Prosthetics - Master mould, part 2! Fibreglass jacket

After the silicone mould has been made, the next step is to create a fibreglass jacket. This will support the mould and help it keep its shape when it is being used. 

Figure 1 - Fibreglass jacket (Brown, J. 2020)

Fibreglass is a reinforced plastic material that is embedded with glass fibres. Fibreglass is supplied as a flattened sheet called strand matt, which comes in different grades (or thickness) from 300g to 600g. When this is combined with resin, it creates a very strong, durable composite. (Fibreglassdirect, 2017). This process is also known as laminating. 

Fibreglass can be used for an array of different things, not just in prosthetics. For example, it is used widely in the automotive industry, in cooling towers, mining, the chemical industry and more. The properties of fibreglass makes it useful in all these areas. It is a good electrical insulator, it is incombustible, doesn't rot, has low thermal conductivity and has high mechanical strength. (Phelps, no date). Fibreglass is also extremely light.

Figure 2 - Example of Fibreglass used in other industries (Bug, D. 2020)

Fibreglassing is done in two stages. The laminating process with the strand matt, and a gel coat resin that creates a smooth outer layer. In mould making for prosthetics, the gel coat is done first so that it is nice and smooth inside the jacket for the silicone mould to sit in.

Figure 3 - Silicone mould inside fibreglass jacket (Brown, J. 2020)

Gel coat resin is a high quality isophthalic resin, which is water resistant and has UV light stability. (Neillsmaterials, no date). It is a three part mixture of the resin, the catalyst and pigment. The resin is clear, and the pigment is optional, but it helps to add it so it can be seen where the resin has been placed. 

The mixing ratio for the gel coat is 1% - 5% of catalyst. The less that is added, the slower the gel coat will set and vice versa. The artist used 300g of gel coat resin, and used 3% catalyst. The amount of catalyst used was 9g. This is worked out by taking the amount of resin used, dividing by 100 to get 1%, then multiplying by 3 to get 3%. So 300g/100=3g, 3g x 3=9g. To add pigment, each brand varies for how much should be added, but for the one that was used, 10% pigment is required. This is 10% of the resin AND the catalyst. 309g of resin and catalyst, divide by 10 results in 30.9g of pigment. This was rounded up to 31g.

This mixture is then applied to the silicone mould and surrounding board using a paste brush. A polywax mould release must be applied to the board first however, as it will be impossible to separate the two afterwards. 

Figure 4 - Gel Coat layer (Brown, J. 2020)

This stage was quite simple, aside from working out the measurements. The main thing to be mindful of is making sure that everywhere is covered in the gel coat and that there aren't any spots missing. This is then left to set for 20 - 45 minutes under appropriate extraction/ventilation.

The next stage is the laminating layer. This was done with 300g grade strand matt and polyester resin. This process can be quite difficult and can take many years of practice. Air bubbles can get trapped when laminating around corners, so it is important to take special care to try eliminate these. 

Polyester resin is a two part mixture of the resin and the catalyst. The ratio can be between 0.25% - 3% of catalyst. Due to this process being fairly tricky, a 0.5% ratio was used, to keep the setting of the resin slow. As this was being used for a half head mould, 1.2kg of resin was used. To work out how much catalyst to add, 1.2kg(1200g) divided by 100 equals 12g (1%). 12g divided by 2 equals 6g (0.5%). So 6g of catalyst is added to 1.2kg(1200g) of resin. 

This was then applied on top of the gel coat in three layers. The artist worked section by section, to avoid applying too much in some areas but also to be able to keep on track with where they have already applied the fibreglass. With this being a new process to them, and with having sustained a previous shoulder injury of their dominant hand, they did work very slowly, resulting in the resin beginning to set before they finished. The final layer was done the following week, using 300g of polyester resin and 1.5g of catalyst. 

Going forward, if this is to be done again, the artist knows to start off with a smaller amount of resin and mixing more if it is needed, to avoid wastage. 

The artist's gel coat was very smooth which is perfect to fibreglass over. However, if the surface was considerably lumpy or uneven, part of the mixed polyester resin can be decanted into a separate bowl and mixed with talc. This will create a paste that can be applied first to smooth it out before going in with the fibreglass.

Figure 5 - Freshly released Master mould and fibreglass jacket (Brown, J. 2020)

Figure 6 - The mould inside the jacket before sanding (Brown, J. 2020)

Figure 7 - The jacket after sanding (Brown, J. 2020) 

Figure 8 - Inside of the jacket (Brown, J. 2020)

As seen in figure 5, fibreglass can look very messy, but it can also be extremely sharp. Therefore it is very important to neaten up the edges and get rid of any sharp points poking out.

Looking at the COSHH sheet for polyester resin, which can be read here, this is a very dangerous substance to be working with. It produces flammable vapours which are very harmful if inhaled, can harm unborn children and can cause damage to organs over prolonged or repeated exposure. Therefore it is of the utmost importance to be wearing the correct protective equipment. The artist was supplied with a Tyvek Classic Xpert coverall, which creates an "effective barrier against dust particles and liquids in fibreglass and composite manufacturing". (Cfs, no date). They were also given a Gerson 9000E2B vapour respirator, which offers "effective and comfortable protection against certain gasses, organic vapour and particulate hazards found throughout industry". (Cfs, no date).

