What is stucco?

What is stucco made of?

It is sand and water bound with lime, cement or both. The NPS brief traces the change from lime to portland cement around 1900, and in Minnesota the state code lists five cement types allowed for exterior plaster, including plastic (stucco) cement under ASTM C1328: “Before the mid-to-late nineteenth century, stucco consisted primarily of hydrated or slaked lime, water and sand, with straw or animal hair included as a binder.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29. “After about 1900, most stucco was composed primarily of portland cement, mixed with some lime.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29. In Minnesota, “Cement materials shall be in accordance with one of the following: 1. Masonry cement conforming to ASTM C91 Type M, S, or N. 2. Portland cement conforming to ASTM C150 Type I, II, or III. 3. Blended hydraulic cement conforming to ASTM C595 Type IP, IS (<70), IL, or IT (S < 70). 4. Hydraulic cement conforming to ASTM C1157 Type GU, HE, MS, HS, or MH. 5. Plastic (stucco) cement conforming to ASTM C1328.” Source: Minnesota Office of the Revisor of Statutes, read 2026-10-29.

How does the National Park Service define stucco?

Stucco is the plaster coat on the outside walls of a house. The National Park Service's guide to stucco, Preservation Brief 22, says the words plaster and stucco have long been used for the same thing, and that it is usually put on in three coats: “Historically, the term "plaster" has often been interchangeable with "stucco"; the term is still favored by many, particularly when referring to the traditional lime-based coating.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29. “Stucco is primarily used on residential buildings and relatively small-scale commercial structures.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29. “Like interior wall plaster, stucco has traditionally been applied as a multiple-layer process, sometimes consisting of two coats, but more commonly as three.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29.

How thick is stucco?

The NPS brief gives coat-by-coat figures: a first coat of about 1/4 to 3/8 inch, a second coat of about the same, with the two together generally not over about 5/8 inch, then a finish coat of about 1/4 inch. Minnesota's code sets the number of coats by what the stucco goes over: “After thoroughly dampening the masonry or wood lath, the first, scratch coat should be applied to the masonry substrate, or wood or metal lath, in a thickness that corresponds to the original if extant, or generally about 1/4" to 3/8".” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29. “The second coat should be about the same thickness as the first, and the total thickness of the first two coats should generally not exceed about 5/8".” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29. “The finish coat, about 1/4" thick, is applied after the previous coat has initially set.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29. In Minnesota, “Plastering with portland cement plaster shall be not less than three coats when applied over metal lath or wire lath and shall be not less than two coats when applied over masonry, concrete, pressure-preservative treated wood, or decay-resistant wood as specified in Section R317.1 or gypsum backing.” Source: Minnesota Office of the Revisor of Statutes, read 2026-10-29.

Is stucco waterproof?

No. The NPS brief calls stucco a protective coating that is still easily damaged by water, and the Minnesota code does not rely on it to keep water out: over wood-based sheathing it requires two layers of water-resistive barrier behind the plaster: “Like most historic building materials, stucco is at the mercy of the elements, and even though it is a protective coating, it is particularly susceptible to water damage.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29. In Minnesota, “Water-resistive barriers shall be installed as required in Section R703.2 and, where applied over wood-based sheathing, shall include two layers of a water-resistive vapor-permeable barrier.” Source: Minnesota Office of the Revisor of Statutes, read 2026-10-29.

Is stucco fire resistant?

Stucco is a cement-based coating, and FEMA's wildfire mitigation sheet WF-2 names it as ignition-resistant siding next to rock wall and cement board. That is a listing of materials, not a rating for any one wall, and the NPS brief describes only some fire protection: “Siding – Encasing building with ignition resistant siding such as rock wall, stucco or cement board.” Source: FEMA (copy hosted by the California Governor's Office of Emergency Services), read 2026-10-29. “The use of noncombustible or fire-resistant materials for exterior components and the creation of a defensible space can increase a building’s chance of surviving.” Source: FEMA (copy hosted by the California Governor's Office of Emergency Services), read 2026-10-29. “As a weatherrepellent coating, stucco protected the building from wind and rain penetration, and also offered a certain amount of fire protection.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29.

Can stucco be painted?

Yes. The NPS brief says many stucco buildings have been painted over the years, and it gives limits on paint type: latex can go on slightly damp walls but not chalky ones, and oil-based paint needs dry walls: “Many stucco buildings have been painted over the years and will require repainting after the stucco repairs have been made.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29. “Latex paint, for example, may be applied to slightly damp walls or where there is an excess of moisture, but latex paint will not stick to chalky or powdery areas.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29.

