Moldmaking with Legos (Part 2)

For this project, I will be making a production mold for the smaller Celtic Ponies. This rubber mold will be used to make a simple two-part plaster medallion mold, one piece for the design and one piece acting as a “lid” across the flat back of the design.

To start, I will take my original and glue it to a base. In this case, I’ve used a 4×4 glazed tile because it separates easily from the rubber. Then I build a box around the design using Legos. To keep the Legos from sliding on the slick surface of the tile, I stick them down with double-sided tape (the kind used in scrapbooking). My Lego mold box is then filled with silicone rubber.

Normally I would key the back of the rubber, as I did in this post, and then pour a plaster base. The base keeps the rubber from distorting when it is clamped inside the mold boards. But here I’m not going to pour a base because I won’t be removing the Legos. They will act as my stabilizer instead. But I do need to pull the tile off and expose the negative of my design.

Now I have a negative image of my design, encased in Legos. My next step is to pour a positive image, also in rubber. I won’t pour just the design, though. I want to pour the design and the base – all in one piece – so that I won’t have to glue the design to a tile like I did in the first step. But to do this I need to box the area around the positive image, since right now that area is flush with the Legos. This is where the Legos come in handy because I can extend my box (in either direction) by adding more blocks.

Okay, so I’ve built my mold box up(side down) and I can now pour the positive piece.

This was the trick that it took me an embarassingly long time to discover. I didn’t have to take the rubber piece out and rebox it. I could just build the box up. Of course, I’m actually building the Legos upside down, but that works just as well. In fact, because Legos can be added to the top or bottom of my box, I never really have to remove them from the rubber. They can function as the stabilizer (eliminating the plaster back), and serve as a base to add mold box walls. And since the rubber is never removed from the box in which it is poured, the box never has to be re-sealed. (Resealing mold boxes is my least favorite job.)

I did key this one, and pour a plaster base, only because my kids were beginning to notice an odd shortage of rectangular Legos. Here I poured the rubber flush with the top (the dark grey Legos), cut the keys, added another layer of Legos, and then poured plaster.

(Bad plaster pour there – look at all my air bubbles!)

I have both a negative (inside the bottom half of the Legos above) and a positive (in the top half). I can now split the stack apart, and reveal my positive.

Now I have an original that gives, yet will hold up to repeated pours of plaster (the amber piece to the right). My negative (the light blue piece on the left) can remain in its Lego frame in case I ever need to pour another positive. In the next post I’ll use the new rubber original to make a working plaster mold.

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3 Responses to Moldmaking with Legos (Part 2)

  1. Hyn October 5, 2007 at 7:04 pm #

    Oh my God, Lesli, this is simply brilliant! Perhaps not as feasiable for a large piece, but definately very handy for smaller projects like this one! I’ve never heard of using legos before so I don’t think you are slow to pick up on it at all – I think you are quite clever!

    I use a small cardboard box, with oil clay and the original I am molding on one side so that it is in the middle of the box. Once I pour, I remove the original and the oil clay and it leaves me half the box to still pour into for the other side. Then I remove the cardboard box.

    Of course that method is fast and handy for me, but only works if I have boxes on hand I scan spare that are around the size I need! Otherwise I use a tupperware type plastic container to pour my smaller things into for the mold support.

    Thank you for sharing! This is the most interesting blog going in our hobby industry to me, at the moment. Keep it up! :}

    Paige Easley Patty
    Hanblechia Studio

  2. mel October 5, 2007 at 11:25 pm #

    OMG! I LOVE this stuff! Lesli, this is really cool info, and I am enjoying seeing the process. It is so much work, what you do. I am not at all convinced that you charge enough for your ceramics…

  3. Lesli Kathman October 12, 2007 at 12:40 pm #

    Oh, I cannot take credit for using Legos to make mold boxes, Paige. That tip came from Barry at Laf’n Bear. My “discovery” was simply that I could leave the Legos on the rubber pieces, eliminating the stabilizing plaster backing and making a ‘frame’ on which I could build (up or down) a new mold box as needed. I suspect that Barry may have already been doing this with his molds, since the idea is pretty obvious to anyone who has played with Legos a lot. Me, my main connection with Legos is cleaning them up from all corners of my house… so it took a little longer for me to figure it out! 🙂

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