Mold maintenance?

[Dr Mathias]

Hello,
I'm happy to report that I made my first split molds using the fine guides on this site and have been toiling away making casts.

I'm using MoldMax 20, vacuum degassed then poured.
I settled on SmoothCast 305. 300 was just too fast setting, I was having trouble with airpockets.
Pressure cast at 50-60 psi, using a Harbour Freight pot (I know, I know... I bought it before finding this resource!). I plan to upgrade to something legit, and soon.

I am using talc (baby powder, mainly because I already had it) to help the resin flow through the mold.

What I am finding is that after a number of casts, the talc builds up a bit at the bottom of the split. Very thin layers of resin are also 'sticking' in flash areas between the split. It is easily removed with a fingernail or stiff brush.

Castings are fine, no unacceptable mold split lines or anything, but it raises the question of cleaning out the mold. Eventually I can see the talc and flash causing excessive flash.

Should the mold be washed out occasionally?
Should I be using a release agent?
Is it normal to have some periodic buildup?
I haven't tried casting without talc yet- how necessary do you feel it is?

Thanks in advance!

[mangozac]

Great to hear you're having some success already!

Smooth Cast 300 is indeed far too quick setting and I wouldn't recommend it to a beginner. 305 is a good product and I would use it if weren't so expensive here...

When casting using pressure only talc definitely seems to help prevent bubbles from sticking to detailed surface areas. In other experiments I did though I concluded that it does nothing to help mould lifespan - wax or lecithin based release sprays are best for that.

Both talc and release sprays will build up like you have experienced. I keep a microfibre cloth at my casting bench and just wipe off the residue when I notice that flash has started to form.

[Dr Mathias]

Thanks for the reply, interesting info.

Can a spray mold release be combined with talc?
If so, in what order should I proceed and do I need to wait for the release to 'dry' ?

I have Mann Ease Release 200.

[mangozac]

I've not tried but I don't think so. Not easily anyway. The mould release will leave an ever so slightly gooey film which the talc will stick so and prevent the talc from performing its function.

[Dr Mathias]

Thanks again for the advice. I pretty much assumed the mold release and talc would not be a great combination. I may try it with an extra bit of resin on a old mold just for kicks.

[factor40]

I responded to,your message but I thought I'd post this here as well. If can apply a vaccuum before going to pressure, you might be able to skip the talc altogether. That might help prolong the usefulness of your molds. Another thing I do is store my molds in plastic shoeboxes, I beleieve not being exposed to air as much helps prolong them as well.

[rattrap]

I was advised by a very experienced resin caster that it is better to let the moulds breath and allow them to be exposed! I had always sealed them in plastic boxes before.

Would be interesting to hear what everyone else does.

[mangozac]

I've never heard that it's good to let them breathe and I know of a few people who store them in sealed containers or zip lock bags. Most of my moulds are production moulds so their lifespan isn't long enough to worry about time based degredation. So I don't do anything special.