Project:Geopolymer Chess Figures

ProjectInfoBox Chess Figures

Status:	in progress
Release Date:	christmas time- maybe
Initiator:	Airlag
Materials Used:	styrene foam, silicone rubber, alkali activates silicates
Tools Used:	sharp knife, drying oven
Approx. Cost:	about 80 €

This is my first project I'm doing in the CoMakingSpace for real. I thought about a few other projects but those never made it past the thinking and sketching part.

A few months ago I stumbled over some information about Geopolymers in the internet:

and several more. (In this context it is irrelevant whether it is historical correct if the pyramids were partly build using concrete or not)

The recipe varies from website to website. Wiki explains that there is a wide variety of ingedients that can replace each other. Therefore I started my own experimental research with available or easily accessable materials.

One of the ingredients is soda lye (NaOH). This chemical is corrosive.

The materials and chemicals aren't expensive. The most expensive is definitely the silicone rubber.

Portland Cement Free Concrete

Trial 1

the activator:
6g H2O
add 4g NaOH slowly because the chemical reaction produces heat
add 25g sodium silicate

the aggregate: 185g sand (unknown origin, turned out it contained lots of limestone)
add 100g Zeolith powder

add the activator to the aggregate

Zeolith is a relatively cheap mineral. I ordered some powder. I got granumate instead. I tried anyways.

The resulting mixture was in no way pourable. I tried to pack it, then I let the chemistry magic do its job.

After a week it was hard but porose and crumbly.

Trial 2

the activator: same as above
6g H2O
add 4g NaOH
add 25g sodium silicate

the aggregate:
200g tuff powder (tuff is old vulcanic ash) 100g white sand from a pet shop

add the activator to the aggregate

The resulting mixture looked like moist sand but was very squashy. The mixture was not pourable.
After a week it was still moist and squashy.
Baking it in a drying oven at 80°C for 3 hours turned it to a rock.
After another week I discovered that the reference body shows some cracks.
Several weeks later it seems to sweat out some kind of nearly white powder. The cracks seem get smaller.

Trial 3

the activator: same as above just 4 times more of it
24g H2O
add 16g NaOH
add 100g sodium silicate

the aggregate:
200g tuff powder
100g white sand

add the activator to the aggregate

The resulting mixture is creamy but still not pourable. However, I tried this mixture for a first atempt on the chess figures (see below).
This time I put it immediately into the drying oven at about 60°C for 3 hours. The resulting reference body seemed hard but it isn't entirely. Hitting the edge of a table caused a dent in the reference body. One week later nothing has changed. The reference body is as durable as chalk.

The Chess Figures

I want to make chess figures out of liquid stone.
For this I need casts.
To make casts I need prototype figures.

I decided to use styrene foam and a penknife to create my prototypes. I had some square meters of 5mm panels lying around. So I used that material. It's very easy to cut but it's hard to carve tiny details. The material tends to crumble if you don't use the sharpest possible knife.
I wasn't satisfied with the first set of figures, so I made a second set.

Next I created small boxes for each figure out of the same material. I glued one figure to the bottom of each box, then I poured silicone rubber in the box. Two hours later I removed the box and cut the silicone rubber in half. After removing the remains of the prototype figure the reusable cases for the stone figures are finished.

I didn't make much pictures. Shame on me. I only have this picture of the first set of prototype figures.

Figures Trial 1 from Material Trial 3

Material Trial 3 seemed promising enough, so I poured it as good as possible into the silicone cases. The material was creamy, not liquid. So I ended up with several bubbles. The horse has no chin. The queen broke in half. Anyways, it's the first attempt. So here are the results.

And then I threw them away. Next try will be better :-)