Custom LEGO-Compatible Bricks!




About: depotdevoid is short for The Depot Devoid of Thought, the place where you go when you lo...

I've been working with polymer clay (FIMO, specifically) since I was about 15.  I always thought it would be neat to sculpt customized bricks to use with my LEGO and Megablocks sets, but I've been kind of stumped about how.  After much thought, several false starts, and some consultation with my little brother, I've come up with a workable solution.

This is a pretty cheap and fun way to make all sorts of specialized bricks for use with your building block sets.  They won't ever replace the core sets, as they aren't as regular as the real thing, but they can add some awesome elements and your own specific style to your creations.

Essentially, I made metal stamps the shape of the dots and depressions of the building bricks.  Polymer clay is wrapped around the dots or pressed into the depressions, and then baked.  Once cool, the stamp is removed, leaving either the desired dots or depression that will mesh with the standard building bricks!

Step 1: Gather Supplies

Here are some tools and materials you will need.

  • Liquid latex for mold making
  • Mold conditioning spray
  • Latex Caulk . . . maybe.  See step three for my misgivings about this.
  • Plaster of paris
  • Plumbing solder (higher melting point than electrical solder)
  • Polymer clay (I use FIMO out of habit, but Sculpey is cheaper and generally easier to find)
  • LEGO or Megablocks bricks that you don't mind getting a little messy
  • Wax paper
  • Aluminum foil
  • Cheap paintbushes (you WILL ruin them, so just go to the craft aisle at the dollar store and buy a couple packs)
  • A mixing container for the plaster, I used an old cool whip tub
  • An old metal spoon (also will be ruined)
  • Propane torch
  • Heat gun or hair dryer
  • Towel
  • Something pointy and metal, like an awl or a fine pointed screwdriver
  • Craft knife
  • Baking sheet

Step 2: Play With Your Bricks!

Pull out your building bricks (or your child's bricks, 'cause you're a grownup now and shouldn't be playing with toys), and build some forms.  These are eventually going to be cast in plaster, and have hot metal poured into the depressions.  Make one with dots up and another with depressions up.

I made a variety of hole sizes to try out.  I found that the 1x2 and 1x4 spaces made the best stamps, but all of them produced usable stamps.

Step 3: Make a Latex Negative

Latex mold making material and mold conditioner is available it most craft stores, it's around $25 bucks for the two combined.  I wanted to use pourable silicone, but I couldn't find any around town and (as so often happens) I didn't want to wait for shipping.  The latex is also a LOT cheaper than silicone.

Place a piece of wax paper over your work space--I used a board I could take to work with me.  With cheap paintbrushes, begin applying a fairly thin layer of latex over each of your molds, making certain to get into all of the nooks and crannies.  When done, apply heat and let it cure from white to tan, then add another coat. 

You'll need several coats (I went with around a dozen), so this could take some time.  Over the course of about three days, I did a coat in the morning, one at lunch, one when I got home, and another before I went to bed.  I left the molds in my car at work, the car was hot inside so everything cured quickly.

I'm not sure if this was a mistake or not, but after I had several coats on, I applied some latex caulk into the depressions.  I hoped it would make them stronger so they wouldn't distort when I poured in the plaster.  Unfortunately, it's a different type of latex and didn't bond properly with the mold material.  Also, it took a really long time (like two days) to cure and I think whatever solvents were mixed in softened the mold material, turning it white.  Everything worked out in the end, but I think I would use something else in the future, like a fast curing silicone caulk covered with another layer of latex.

Step 4: Remove and Prepare the Mold

Once everything is dry to your satisfaction, carefully peel off the wax paper.  Loosen the mold all the way around the edges, then slowly pull it out of the brick original.  If all has gone well, you should have a perfect negative of the building bricks!

Shake up your bottle of conditioning spray and apply a couple of coats, letting the mold dry completely in between.  The conditioning spray helps both to keep the latex pliable over time and to prevent sticking to whatever you're casting in it.

When dry, tape the molds into the bottom of a level waterproof container.  The one I used was a bit too small and slightly distorted some of the bricks, but it wasn't too bad.

Step 5: Cast the Plaster

Plaster of paris is mixed at a 2:1 plaster to water ratio.  The DAP stuff I bought is quick curing, so you only have a few minutes to work with it once you add water.  Fortunately, you'll just be pouring it into the latex mold.  Stir everything until it's even and pour, making sure to cover the entire mold at least 1/2 an inch deep.

Let it cure overnight to make sure it's all the way done, then remove it from the container.  Slowly peel back the latex just like before.  My plaster casts were a little uneven in spots, as the container was a bit small and not perfectly flat on the bottom.  If I were to do this over I would have built a little cardboard box of exactly the right size to do this in.

