STUCCO
Modern
stucco
Modern Stucco usually consists of 1 layer of wire lath and
2 layers of Portland cement-based plaster. This is due to
its rapid strength development and durability. However,
cement's crystalline structure cannot accommodate
significant movements in the building structure (as lime
does) and is thus prone to cracking. This is why an
additional acrylic finish on top is often applied. It adds
flexibility for surface movements and is waterproof.
First a wire mesh is attached to vapor permeable,
water-resistant "tar" paper if stucco is being applied to a
wood framed structure or light-gauge steel frame structure.
The paper protects the sheathing and interior of the wall
from outside moisture intrusion without trapping moisture
vapor in the wall. A wide variety of accessories such as
weep screeds, control and expansion joints, corner-aids and
architectural reveals are sometimes also incorporated into
the lath. Wire lath is used to give the plaster something
to attach to and may be expanded-metal lath, woven-wire
lath, or welded-wire lath. In Europe, wire lathing with
fired clay an integral "brick-mesh" is used in many
applications instead of expanded metal lathing.
The first layer of plaster is called a "scratch coat",
consisting of plastic cement and sand. A brush is used to
scratch the surface horizontally or in a criss cross
pattern to provide a key for the second layer.
The next layer is called the "brown coat" or leveling coat.
It also consists of sand, cement and lime. It is leveled
with tools called "Darbys", "Rods" and "Federege" scraped
smooth, and floated to provide a nice even surface onto
which to apply the finish coat. It is then allowed to dry
(cure) for 7-10 days minimum to allow "checking"
(shrinkage)and cracking to take place. Sometimes the dry
surface is sprayed with water for one or more days to speed
up the curing process.
The exterior stucco layer is the final layer and is
referred to as the "finish coat". There are 2 different
recommended types of finish coats:
1. Color Coat is a colored sand, cement and lime mixed
finish and is typically 3 mm (1/8") thick. A base coat of
stucco is applied over the 2nd coat of cement (brown coat).
This then can be floated with water for a sandy finish or
later textured over with a trowel to create various styles
of troweled finishes. Pre-mixed stucco is what's mostly
used and comes in coarse graded sand and finer graded sand
for creating a very smooth troweled finish. It is made in a
variety of colors.
2. Acrylic Finish is an acrylic based finish from 1,0 mm to
4,0 mm thick. It can be applied in many ways, and is the
most recommend finish for long lasting quality. It also can
be ordered in any color.
3. Hard Coating is another method of adding a finish to the
stucco wall, although no longer recommend. In the 60's and
70's people added a variety of materials like glass chunks,
stones or marble (calcium carbonate finished with crushed
natural marble (Marmalrino)) into the wet stucco wall. This
kind of finish coat is very heavy and inflexible, and also
hard to repair.
information courtesy of Wikipedia