Jesmonite Casting

Jesmonite is a gypsum based composite that when mixed with an acrylic polymer, cures as a solid form with a plaster-like appearance. The original product was developed in the UK in 1984 as a safer alternative to fibreglass. It has numerous applications in full scale architecture and across the creative industry.

Why use Jesmonite?

  • Stronger than plaster and more impact resistant
  • Replicates fine details from the mould with less chance of breaking
  • Easily mixed with different colours
  • Quick drying. Casts can be de-moulded within short space of time. Full cure/strength takes 24 hours.
  • Solvent Free meaning less harmful to the environment and safe for use inside the workshop or studio environment.

As students of architecture Jesmonite offers you the same advantages as full scale building application giving it uses at a wide range of modelling scales and types.

After using it at Atelier La Juntana Summer School we thought we’d have a few experiments ourselves. Mixing at the standard ratio of 2.5:1 we have carried out several tests demonstrating how pigments can be added to create varied effects depending on your requirement. Whilst we currently hold a limited stock of the standard AC100 Jesmonite, it is readily available from 4D with your student discount.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Marble, Stone and Granite, Terracotta red brick and Concrete effects are easily achieved by mixing in paints, lacquers or different aggregate types such as sand. Metal effects can also be achieved using metal powders.

A really great and safe to use casting product – get casting!

 

Low-Melt Metal Detail Casting by Jana Kefurtova

Jana explained her project for us:

The 1:10 detail fabrication was my first-ever casting exercise and definitely one of the most exciting tasks I have been involved in throughout my architecture course. It required a lot of preparation and careful planning of each step, but I was extremely happy with the outcome and I would repeat it if I had a chance. The key to success was to understand the casting process and plan the whole procedure beforehand.

Firstly, I modelled the hinge in SketchUp and tweaked it several times to make sure it was water-tight for 3D printing. After it was printed, I added an additional layer of acrylic to increase its thickness in certain areas, which was necessary for creating the mould. This step could have been avoided, had I known better how the mould was to be created. As I learned, it is definitely worth carefully checking your 3D model with the staff before printing. You do not want to 3D print repeatedly due to the relatively high cost of the process and unavailability of the printers during busy deadline times.

Next step was a fabrication of the mould, which was to be as tight as possible in order to save the material (silicone). When pouring the silicone, I did not mix it well enough with the activating agent, which caused it not to dry properly overnight. Luckily, it was still possible to save the mould by additionally mixing more activating agent into, and the whole mould came out really well in the end.

The putrid pouring was probably the simplest step of the whole process, however, there were still lessons to be learned. The mould has to be fixed together very tightly with clamps, as the hot metal is unexpectedly expansive and it will push your two halves of the mould apart. I repeated the casting itself twice, as the first piece was not perfect. This did not require any additional material as the first cast was simply melted.

The metal hinge was then integrated into a sectional model of a timber door to show its function. This was another part of the model-making task, which took almost as much time as the casting itself. One of the unique aspects of this exercise was that apart from the putrid and silicone, I only used scrap material from the workshop: acrylic, timber, plywood and MDF. This significantly reduced the price and proved that almost every piece of material that a student disposes in the workshop can be used further by someone else.

Working with metal left me being amazed by its strength and heaviness combined with plasticity and the ability to be shaped into very fine details. It might seem like a challenging material to handle, but it is in fact incredibly fun and fascinating one. I would recommend casting to anyone who wishes to add something bold and unique to their project.

– Jana Kefurtova 2016

Designing the Mould

When it comes to successful casting the work is all in the design of the mould. There are many considerations to have that require some reverse engineering in your mind before being able to pour the first cast correctly. In this case as Jana was creating her cast detail from scratch she had to first make the detail the the correct scale in order to have the mould be created around it. This was done using a combination of an ABS 3D print and some laser cut elements.

Due to the final cast being in metal a suitable silicone for high temperature casting is essential.

