Stir the Mud

A 50-pound bag of American Clay’s Loma plaster (also sold at Ecohaus) yields one coat per 200 square feet, so measure your space to determine how many bags you’ll need. Pigments, which are sold separately, are available in a palette of 43 colors, from clean blues and grays to earthy reds and golds. You can also special order a custom hue or even enhance the pigment’s depth and luster by adding mica chips, shredded straw, or recycled colored glass.

For the best results, mix your plaster 4 to 8 hours prior to application. Before you get started, pick up a particulate mask (inhaling clay dust is hazardous to your lungs), rent a heavy-duty low-speed ½-inch drill ($12 per day at Home Depot, www.homedepot.com), buy an attachable mixing paddle and a 5-gallon bucket, and lug it all into the garage to avoid any catastrophic spills. Follow the directions on the Loma package for blending the plaster and the pigment (for more detailed instructions and techniques, visit American Clay’s website at www.americanclay.com). Keep the drill on a low speed to avoid creating air pockets. When it’s ready, the plaster should have the consistency of a thick milkshake, with the pigment spread throughout. (If the plaster dries out between mixing and applying, just add water to return it to the right consistency.)

Apply the Plaster

The technique here is all in the position of your trowel. Hold it at a 30-degree angle to the wall and sweep upward, reducing the trowel’s angle slightly as you go but maintaining consistent pressure.

The Hawk and Trowel

No, it’s not a pub in London. These are the traditional plastering tools you’ll need to spread your two coats of clay. The hawk looks like a tray resting on a handle, and the best trowel for this project will be a rectangular one made of rigid steel.

Hold the hawk in your nondominant hand, keeping the tray level, and pour about 1 cup of plaster onto it. Scoop half of that onto the trowel’s flat surface. Starting at the floor, hold the trowel at a 30-degree angle to the wall, with the bottom edge against the wall, and apply pressure while sweeping upward, keeping your trowel angled. Unless you’ve plastered before, your instinct will be to immediately flatten the trowel against the wall—this is an excellent way to create thick, clumpy layers, so resist it. Another challenge for first-timers, says Adams, is to avoid putting the plaster on too thick, which causes it to crack as it dries—so it’s important to watch your trowel’s angle and maintain consistent pressure until you have a smooth, thin coat (about 1/16 inch thick is best for the base coat). If ridges, clumps, or rough spots remain (and they likely will), smooth them by scraping the trowel clean against the hawk and using the trowel’s edge to sweep horizontally across the plaster you just applied.