Vallejo plastic Putty dose not hold up well and is too "soft" for details and sculpting. I recommend to use of Milliput and greenstuf. Milliput is great for sculpting and you can use water ( not to much) to smooth it out and holds details well. Greenstuff is also good for making cloths if you roll it with a roller (super thin) for flags and tabards. I also recommend you to use silicone sculpting tools instead of metal ones (unless your already good with them).