A pack of Pro-Create modeling putty - http://www.kraftmark.biz/kraft.procreate.html
It comes in a practical plastic box with lid.
As you can see it comes in two wrapped bars - one is the resin and one the hardener.
So I gave it a try and took two even amounts of each and mixed them just like GS.
First impression?
GREAT!
It is softer than GS, so you may have to adjust your sculpting and modeling procedures, but is really easy to work with.
Here I started with the boots for the Ogryn.
The putty smoothens really nicely and is longer formable than GS, which is getting hard - not cured, just hard to form - rather quick.
Next I worked on a kind of powerfist or at least armored fist for the left hand.
it allready has some scars and scratches - I will still have to add rivets and stuff, but actually I'm pretty satisfied with this stage.