[Maker’s Note] Concrete Moulding: Reflections & Review

by Yun-Han Lin

Cement is a dry powder, often lime or calcium silicate based. It sets and hardens after mixing with dry ingredients and water. When it is mixed with sand and gravel, there is mortar or concrete; with different composition ratios, there can be different viscosity, fluidity, water absorption, etc. Some are suitable for installing ceramic tiles or moulding for walls, and some are applied straightly to the wall surface. With water and stirring, it can cure and be molded into various shapes. Also, the ingredients are not expensive and are easy to obtain. In recent years, it is very popular in DIY or hand-made projects where small flower pots or plates are made with cement. The following are a few molds we have tried and some tips for easy productions.

The concrete we use is mainly concrete mix for filling by Lotos, as you can tell by its name that it is made for moulding through filling. It becomes really fluid when mixed with water, so that it can fill every corner of the mold. Also, it is a bit absorbent, but the finished molds do not do leak a bit when filled with water. The fun part of using this cement lies in the choice of molds, as different containers may end up with unexpected shapes. As for the ratio of cement powder to water, it can range from 17 to 30 g of water, mixed with 100 g of cement powder. The more water, the thinner the mixture will be, where end products can come in more details and finer surface texture, yet it takes more time to harden. On the contrary, should there be less water mixed, it is suitable for molds in simpler shapes, which also harden faster.

Here are the cement works we built before, sorted in chronological order

1. Cement coaster: the work in early days when we tried cement work for the first time. When the cement paste is poured into the zipper bag, the bag gets inflated and the paste against the bag flows like water, making a smooth and glowy surface. It is not hard to make, which is suitable for parent-child activities.

2. Cement candle holder

3. Designer’s small plate: made using foam board as molds, as foam boards can be adjusted into any preferable shapes.

4. Cement clock: with a magnet embedded in the cement, the clock itself becomes a magnet. The numbers are designed to be movable, so that users can use other patterns or decorations to show the numbers.

5. Cement mosaic: it was the first time we used cement color dye by Lotos. We tried different color combinations and made a mosaic coaster.

6. Hexagonal lampshade: when filling hollow containers with cement, the most common container used is plastic cup as an outer mold. If the plastic cup is entirely filled with cement, it will become solid and there is no space inside left for the inner mold. Therefore, there needs to be a barrier to occupy the space for the inner mold in advance. We used clay once, and after the cement hardened, the clay within was removed, leaving a hollow cup. Yet, using clay as the inner mold causes many problems. For instance, the thickness of the cup was uneven. Later, we realized that we could use plastic sheets as a mold, and the cement should be applied to each face, and once face at a time. Check out our video for more details during the process!

7. Cement terrazzo calf

8. Mosquito repellent coil: the tricky part about this project is to make it as light as possible. An entire solid cement can be too heavy. Placing small objects as fillers in the mold when filling cement can help reduce both the amount of cement used and also some weight, just like the styrofoam beads stuffed in walls that are not meant to support weight in a building structure.

9. Geometric shape soap tray: this is our newest project, and we have not released the video of our making process. Foam sticks are used to build the outer molds for the intended tray shapes.

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