I saw this post on lining a mould using liquid Latex. As I had some in stock I thought I would give it a try.
I have to say it takes a LONG time to do. About 3 days in total. I waited for it to dry in between coats but then had to go off to make a delivery or make soap. I am sure it would probably only take a day if you were dedicated but I do tend to multi task (not always a good thing).
I used a product called Dala Casting rubber that you paint on. It is available in most craft stores. Use a large fine bristled brush and paint on a thin layer. It looks white when you first paint it on then dries to a yellowish colour.
I painted 4 coats but I think I will do more next time. It is quite thin but totally useable.
Once dry, I peeled from the wood and then clipped it back on to keep it upright. The sides are so thin they just collapse back on themselves.
Peeling the mould off the soap is SUPER easy. The only problem I did have was that the bottom pitted into the soap - right picture
Here is the finished soap. NICE