Workshop

Silicone moulds and resin casting - June 9 2012


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Within this article, I explain the process and the techniques used for creating the site plan model for the Kings Cross Development. The model took 1 week as part of my Final year work at The Arts University College of Bournemouth. Further images can be found within my Portfolio.

 

 

The Brief 

For the unit: External Brief, I was required to find my own client and make a model for them based on their requirements. Although the mian focus was creating a 1:200 timber model for architects Maccreanor Lavington, I had a spare week within the project to make an additional model which would be a more experiemental model using different materials and processes to the timber one. Where as the timber model was focusing on the R5 plot of the development, the site plan model showed how the R5 plot sat in context to the rest of the site.

Starting out

I first made a MDF and styrene master. This was to act as a master to mould and cast. I was provided with architectural drawings for the site plan which I used to create the baseboard. I wanted to create an abnormal shape to the basic rectangular ones. The Kings Cross site offered an intersting enough shape so I used this.

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I also used these drawings to create the buildings. The buildings were to be block detail. The idea was that I would differentiate between them using different resins and translucencies. The building were made using MDF blocks.

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Moulding with silicone

The next step was to make a simple silicone block mould. I made styrene  box to hold the master in. Styrene is ideal for this as it is cheap, easy to cut and easy to attach, using dichloromethane. I plugged any hole with clay to avoid the silicone escaping. The silicone I used was supersil 25 which is a standard mould making silicone.

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To mix silicone, the required amount is weighed and 10% catalyst is then added. 

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To avoid air bubbles in the silicone, the mixed silicone can be placed into a vacuum former. This is done placing the mix in a drum and sealing the drum. As seen below, I did this by placing an acrylic block on the open top. Air is entered into the drum and once the silicone rises, the air can be removed. This can be repeated multiple times.

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The silicone can also be poured into the mould from a height, and into one corner. This method further improves that chances of avoiding air bubbles. The silicone will slowly fold over the whole of the master and fill the mould.

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The silicone will take approximately 16 hours to cure, however, an accelerator can be added to speed the cure time up. A thixotropic can also be added to the silicone. This is useful for different types of moulds and in this case it was not necassary.

Once the silicone has cured, the styrene mould and the master can be removed. It is then possible to cast various materials into the silicone mould. I wanted to try different resins to represent different buildings of the site.

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Casting with resins

Fast Cast is a Polyurethane resin which is a 2 part mix and takes aprroximately 10 - 20 mins to cure. The two parts are mixed equally (50:50). Before combining the the two parts, metal powders or pigments can be added otherwise the cured resin will be white in appearance. The image below is Polyurethane resin with aluminium metal powder added.

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Clear cast is a polyester resin and is translucent. It requires a 2% catalyst to cure. pigments can be added to achieve different colours and tints as seen below.


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I used a combination of fast cast and clear cast resins with different tints to achieve my final model.

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Final model

I made several different casts. Along with the master, below is an Image of the final casts.

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