Estimating stucco before you order
Stucco is a cement plaster applied to exterior walls, usually in several coats over metal lath or masonry. It is sold dry in bags, so the estimate comes down to the weight of material needed to cover your wall area at your chosen thickness, plus a margin for waste.
The calculation
- Area to cover = wall area − doors and windows.
- Dry material = area × thickness × material rate × (1 + waste).
- Bags = dry material ÷ bag weight, rounded up.
The material rate is the weight of dry mix needed to cover one square foot one inch thick. Most premixed stucco is about 8 to 11 lb per square foot per inch. An 80 lb bag of base coat that yields about 0.75 cubic feet works out to roughly 8.9 lb; check the coverage printed on your bag and adjust.
Worked example
A wall of 500 sq ft has 60 sq ft of windows and doors, leaving 440 sq ft. A traditional three-coat system is 7/8 inch thick in total. With a material rate of 8.9 lb and a 10% waste allowance:
- Dry material: 440 × 0.875 × 8.9 × 1.10 = 3,769 lb.
- 80 lb bags: 3,769 ÷ 80 = 47.1, so 48 bags.
- Coverage: about 9.3 sq ft per bag at full thickness.
- At $15 a bag, the material costs $720.
Typical thicknesses
| System | Thickness |
|---|---|
| Scratch coat | 3/8 inch |
| Brown coat | 3/8 inch |
| Finish coat | 1/8 inch |
| Three-coat stucco, total | 7/8 inch |
| One-coat stucco over foam | 3/8 to 1/2 inch |
If you estimate coats separately, use the thickness and material rate of each product, since base coats and finish coats yield differently.
Tips for a good job
- Order a little extra from the same production batch: color can vary between batches of finish coat.
- Do not apply below 40 °F or when frost is expected within 24 hours.
- Keep each coat damp for 48 hours in hot or windy weather so it cures rather than dries.
- Let the brown coat cure, often 7 days, before the finish coat, unless the manufacturer allows a shorter wait.
- Building codes, such as the International Residential Code, set lath, weather barrier and weep screed requirements. Check with your local building department.