansion cement. You can mix it to milkshake consistency for less air & dries in like 20min
BigAl676 years ago
I like the bricks from the old "Exin" castles. I have always fantasized about scaling up the bricks, making them from Beta-Styrene concete and building a full size castle to live in. If you have never seen Exin castles (from the 1970's) you have to do a google search and check them out. Since it's been 40 years and the company is long since out of business there probably isn't any intellectual propety issues (certainly no patent issues as those would have expired long ago).
mrpickles26 years ago
Good Day. This is very interesting. Maybe if I use concrete Lego blocks I could actually get my two kids to give some help building things outside! A VIBRATOR is likely the way to go for reducing the voids. When they pour huge concrete parts they use an industrial vibrator on a long cable to get air out. They simply lower the thing down into the wet concrete and move it around as they pour. At home we could use... well a vibrator if one is around, remember to wrap that rascal so it doesn't get concrete all over it. Another possible device would be a back massager in a plastic bag? I'm sure that others will have ideas too. Also though I'm no concrete expert, reducing the size of the aggregate in the mix or adding some sand might help too. Really cool idea!
madmanmoe646 years ago
I also posted these other pictures of our, similar, build. If anyone was interested
jtmcdole6 years ago
you could use ratchet straps or some other clasp instead of nails all around.
jbrecken6 years ago
I think something went wrong with your measurements. There's too much margin around the outside of the raised circles for it to look like a real Lego brick. The distance from one of those circles to the edge of the block should be half the space between the circles, so that if you placed two blocks next to each other the circles would be evenly spaced. It seems like you accidentally reversed that relationship and used twice your spacing for a margin.
GorillaGrill (author)  jbrecken6 years ago
=) I'm afraid you're right.
It was made in sort of a rush as a birthday gift for my mother.

Good eyes there. =)
I suspect you want to learn the LDU and scale up in those... A good unit for lego stuff.
dchall86 years ago
I agree with the others. If these truly interlocked, you might have a marketable product.
SinAmos6 years ago
Your main problem is that you didn't use the bottom mold. Your lego won't work with other legos it's size.
pobzeb6 years ago
You have the form for the top of the block, but the bottom is still flat. You need a way to form the bottom of the block so that they can be stacked.
Focker6 years ago
omg! If you made these fully functional lego blocks I could totally build a sweet house. . . or castle or. . . . (wanders on into legoland)
nruegs Focker6 years ago
you'd probably only have to add a lid to the mold, with holes in it just slightly larger than the nubs on the top. Although, if you were to do that, you might want to design a box that is able to be taken apart and put back together easily and repeatedly, as it sounds like you'll be making a lot of these. And rightly so.