How long does stucco take to cure?

The NPS brief gives three time spans: 24 to 72 hours for each coat to dry before the next, 48 to 72 hours of keeping new work damp in hot weather, and up to a year before new stucco takes oil-based paint: “It usually takes 24-72 hours, and longer in cold weather, for each coat to dry before the next coat can be applied.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29. “It is also a good idea in hot weather to keep the newly stuccoed area damp, at approximately 90 per cent humidity, for a period of 48 to 72 hours.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29. “Oil-based, or alkyd paints must be applied only to dry walls; new stucco must cure up to a year before it can be painted with oil-based paint.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29.

Does stucco crack?

It can. The NPS brief names two causes, mixing hard portland cement stucco with softer lime stucco and letting fresh stucco dry too fast, and it says small hairline cracks are usually not serious: “The differing expansion and contraction rates of lime stucco and portland cement stucco will normally cause the stucco to crack.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29. “Small hairline cracks usually are not serious and may be sealed with a thin slurry coat consisting of the finish coat ingredients, or even with a coat of paint or whitewash.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29. “To prevent cracking, it is imperative that stucco not dry too fast.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29.

How long does stucco last?

The NPS brief gives no number of years. It says historic stucco is not a permanent material and that its life depends on regular maintenance, even though some stucco houses have lasted more than a century: “Although A. J. Downing alluded to stuccoed houses in Pennsylvania that had survived for over a century in relatively good condition, historic stucco is inherently not a particularly permanent or long-lasting building material.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29. “Regular maintenance is required to keep it in good condition.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29.

What is stucco lath?

Lath is the backing the stucco grips on a wood-framed wall; over brick, stone or concrete it is not needed. The NPS brief traces the move from wood lath to expanded metal lath, and in Minnesota the code sets corrosion-resistant lath fixed with nails or staples no more than 6 inches apart: “But on wood structures, stucco, like its interior counterpart plaster, must be applied over lath in order to obtain an adequate key to hold the stucco.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29. “Stucco is applied directly, without lath, to masonry substrates such as brick, stone, concrete or hollow tile (Fig. 7).” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29. “Wood lath was gradually superseded by expanded metal lath introduced in the late-nineteenth and early-twentieth century.” Source: National Park Service, U.S. Department of the Interior, read 2026-10-29. In Minnesota, “All lath and lath attachments shall be of corrosion-resistant materials.” Source: Minnesota Office of the Revisor of Statutes, read 2026-10-29. In Minnesota, “Expanded metal or woven wire lath shall be attached with 11 gage nails having a 7/16-inch (11.1 mm) head or 16 gage staples, spaced at no more than 6 inches (152 mm) or as otherwise approved.” Source: Minnesota Office of the Revisor of Statutes, read 2026-10-29.

What is a stucco weep screed?

A weep screed is the metal or plastic strip at the bottom edge of a stucco wall that lets trapped water drain out. In Minnesota the code requires one at or below the foundation plate line, at least 4 inches above soil or 2 inches above paving: In Minnesota, “A minimum 0.019-inch (0.5 mm) (No. 26 galvanized sheet gage), corrosion-resistant weep screed or plastic weep screed, with a minimum vertical attachment flange of 3-1/2 inches (89 mm) shall be provided at or below the foundation plate line on exterior stud walls in accordance with ASTM C 1063.” Source: Minnesota Office of the Revisor of Statutes, read 2026-10-29. In Minnesota, “The weep screed shall be placed a minimum of 4 inches (102 mm) above the earth or 2 inches (51 mm) above paved areas and shall be of a type that will allow trapped water to drain to the exterior of the building.” Source: Minnesota Office of the Revisor of Statutes, read 2026-10-29.

Sources

• Preservation Brief 22: The Preservation and Repair of Historic Stucco — National Park Service, U.S. Department of the Interior; published October 1990; read 2026-10-29.
• Minnesota Rules part 1309.0703: Section R703, Exterior covering (R703.7 Exterior plaster) — Minnesota Office of the Revisor of Statutes; published Current rule as published on 2026-10-29; read 2026-10-29.
• FEMA Mitigation Funding Opportunity WF-2: Ignition Resistant Construction - Residential — FEMA (copy hosted by the California Governor's Office of Emergency Services); published Undated FEMA sheet WF-2 (copy read 2026-10-29); read 2026-10-29.