Stucco is applied either by hand or machine to exterior and interior wall surfaces. It may be applied directly to a solid base such as masonry or concrete walls, or it can be applied to metal lath attached to frame construction, solid masonry, or concrete construction. Applied to metal lath, two coats form a 5/8-inch total thickness. A vapor-permeable, water-resistant building paper separates the plaster and lath from water-sensitive sheathing or framing. Cementitious stucco has high impact resistance and sheds water, but it also breathes, allowing water vapor to escape. It is a proven system that works in all climates.
Hardcoat stucco is instead installed over wood strips, known as lath, or over metal lath and does not use the foam underlayment. Hardcoat Stucco is usually 3/4″ to 1 inch thick and therefore will feel more solid (thicker) and give a solid thump if you tap on it.
EIFS Stucco Systems
Although often called "synthetic stucco", EIFS is not stucco. Traditional stucco is a centuries-old material which consists of aggregate, a binder, and water, and is a hard, dense, thick, non-insulating material. EIFS is a lightweight synthetic wall cladding that includes foam plastic insulation and thin synthetic coatings. There are also specialty stuccos that use synthetic materials but no insulation, and these are also not EIFS. A common example is what is called one-coat stucco, which is a thick, synthetic stucco applied in a single layer (traditional stucco is applied in 3 layers). There is also an EIFS-like product called a direct-applied finish system (or DAFS), which is essentially an EIFS but without the insulation, and has quite different characteristics.