Still, when tested, both the dots and depressions meshed perfectly with LEGO bricks!

Step 6: Make the Metal Stamps

Wear eye protection!  This is a dangerous step, you could set yourself, your house, and your cat on fire if you're not careful!  Also, it's playing with fire, so it's fun dangerous!

Set yourself up in an outdoor workspace away from anything flammable.  Wrap the handle of an old metal spoon in a towel and use your propane torch to melt some plumbing solder into it.  Make sure it's lead free!  Use plumbing/metalwork solder because it has the highest melting point, meaning it won't get soft when baked in the oven with polymer clay.

When the metal is melted, use the torch to heat up the plaster cavity you're going to pour the metal into.  Switch back to the metal and make sure it's as hot as you can get it, then pour it in.  Once or twice while I was doing this the metal boiled and bubbled up splattering hot solder all over the place.  Wear goggles!

When done, wait for everything to cool down, then break the mold to remove the stamps.  Use a sharp implement to clean all the plaster out of the cracks.

Step 7: Make Your Bricks!

Okay, this is the really cool part! Once your stamps are all done, get your kids together and start building some custom, specialized LEGO-style bricks!

Press polymer clay into the stamps, then add more clay to flesh out the design, smoothing over the joins.  Get creative!  India and I built a whole bunch of these, then built an art gallery to house them in.

Bake the clay at a relatively low temperature, for a relatively short period of time.  The first batch I made, my clay was older and dryer and when I tried to use them with LEGO bricks they came apart.  The second time I used some clay softener and some new clay, and reduced the baking temp by 15 F and the time from 30 to 25 minutes.  The resultant bricks were flexible enough that they worked!

Finally, unless you had better luck with the metal casting than I did, you'll need to grab your craft knife and trim up the edges of your bricks.  My stamps are slightly irregular, so there were some bits of clay that had to be trimmed in each batch.

Step 8: Final Thoughts

The final step is to play with your home made bricks!

This was a whole lot of fun, and a realization of a very old DIY idea of mine.  The new bricks aren't perfect, they don't snap in as securely as the real deal, but they do work just fine.  I would like to find a material for the stamps that works better than the solder, and can be baked in the oven with the clay.  The stamps made from solder just weren't as perfect as I would like them to be, but I wasn't sure what other material to use.  Any ideas?

Thanks so much for checking out my instructable!  Please take a moment to comment, rate, and subscribe, also like me on Facebook!  I live for feedback from my readers, so make sure to let me know what you think!

Of course, the thing I most want is to see your own creations based on my instructable!  Post a picture in the comments of your own home made LEGO style bricks, and I'll send you a DIY patch and a 3 month pro membership!



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    46 Discussions


    Reply 2 years ago

    Wtf, Megablocks?? Who would vote Megablocks? I mean unless you are some weirdo or something. Probably the Jeffery Dahmer types. Lego is of course the one and only correct answer.


    6 years ago on Step 8

    I would take a look for a small book titled, "How To Cast Small Metal And Rubber Parts" by W. A. Cannon.
    Look on page 10 for Plaster Mold Casting . "A mixture of plaster, talc and water is poured around a pattern. (Take out the pattern)... , and the mold is baked in an oven to drive off moisture."
    I would guess baking at 200 degrees overnight would do it.
    This would prevent the solder from spattering.
    There are low temperature metals listed in the book as well.

    1 reply

    Reply 6 years ago on Step 8

    Nice, thanks for the recommendation! It's only ten bucks on Amazon, I may pick up a copy. I think I might find it useful!


    7 years ago on Step 6

    If the flawed castings were due to the solder solidifying too quickly, baking the plaster mold and filling it while it's still hot may help to slow down the cooling of the solder.

    1 reply

    Reply 7 years ago on Step 6

    Hmmm, I hadn't considered that. If I ever try this again, I'll go that route to see if I can thoroughly heat the mold before dumping in the solder.


    7 years ago on Introduction

    can you leave out the latex part because i can't find (cheap) latex in my local (craft) stores

    1 reply

    Reply 7 years ago on Introduction

    If so, you'll have to find a substitution--latex was the cheaper alternative to my original plan to use pourable silicone.


    Reply 7 years ago on Introduction

    Like, directly into oogoo? I tried casting it directly into LEGO, and it kind of worked, but wasn't usable with other bricks.


    Reply 7 years ago on Introduction

    yes. it is heat resistant enough to withstand a few seconds of molten metal, which is long enough to get a mold in. I'm not sure if it would be ideal for this, though, with all the small crevices. it doesn't stick to the metal and form a perfect model.


    7 years ago on Introduction

    very nice i wish i had thought of this when i was younger lol well at all for that matter

    1 reply

    7 years ago on Introduction

    so imake polmeyer clay then vacum form them to make plastic ones like the real ones