A Sticky Resin Problem

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

I tend to use epxoy resin rather then polyester (fewer nasty fumes!), but have you tried putting the pieces in a warm place eg an airing cupboard? This has helped me to get my pieces to finish setting.

It's worth having a look at this designer's website and blog - she's self-published a book on using resin in jewellery and uses both epoxy and polyester.
PennyDog Jewellery - Handmade jewellery by Kerry Wilkinson. She's also really helpful if you email questions!

Hi Daisychain

Thanks for your reply and the helpful link. Yes, I think you are onto something here. I managed to obtain the technical specification for a similar resin and right at the end it had a short paragraph on using resin with silicone moulds. The recommendation was that you heat the mould prior to pouring.

I tried this last night but the result was the same, sticky. So I will try again this evening and heat the mould even more (I am being VERY cautious in heating these moulds), I will probably also increase percentage the Part B again.

I like your idea of epoxy but want the ability to create clear pieces from time to time, so I need to figure this process out.

Thanks again, I am off to look at your link.

Regards
Des

Hi there.

I also use polyester resin a lot in my work and I'm afraid to say that tackiness is something that can't really be avoided, as it was really designed for bigger jobs like boat building with fibre glass etc, so the outter layer was designed to stay tacky for them to do.... well boaty things with.
though after a lot of testing over the years a couple of methods i have used help somewhat.

When item has had its right curing time (in a nice warm place) demould and put in an air tight container, i tend to use ice cream tub or something similar. I then wrap this up in a zip lock back or cling film. This stops any air getting to it which causes the outer tacky layer to cure. but wont be very smooth or shiney.

You can also get an epoxy spray on resin which can seal the layer (but only ever coat polyester with epoxy... not the other way round) from Cindy (Lovely lady) at Resin Obsession (she has an eBay shop and a website)

The other method is scoring/scrapping the tacky layer off after soaking in warm soapy water (another anti oxygen method) then gradually working though the grades of wet and dry sandpaper ( usually tarting with 180 some times going as high as 1000)

I hope this all helps. I know it would have helped me a couple of years ago, Im more than happy to share the methods i have developed over the years so don't hesitate to ask.... if you think this has been useful that is xx