The COSHH safety sheet for the gel coat (see here) also states that this is harmful by inhalation and is irritating to eyes and skin, so the same precautions were taken here as well. Safety goggles and a double layering of gloves were included in both of these safety precautions. 

Figure 9 - The coveralls and respirator (before application of goggles and gloves) (Brown, J. 2020)

Overall, this process was quite lengthy and a little tricky. The fibreglass came out well for a first try, though it could be done better through practice. In future, less of the polyester resin will be mixed to begin with, as it is now known that the artist will work slower, and the resin may set before it is all used, even with a lower percentage of catalyst. 

-Jess

References:

• Clear gel coat and catalyst. (no date) Available from https://www.neillsmaterials.co.uk/product/clear-gel-coat-and-catalyst/ [Accessed 03/01/2021].
• Fiberglass - Types, Properties, and Applications Across Industries. Available from https://www.phelpsgaskets.com/blog/fiberglass--types-properties-and-applications-across-industries [Accessed 03/01/2021].
• Gerson 9000E2B Series Respirator. (no date) Available from https://www.cfsnet.co.uk/acatalog/Gerson-9000E2B-Series-Respirator-OMAA2P_001.html#SID=8443 [Accessed 03/01/2021].
• Tyvek Classic Xpert Type 5/6 Coverall Large. (no date) Available from https://www.cfsnet.co.uk/acatalog/Tyvek-Classic-Xpert-Type-5-6-Coverall-Large-OOVTYV-001.html#SID=8607 [Accessed 03/01/2021].
• What is Fibreglass or Fiberglass? (2017) Available from https://www.fibreglassdirect.co.uk/blog/post/what-is-fibreglass-or-fiberglass [Accessed 02/01/2021]. 

Bibliography:

• 450g Emulsion Bound Chopped Strand Mat (1000mm). (no date) Available from https://www.easycomposites.co.uk/450g-emulsion-bound-chopped-strand-mat [Accessed 02/01/2021].
• Campbell, A. (2018) Electrical Insulator. Available from https://energyeducation.ca/encyclopedia/Electrical_insulator#:~:text=Electrical%20insulators%20are%20materials%20with,flowing%20where%20it's%20not%20wanted. [Accessed 03/01/2021].
• Catalyst mixing ratio. (no date) Available from https://www.cfsnet.co.uk/acatalog/methods_mixingcatalyst.html [Accessed 03/01/2021].
• Debreceni, T. (2019) Special makeup effects for stage and screen: Making and applying prosthetics. 3rd ed. Abingdon, Routledge. 
• Fibreglass Car Panels. (no date) Available from https://www.grplite.co.uk/racing.php [Accessed 03/01/2021].
• Gelcoat application for open moulding. (2017) Available from https://www.fibreglassdirect.co.uk/blog/post/gel-coat-application-open-moulding [Accessed 02/01/2021]. 
• Gel coat application guide. (no date) Available from https://www.fibreglast.com/product/Gel-Coat-Application-Guide/Learning_Center [Accessed 02/01/2021]. 
• How to make a fiberglass mold. (no date) Available from https://www.bottompaintstore.com/blog/gelcoat/how-to-make-a-fiberglass-mold/ [Accessed 02/01/2021].
• Isophthalic. (no date) Available from https://www.merriam-webster.com/dictionary/isophthalic [Accessed 03/01/2021].
• Pease, S. (no date) Fibreglass Manufacturing Process: Laminating. Available from https://www.stuartpease.co.uk/manufacture/laminating [Accessed 03/01/2021].
• Polyester Brushing Gelcoat / Flocoat. (no date) Available from http://www.mbfg.co.uk/user/datasheets/GelFlobrush_msds.pdf [Accessed 03/01/2021].
• Polyester Gelcoat. (no date) Available from https://www.fibreglassdirect.co.uk/polyester-gelcoat.html [Accessed 02/01/2021].
• Safety Data Sheet. (no date) Available from https://www.sherfab.com/assets/images/LILLY%20RAM%20W-1%20WHITE%20%20GELCOAT%20%20SDS.pdf [Accessed 03/01/2021].
• Safety Data Sheet, Polyester resin. (no date) Available from https://www.tetconnect.com/images/stories/virtuemart/documents/POR002_SDS.pdf [Accessed 03/01/2021].
• What exactly is GEL COAT? (2006) Available from https://forums.ybw.com/index.php?threads/what-exactly-is-gel-coat.88767/ [Accessed 02/01/2021]. 
• What is fiberglass? (no date) Available from https://polser.com/en/frp/what-is-fiberglass [Accessed 02/01/2021].
• Zyk, S. (2016) Making a simple fibreglass mould using green tooling gelcoat. Available from https://www.youtube.com/watch?v=syAmF65iGlU&ab_channel=SolbooZyk [Accessed 02/02/2021].

Figures:

• Figure 1 - Brown, J. (2020) York College.
• Figure 2 - Bug, D. (2020) Making fiberglass body panels Ep.1 Roof mold. Available from https://www.youtube.com/watch?app=desktop&v=hew_5NXkaAw&ab_channel=DougBug [Accessed 03/01/2021].
• Figure 3, 4 - Brown, J. (2020) York College.
• Figure 5, 6, 7, 8, 9 - Brown, J. (2020) York College.