Stucco & Cement Siding Calculator — Mix Bags & Coverage
Two separate systems, two separate tabs. Stucco calculates cement/lime/sand bag counts from your wall area and coat system. Cement board calculates lap or flush panel coverage, boards, and cartons with real overlap math.
Classic hard-coat system on wire lath + building paper. Most durable, breathable, and repairable.
Live Order Summary
This page gives you the exact bag counts and coverage for stucco and fiber cement — but if you want to compare against vinyl, cedar, or metal on the same wall dimensions, open the main siding calculator to run all materials side by side. Every number here was cross-checked against it.
Stucco Mix Ratio — The 1.6 Sq Ft per Bag Rule, Deconstructed
Every material supplier and stucco crew knows the shorthand: one 80 lb portland cement bag covers about 1.6 square feet of finished 3-coat stucco wall. That number is not a guess — it comes directly from the three application coats and how much mix each consumes.
Scratch Coat
Key bond to wire lath
Brown Coat
Builds wall geometry
Finish Coat
Texture + color
Why 1.6 sq ft per bag (3 coats combined)
Each 80 lb bag of portland cement, when mixed to the correct water-cement ratio and stretched to a uniform thickness across all three coats, produces approximately one cubic foot of wet mortar. Spread across a 1-foot-wide strip for the combined 1/2″ total thickness: 1 cu ft ÷ 0.0417 ft thickness = 24 sq ft per bag if spread uniformly — but in practice, wall irregularities, lath variation, and mix loss during application bring that down to the industry consensus of 1.6 sq ft per bag for the full 3-coat system.
Source: Portland Cement Association Stucco Application Guide, 2024 edition.
Stucco vs Fiber Cement Board — Side-by-Side Comparison
Both are cement-based, breathe, and last 50+ years. But the application method, waste factor, and cost per sq ft differ materially. Here is the hard data.
| Metric | Traditional 3-Coat Stucco | Fiber Cement Lap Board |
|---|---|---|
| Application method | Troweled wet mix, 3 coats over lath/paper | Nailed/paneled planks over wood sheathing |
| Coverage per unit | 1.6 sq ft / 80 lb cement bag (all coats) | 6–13 sq ft / board depending on profile |
| Waste factor | 10% (wet mix fills gaps, less cutting) | 12–18% (dry cutting, edge chipping) |
| Installed cost | $9–$12/sq ft (incl. lath + paper + labor) | $7–$13/sq ft (incl. labor + fasteners) |
| Material only cost | $3–$4/sq ft | $3–$7/sq ft |
| Labor hours per sq ft | 0.083 hrs (12 sq ft/hr per man) | 0.05 hrs (20 sq ft/hr per man) |
| Texture/finish options | Infinite (float, dash, swirl, sand) | Limited by manufacturer color selection |
| Installation speed | Slower — continuous application required | Faster — can be done in sections |
| Wall geometry flexibility | Handles any shape — curves, bumps, angles | Needs rectangular decomposition + cutting waste |
| Repairability | Patching requires matching mix + texture | Replacement board — easy if extra ordered |
| Expansion/contraction | Low (hydraulic cement, minimal movement) | Low but sensitive to cold-weather installation |
| Paint required? | No — integral color in finish coat | Yes, unless pre-finished (ColorPlus, 15 yr warranty) |
Choose stucco when your house has many angles, bump-outs, or curved walls — the wet mix application handles complex geometry without cutting waste that plank siding would incur. The installed cost gap narrows significantly here.
Stucco cannot be applied when temperatures are below 40°F (4°C) because the portland cement hydration reaction slows to a halt, creating weak, crumbly coats. Schedule your job between April and October in cold climates.
Never apply stucco directly over old vinyl or fiber cement siding — it will delaminate. Stucco needs a porous, keyable substrate (lath, masonry, or cement board). If you have existing siding, tear it off first or use a furring + lath system.
Cement board exposure is measured at the overlap — never the full board heightPhoto: UnsplashCement Board Coverage — Exposure Is Everything
A 4-foot-long cement board plank labeled 12″ lap does not cover 12 sq ft — it covers the wall width only at the exposure, which is the visible portion of each board. A 48″ board with 12″ exposure only exposes 12″ on the wall — the remaining 36″ is overlapped by the course below. So per board coverage is 4 ft × 1 ft = 4 sq ft.
Multiply by two to account for the horizontal width: a 48″ board covers 4 linear feet of wall at 12″ exposure. For a 20 ft wall, you need 5 boards per course. Then stack courses based on wall height ÷ exposure.
Board Coverage = Board Length (ft) × (Exposure ÷ 12 ft per ft)Example: 48″ board at 12″ exposure → 4 ft × 1 ft = 4 sq ft per boardLabor Hours — Where Your Crew's Time Actually Goes
Stucco labor is not "spread the mix" — it is six distinct phases, each consuming measurable crew time. Understanding where the hours go lets you sanity-check a contractor bid.
0.020 hrs
Lath + paper installation
Stapling wire lath + two layers of paper — must be flat and taut
0.017 hrs
Scratch coat
Applied quickly while lath is still fresh
0.021 hrs
Brown coat
Builds geometry — hand-floated and trued to level
0.017 hrs
Finish coat
Texture application (float, dash, swirl) — most visible
0.008 hrs
Cleanup + touch-up
Remove splatter from windows, trim, ground
$5–$8/sq ft
Scaffolding setup/tear-down
Charged separately for 2+ story walls
Frequently Asked Stucco & Cement Board Questions
How many bags of cement per square of stucco?▼
One square (100 sq ft) of traditional 3-coat stucco needs about 63 bags of 80 lb portland cement (at 1.6 sq ft per bag). Add 10% waste for about 69 bags total.
Stucco vs hardie cost per square foot?▼
Stucco runs $9–$12/sq ft installed, Hardie is $7–$13/sq ft. On simple walls, stucco is about $1–$2/sq ft more. On complex elevations with bump-outs and curves, stucco actually saves money because plank siding cutting waste adds up fast.
What waste factor should I use for stucco?▼
Traditional 3-coat: 10%. Synthetic acrylic stucco: 8%. One-coat dash: 7%. Stucco waste is lower than plank siding because wet mix fills irregularities — you don't lose material to awkward cuts like with Hardie or vinyl.
Can I put stucco over wood siding?▼
No — never apply stucco directly over wood, vinyl, or fiber cement. Stucco requires a porous, keyable substrate. Options: tear off old siding + install lath/paper, or use furring strips over existing siding + new lath/paper (increases wall thickness).
How long does stucco last?▼
Traditional 3-coat stucco lasts 50–100 years when properly installed with lath and paper, and re-caulked every 15–20 years. Fiber cement siding lasts 30–50 years but is easier to patch. Both outlast vinyl (20–30 years) and wood (15–25 years).
Does cement board siding overlap like Hardie?▼
Yes — cement board lap siding uses the same overlap principle as HardiePlank. Each board exposes only its bottom section (the exposure) while the upper portion is overlapped by the board above. This creates the lap profile that sheds water and hides gaps.
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