Constructing foundations and walls with concrete block is an easier
and usually less expensive alternative than poured concrete or stone
construction, but the result is not very attractive. Stucco, a
custom-mixed or factory-prepared cement plaster, provides an
inexpensive, durable, attractive, and low-maintenance finish on
interior or exterior foundation and garden walls in any climate.
Generally you can use a time-tested Portland cement plaster (1 part
Portland cement, 1 part lime, and 4 parts fine sand) for a base
coat. While lime is not necessary, it extends the working time of
the stucco - a plus for the inexperienced worker. For more uniform
batch-to-batch consistency and color, it's safer to choose a
factory-prepared stucco for the second, finish coat.
Apply stucco in mild (50- to 70-deg. F.) weather. Application can be
as simple or complex as your skills and experience allow; and the
textures that you can achieve are limited only by your imagination.
The basic steps are outlined below. Local conditions, sand
qualities, and specifics of your project may call for special mixes
or additives. White cement and white sand, for example, may be the
best choices for white or light-colored stucco. Bonding additives
may be required for certain non-absorptive surfaces. Your masonry
dealer is best equipped to advise you about the right mix to use for
your particular application.
Tools and Materials Needed
Mortar mixer (rental item shown)
Power washer (rental item)
Wood lath and masonry nails
Hawk (board with handle for loading cement)
Garden hose and nozzle
Common mason's trowel
Type I Portland cement
Pointed mason's trowel
Long metal or wood straightedge
Clean fine sand
Wood float (wood block with handle)
1. Inspect and Prepare the Surface
The block wall must be sound and true, and significant holes or
cracks should be repaired. The surface must also be free of dirt,
mold, efflorescence, paint, or other surface contaminants that might
interfere with bonding. Typically, power-washing is all that is
required for older untreated walls, although in some cases
sandblasting is necessary.
2. Install Screed
Attach temporary strips of 3/8-in thick wood lath horizontally to
the top and bottom (and, on a tall wall, the middle) of the wall,
using masonry nails. These screeds will guide the straightedge
(called a rod) that is used to level the surface in Step 7.
3. Obtain Materials
One cubic foot of stucco will cover about 17 square feet of wall for
the base coat. Expected coverage for factory-prepared finish stucco
is stated on the label. You need about 1 cubic foot of damp sand and
1/4 to 1/3 bag of cement and the same amount of lime to make a cubic
foot of plaster.
4. Dampen the Wall
Stucco is best applied over a damp wall, so mist (not soak) the
surface with a garden hose and nozzle just prior to application.
Cement and lime are caustic. Before you begin mixing, protect your
hands with heavy work gloves and your eyes with goggles.
5. Mix the Base-coat Plaster
For large jobs you'll want to rent a power mortar mixer. First add
about 2/3 of the water and start the mixer. In succession add about
half the sand, the cement, the lime, and the balance of the sand.
Mix for a few minutes, adding the remaining water as needed to
achieve a uniform batch. If you mix with a hoe in a wheelbarrow, mix
the dry ingredients first and mix in half the water immediately and
then add the rest as needed. Although dry ingredients can be
measured out in buckets, generally you just count shovelsful as you
load the mixer or wheelbarrow.
Weigh shovelsful of lime and cement separately so you can calculate
approximate water needs for your mix. Water, which weighs about 7.8
pounds per gallon, should equal approximately half the weight of the
cementitious material (cement and lime) in the mix. Experiment with
a couple small batches first to determine the amount of water
required. The mix should have the consistency of pudding or soft
butter. You can retemper the mix (add water when the mix has become
too stiff) up to 30 minutes after the initial mixing.
Apply the Base Coat
Load some stucco on a hawk and then onto your trowel. Initially hold
the loaded trowel at a 45-degree angle against the wall, and reduce
it slowly to 30 degrees as you apply the stucco with a sweeping
motion. Apply sufficient pressure to force the stucco into the rough
wall surface. On vertical surfaces you'll probably find it easiest
to work from the bottom up. The base coat should be about 3/8-in.
thick over the entire area. Avoid excessive troweling, which can
cause bonding problems.Load some stucco on a hawk and then onto your
trowel. Initially hold the loaded trowel at a 45-degree angle
against the wall, and reduce it slowly to 30 degrees as you apply
the stucco with a sweeping motion. Apply sufficient pressure to
force the stucco into the rough wall surface. On vertical surfaces
you'll probably find it easiest to work from the bottom up. The base
coat should be about 3/8-in. thick over the entire area. Avoid
excessive troweling, which can cause bonding problems.
7. Level the Plane
After just a few minutes use a straightedge (metal or wood)
to level the surface to a uniform 3/8-in. thickness. Place
the ends of the straightedge on wood or metal screeds (see
step 2) and, using an up and down motion, slowly draw the
straightedge across the wall to remove excess material. Fill
any depressions and repeat leveling.
8. Remove Screeds
Remove the wood screeds with a nail puller and hammer, disturbing
the stucco as little as possible.
9. Float the Surface
After the surface sheen has disappeared but before the stucco has
hardened too much to be worked, go over the entire surface with a
wooden or foam mason's float in a swirling motion. This consolidates
the stucco and reduces the amount of shrinkage and cracking that
occurs as the base coat cures.
10. Mix and Apply Finish Coat
Mix and apply the finish coat the next day. This coat is typically
only 1/8 to 1/4 inch thick so screeds are not needed. The procedure
is otherwise similar to the above. There are differences from
product to product, however, so follow the manufacturer's
11. Texture the Surface
Dozens of textures are possible. Among the simplest is a somewhat
rough but uniform surface achieved by tooling the finish coat with a
sponge float or brush. In some cases an additional texture coat of
finish material is applied over the initial finish coat and tooled
with a trowel or other tool.