Laminate Casting into Brush-On Mould

Laminate Casting into a Brush-On Silicone Mould
By Paul Carnall
A M T Composites

In this project, we did not show you how to make the mould as this is too advanced. Instead, we used a pre-made silicone mould to cast a hollow object – a Moroccan Wall Sconce Lamp – using a brush-on, light-weight, laminate technique with a sandstone finish. Please contact Paul Carnall at AMT Composites on 011 392 4232 if you wish to attend a workshop on more advanced methods of silicone mould making.

Requirements for Laminate Casting

  • Ready-made brush-on silicone mould
  • Material One (M1 – laminate resin)
  • Silica sand
  • 150g Triaxial woven glass fabric
  • 50mm paint brush
  • 80 gritt snad paper
  • mixing container (non-pourous)
  • Wooden spatula for mixing silicone

Instructions for Laminate Casting

This method of casting is ideal for products that need to be hollow, like the Moroccan Wall Sconce Lamp. Simply casting resin into mould (as in the block mould project) would not produce a usable part. So, instead of casting into the silicone mould, a lightweight laminating technique was used.

Step 1: applying a decorative “Gelcoat layer” into the mould

  • Material One liquid and powder is mixed according to instructions on products. (Using a shear mixer on a variable speed, hand held drill works well). Once the M1 is mixed, silica sand is added until a “thick paint” consistency is achieved (600 grams of mixed M1:400 grams of fine silica sand)
  • A thin layer of this mixture is then painted into the mould (be careful not to miss any spots). This layer is referred to as the “Gelcoat layer” and will become the decorative sandstone finish on the outside of the lamp.

Step 2: reinforcing the Gelcoat layer

  • Once the Gelcoat layer has become touch dry (about 20 minutes) another batch of M1 is mixed. This time no sand is added. Triaxial woven glass fabric is cut to size then placed into the mould over the Gelcoat layer and wet out with M1 using a 50mm paint brush. The glass fabric should be completely wet through with M1. Two layers of glass fabric should be more than adequate to offer a strong lightweight laminate.

Step 3: allow to cure and demould

  • The M1 laminate casting can be carefully demoulded in 40 – 50 minutes at 23C but will only reach full cure in 24hrs.Step 4: neaten and trim
  • Once the decorative wall sconce has been demoulded, a light sand with 80gritt sand paper will neaten and clean up the edges.