Hi Genny,
My soap base is from a place called The Soap Kitchen (in the UK). The base is made by a company called 'Stephenson' and it's called, Melt & Pour Soap Base (Crystal) Eco Palm Free, Clear.
The ingredients are: Glycerine: Aqua: Sodium Stearate*: Sodium Olivate: Sorbitol: Sodium Cocoate: Decyl Glucoside**: Sodium Chloride: Citric Acid.
*= Derived from Rapeseed Oil, **= Coconut Derived.
Thinking about it sometimes I add a little extra glycerine, for example enough so I can mix in some seaweed or clay into the base, but try to be careful not to use anymore than needed, I wonder if this makes a difference? (I think you made this suggestion to me and it works well).
I am in England and it's not that humid here at the moment, though we've had the occasional hot day, but it would be nothing compared to what you'd have in the states! The hottest day we've had all year was 30.4C (86.7F), but really that was a freak occurrence! Today is 19°C (62.2F), pretty normal-ish really.
I think some of my problems stem from keeping the soaps in a the garage (we had a stage where it was cold and rainy) and then putting them in a hot car for a few days, after that is when I noticed how many of them were sweating badly. The people who I buy the base from said that this would be part of the problem. I have also noticed that the ones that have sweated far worse are the citrus ones more than than the other ones (eg. peppermint or eucalyptus).
I recently found a bunch of soaps that haven't sweated at all (made back in May) though they have shrunk!. They were some of the first ones I made and I hadn't used any extra glycerine in them or kept them in extreme temps. So I know the soaps don't always sweat so bad! It's just hard to pin point exactly what has caused it (probably both things...maybe?!)
Lisa x