Here are some key considerations when designing a mould:

  • The mould should always be designed to use a minimum of casting material (in this case the expensive heat-resistant silicone) to ensure you are getting the most from it without having to overspend.
  • How are you going to pour material into the mould?
  • The mould must also consider the cast removal – Will the cast piece come out in one? Does the mould have to consist of multiple parts? If so how can we effectively locate these parts to ensure an accurate cast?

Metal Casting Jana Kefurtova (4)In Jana’s case it was decided that the mould could be created in two parts. In order to do this the master model had to be suspended in the middle of the mould casing to allow the first half to be poured. The support piece that was used to suspend the piece would also serve as the pour hole once the mould was ready to be used. In addition to the overall shape of the mould casing Jana also added two location ‘lugs’ which would allow the mould to fit together exactly. These lugs were in place until the first half of the mould had cured before being removed to allow the second half to create the positive part of the lug.

Before pouring the second half of the mould it is important to add a release barrier to prevent the two halves sticking together. In this case a spray wax coating was used but there are several products available for the job. Metal Casting Jana Kefurtova (5) Metal Casting Jana Kefurtova (9) After the second half is cured the mould can be taken from the casing and any overlaps in the pour can be hand trimmed and removed ready for casting.Metal Casting Jana Kefurtova (10) Low Melt Metal Casting

Once the mould has been trimmed and cleaned of any foreign matter you are ready to cast. To ensure the cast is easily removed from the mould it is necessary to lightly dust the mould halves with talc.

Metal Casting Jana Kefurtova (12)Suitable casting metal can then be broken up and melted using a melting pot. All equipment and elements used are specifically for casting purposes and you should always be sure the products are suitable for the job you are attempting.

ALWAYS WEAR HEAT RESISTANT GLOVES WHEN WORKING WITH HOT METAL AND EQUIPMENT!Metal Casting Jana Kefurtova (13)

Once the metal is completely molten in the melting pot it is then time to fill the mould using a suitable ladle. In this case it was necessary to have an extra pair of hands to support the mould whilst pouring.

Pouring in one smooth action will help to get the best quality cast. In this case it was necessary to pour three times to fill the mould. This is not idea but due to the working time with the molten metal the cast was crisp and consistent after a second attempt. (A key benefit of this material is that any failed attempts to cast can simply be broken up and re-melted to be recast meaning little waste material) Metal Casting Jana Kefurtova (17) Allowing around 15 minutes to cool is important so as not to distort the metal when trying to remove it from the mould in a soft state. Metal Casting Jana Kefurtova (20)The competed cast piece was then hand finished before being added to Jana’s functioning detail model. The moulds made for this project and the resulting detail model are currently on display as part of B.15:ARCHITYPES on the first floor of our building.

Metal Casting Jana Kefurtova (21) Metal Casting Jana Kefurtova (23)All equipment and material used here is available from 4D with your student discounts.

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Plaster Casting guide inspired by Timothy Richards Models

Earlier this year myself and Jim went on a visit to Timothy Richards workshop in Bath. Read more about that visit here.

In response to what we saw there we decided to have a go at casting some facade tests of our own to demonstrate to you the potential when using this method for modelmaking. Starting with some reference images of the University of Manchester Archway we decided to focus on one of the Gothic style windows as our subject.

Making a ‘Master’

Initially recreating the form of this stone work in miniature may seem time consuming but as you will see the end results are fantastic and the intricate detail featured is easily replicated by casting.

A good way of creating details like this is by layering sheet material, in this case acrylic. Planning the layers on CAD will allow you to break down the details into manageable  stages (Above). When combined, the layers of laser cut acrylic form the recesses and steps in the winder with the radius in the stone work being replicated using a filler and hand sanding (Below).

Spraying a coat of primer paint on hand finished areas can help to identify any imperfections in the surface (Below). This primer can then be sanded back

The extra details of the window can be formed using styrene and or abs strip with any further radius being creating again with filler. Once complete the master model is ready to be moulded. 

