Written by Stucco Champions — Southern California’s Authority on Exterior Plastering.

The Skeleton of Stucco: A Comprehensive Guide to Selecting the Right Sand

When we mix stucco, cement is the glue, but sand is the skeleton. It makes up roughly 70% of the volume of your wall. The type, shape, and cleanliness of the sand you choose dictates the strength of the scratch coat and the beauty of the finish coat.

Using the wrong sand isn't just an aesthetic issue; it's a structural liability. In this guide, we break down the difference between "Washed Plaster Sand" and "Silica Sand," and why grabbing a bag of generic play sand from Home Depot is a mistake that could ruin your project.

1. The Gold Standard: Washed Plaster Sand (ASTM C144)

For the structural layers of stucco—the Scratch and Brown coats—you need aggregate that provides compressive strength.

• Why "Washed"? Sand dug straight from the ground contains silt, clay, and organic salts. These impurities kill the chemical bond of the cement. Washed sand has been sluiced to remove these fines.
• Angularity Matters: [Image of sand grain size comparison] Good plastering sand is "sharp" or angular. The jagged edges lock together like puzzle pieces when the cement cures. River sand is often too round (smooth), leading to weaker walls.

2. Sourcing: Bulk Yards vs. Bagged Goods

Where you buy your sand depends on the scope of your repair.

The Material Yard (Professional Route)

For re-stuccoing a whole house or a large addition, we go to dedicated Lath & Plaster yards (like Hub or Westside).
Pros: Consistent "pile" (color/texture match), bulk pricing, and adherence to ASTM C144 grading.
Cons: Requires a dump truck or trailer for delivery.

Bagged Sand (The DIY Route)

For small patches, bagged sand from a hardware store is convenient, but you must read the label.
Look For: "All-Purpose Sand" or "Concrete Sand" (Coarse/Medium).
Avoid: "Play Sand." (See warning below).

3. The Finish Coat: Silica vs. Plaster Sand

The rules change when we apply the final color coat. The size of the sand grain determines the texture of your home.

Coarse/Plaster Sand (16/20 Mesh)

Used for heavy textures like Spanish Lace or Machine Dash. The large grains create deep valleys and shadows, which is excellent for hiding imperfections in older walls.

Silica Sand (20/30 Mesh)

This is a manufactured, uniform sand used for Sand Finishes and Santa Barbara Smooth finishes.
The Benefit: Because the grains are identical in size, it allows for a tight, consistent trowel pass without the "drag marks" caused by larger rocks found in bulk plaster sand.

4. Matching Existing Texture

If you are patching a hole, you cannot just use whatever sand you have. You must match the "aggregate profile" of the existing wall.

• Rough Wall? Use All-Purpose/Concrete Sand.
• Smooth Wall? Use Fine Silica or specially graded "Velvet" sand.

Pro Tip: If you use fine sand on a rough wall, the patch will look like a smooth scar. If you use coarse sand on a smooth wall, it will look like a wart. The sand dictates the blend.

Conclusion: It’s Not Just "Dirt"

Selecting the right sand is the first step in a successful stucco project. For structural strength, stick to coarse, washed plaster sand. For refined finishes, upgrade to graded silica. At Stucco Champions, we filter our sand selection based on the specific architectural needs of your Southern California home.