Diagnose this casting resin issue

[SmilingOtter]

OK, here's the deal: I'm using Alumilite "Slow Set 7" pouring into an open silicone mold of some pilot wings I'm going to be giving away at 501st troops.

It pours fine, but as it cures, it expands, so it ends up considerably thicker than I wanted, and the back side of the pin isn't nearly as smooth as I'd like, so I have to sand it down to be usable.

I've seen that humidity could be the issue, does that sound right? I'm in Georgia, so that will always be an issue, unfortunately...

I don't have any sort of vacuum or pressurizing setup, and don't really want to invest in anything too pricey for an otherwise.



Thanks in advance.

 

[TazMan2000]

If you're talking about the curing "bump", I may have a solution. When I cast an open mould and need the open side flat, I place a rectangular piece of RTV over top of the poured resin. Its almost like a two piece mould without the registration keys. If you roll it on, rather than place the rectangular piece of RTV flat, you will avoid bubbles. You could also wipe a little resin on the flat piece of RTV for the same effect. Put something with a bit of weight to in on top of the mould to squish out the extra resin but not so heavy as it will deform the mould. Obviously it does get messy so ensure you cover your work area.

TazMan2000

 

[SmilingOtter]

Ooh, hadn't thought of that. And it won't stick to the silicone (much.) I'll try that, thanks!