Woodland Scenics Plaster? How do you *correctly* use it?

While I haven't used this particular product, it sounds like you got a bad box. There shouldn't be any lumps, bumps, tumors, kidney stones or anything else other than powder in there.

Just go to the local hardware store and get some Plaster of Paris. It's got to be much cheaper than the WS product......and without the lumps!

Here is a technique I use with plaster to produce a fine-grain surface texture. Shape the plaster to your desired form and while the plaster is still wet, take a tea strainer or a piece of window screen and sift dry plaster onto the wet plaster. It will stick immediately to form a fine, grainy texture. Let dry and harden, then paint with dilute tempera paint, allowing the colors to blend while wet.

I  was kind of thinking that, when I opened it, but I though the water would dissolve it somehow. Oh well, I'll use your advice and your technique.  

You got a bad carton - at some point it got wet or damp ... or it could have just been sitting on the shelf at the hobby shop for 10 years, which seems to be the case with some of the more obscure supplies at my local hobby shop. If you have a large strainer, I would try straining the mix through that, and then using your thumb to press the chunks and bits through the strainer mesh to break them up.

Well, nobody goes to THAT lhs for these supplies, they go to the model railroad one. I've never seen any dip in the amount ouf stock of the plaster in the 3 years I've gone there. Always the same 4 cartons sit there for 3 years. Probably longer....