 Pouring a Silicone Mould 

The are a wide range of silicone’s available for mould making so it is always advisable to check the specification of individual products before committing to use them on your master model. Firstly ensure the master is secured to a mould former – in this case we used a storage try which suited but bespoke formers are usually required.

Ensure the silicone is mixed to the manufacturers instructions and pour in a thin stream to avoid any air bubbles forming against the master mould. Ensure the master is sufficiently covered and allow to cure for the recommended time.

Once cured carefully remove the silicone mould preserving the master mould to be reused if any problems occur. The benefit of using silicone is that the flex allows the master and eventually cast items to be easily removed without much stain on the items themselves.  Some minor trimming of silicone overlap may be required before the mould is ready to be used for plaster casting.Plaster Casting

As with the silicone there are many types of plaster available so always check to see if the specification suits your needs. In this case we simply used stone plaster mixed to the correct consistency and poured directly into the silicone mould – no release agent required.

Once the plaster has set it can be carefully removed from the mould giving a completed cast. These sections can be used as tests or replicated to create a more detailed facade. 

One area we have touched on is adding pigments to the plaster mix to give varied results in terms of finished cast colouring. We will revisit this area when we have time to experiment some more and let you know how it goes. If you have any ideas that could make use of this method of making be sure to get in touch either via email or in person at the workshop. We are more than happy to help! Scott & Jim

 

 

Timothy Richards: Fine Plaster Architectural Models, Bath

Last week, my self and Jim took some annual leave to go on a modelmaking road trip! We visited two main locations and so I’ll split this summary up into two posts. Firstly, this post will cover our visit to a graduate friend of mine’s place of work in Bath.

Timothy Richards has become the world leader in the production of fine plaster cast architectural models for exhibition display and private commission.

Over the past few months there have been several student projects attempting to delve into the plaster casting medium to convey their ideas.Whilst we have some experience of this process we thought it would be useful to ourselves and to upcoming students to give an insight into this process commercially and how better than to visit this master of the art!

A friend of mine, Lauren Milton, with whom I graduated in Modelmaking is now working for Tim and was able to give us an extensive private tour and insight into the workings of the company. Tim’s models range from complete buildings to facade’s and architectural details. Many of these models are made to order as private commissions however there is a range of popular works which are kept in stock for purchase.

The method used to produce the models has been refined over time but essentially involves creating a ‘master’ form of the subject to take a mould from then casting in the appropriate coloured plaster which can be pigmented to suit. One of Tim’s core beliefs about model building is that a model should be as similar in materiality as the building it represents. This means that all of the works produced here are cast in their final colour and therefore no paint is used on the cast surfaces. The only areas where colour may be applied is again through a ‘raw finish’ material such as thin sheet metal used to emboss over certain areas much as they would be in reality on roofing details etc.

Once cast, the building or facade components are assembled and any additional details such as window frames and railing are added. These details are primarily made from etched brass – a process we will cover in another post but in the mean time please ask myself or Jim for more information.  The resulting components can be made extremely fine and add a great deal of realism to these models.

Finely sculpted elements are made by sculptors who are paid to create exact replicas of organic details on the buildings. Once complete the scaled down sculpts are cast in white metals and then added to the master models before being cast into the final model.

Tim keeps everything for future reference meaning an extensive store of past model masters and moulds. This area in particular is fascinating and shows the breadth of experience compiled through sheer number of past projects in store. This visit was truly fascinating and insightful. It may be possible for us to arrange a lecture and demonstration from Tim this coming academic year. Should this happen I can’t recommend it enough!

For more on Tim’s work click here: http://www.timothyrichards.com/

Outside of our workshop visit we spent some time looking around Bath looking at some of its fantastic architecture and the historic Roman Bath house. All in all a great place to visit should you get the chance!

Taking from our visit we have decided to have a go at creating some plaster models of our own so we’ll keep you updated on our progress with that in the coming weeks.

Scott