Join Date: Nov 2007
Location: Tacoma, WA "America's Most Wired City"
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Drywall compound isn't intended for the use you have in mind. It doesn't set up very hard (so it sands easily), and will crack if you apply it in thick layers because the outside dries (and therefore shrinks) faster than the inside. That's because it dries by evaporation of the water the powder is mixed with.
For what you want to do, you're better off using plaster. It's available premixed in bags (just add water, the directions are on the bag). It is formulated and intended for use as a wall surface, as opposed to drywall compound, which is intended only to bridge the small spaces between sheets and to repair small surface defects. Plaster sets by a chemical reaction between the powdered contents and the water it's mixed with (like concrete), so cracking due to differential drying rates between surface and interior layers isn't as much of a problem. Plaster mixes come formulated for various drying times, and with the sand already mixed in if you want a sand texture.
Whatever you use, you do need to use some kind of lath. Chicken wire will work, but expanded-metal lath, which you can buy at a plastering supply house, has smaller openings and thus creates a much stronger mechanical bond (the plaster oozes through the openings and dries behind the lath, forming "keys" that hold the plaster layer in place). If you don't use lath your surface coating will not stay on the wall for long.
There's no need to cover the wood with drywall first, but if you do, you need to use greenboard, not ordinary drywall. Greenboard is intended to have a skim coat of plaster applied over it, whereas ordinary drywall isn't intended to have so much water applied to its surface. The drywall's paper surface will absorb all that water and pass it through to the gypsum layer, causing it to disintegrate.