Inexpensive plaster scraping tool.

[Jeff Longtin]

For anyone wanting to create a large piece of plaster, with a smooth surface , I offer this suggestion: a tool known as a "paint guide" is a wonderful tool for a potter.  (Essentially they're a scraper in a large format.)  I have two in my studio, one that is 12" wide and another that is 24" wide. They are cheap, under $10, and they are stainless steel. (So they don't rust.) They feature a stainless steel strip of metal set into a plastic handle. I use them to give my plaster molds a smooth surface on their topside. (Such that the mold doesn't wobble on the pouring table.) 

They would also come in handy if you're pouring a plaster wedging slab. Just run the tool across the surface of the setting plaster and you will have a nice smooth surface upon which to wedge your clay. 

[oldlady]

they can  smooth a large slab all at once so you can cut many things at the same time.   also known as a wallpaper smoother to remove bubbles as they form  under fresh wallpaper.

[Denice]

It is also great for using to trim wallpaper,  hold the smoother against the ceiling tightly and cut along the edge with your sharp wallpaper knife.   I have never thought of using it with plaster or clay,  I think I have one in storage if not they are inexpensive.  Another great thing you will find in a wallpaper store is  a  plastic and mesh strainer, fits on a 5 gal bucket and cost a few dollars.  They make it for painters to pour paint  through when they are mixing  (booking) several gallons of paint together.   Works great for your first pour when you make 5 gallons of glaze.   You never would  have guessed I owned a wallpaper and paint store years ago.   Denice