Hello All,

I have been doing some resin casting for a few months and have mainly used preset reusable (purchased) moulds. Having gone as far as I can with the moulds I have I decided to step things up a notch by learning how to make my own moulds and thereby greatly extending my repertoire.

I am using "DSM Water Clear Polyester Casting Resin" that requires a 1-2% Part B activator.

I have used an "RTV Silicone Mould Making Rubber 1kg Kit" to make my test mould. I have one mould completed, a wrist bangle. This worked as expected and it is a great mould.

My casting process is as follows;

1. Use a scale to get the weight of Part A after removing the weight of the measuring cup. This gave me the amount of Part B to use in my mix.

2. Add some pigment colouring to my Part A and then add the Part B.

3. Stir well and for at least two minutes.

4. Pour the resin into the mould carefully, making sure to 'squish' some of the resin around the mould to get complete coverage. Allow for a little excess to sit over the gap at the top of the mould.

5. Mark the time of casting (as a reference) and then leave to set.

The Problem

Here's the rub. While my resin cast sets it takes MUCH longer than any previous cast (into an open mould). In fact, while the deliberate overspill sets and the cast can be demoulded it remains tacky. Even after almost two days free standing.

I have tried increasing the Part B in an attempt to offset any influence from the pigment and the lack of oxygen getting to the mould, but still no joy. I even theorised that the mould was drawing away any thermolitic heat (needed to assist the cure process) and increased the Part B to almost twice the necessary measurement. Still no joy, the piece comes out of the mould tacky and remains that way.

I tried testing the cast by simply letting it set in the measuring cup (including the pigment) and that is fine, it set's perfectly, so it's not the mixture or the pigment.

It has to be something with the mould, but I am out of ideas for now.

Has anyone else experienced this. Has anyone else played with creating their own silicone moulds and what success did you have?

Thanks in advance for any help you can give, it's greatly appreciated.

Des

I have