You may apply stucco directly over these rigid, solid surfaces, but only if the surface is roughly textured and absorbent. If the wall does not absorb a sprinkle of water, or if there's obvious surface contamination, wash the surface thoroughly. If the wall is coated in paint or sealer, or if it's too smooth to support stucco, try one of the following treatments:Acid etching
Sandblasting
Bush hammer or roughing machine (for unpainted, smooth surfaces)Applying a bonding agent, referring to specific product instructions. Do not use over water-soluble paint.If there is any doubt that the wall can support the stucco, follow the instructions in the stud wall section above, attaching metal lath and plastering over it.
 Wet the wall right before you apply the first coat of plaster, preferably with a fog spray. This improves the suction bond and reduces the amount of water the wall absorbs from the plaster, preventing premature drying. The surface should be damp, but not soaked.Delay the job if the next week of weather involves freezing temperature, hot weather (above 90ºF / 32ºC), or high wind. These conditions will interfere with the curing process.
 This coat should be 1 part cement material (including lime) and 2¼ to 4 parts sand.Plastic cement, which has been pre-mixed with lime, is usually the easiest to mix and work with. Combine this with plaster sand from a dry material yard.Only add enough water to allow you to trowel the plaster, or it may sag or fail to stick to the wall.
 Trowel on a layer ¼ inch (6.4 mm) thick.Score this with shallow, horizontal lines using a notched trowel, keeping the tool perpendicular to the wall.These grooves will help the next coat bond onto the surface.


Acid-etched surfaces (among others) may not be quite rough enough for a strong bond with this method. Instead, dash on the scratch coat using a cement gun, or by whipping it on with a fiber brush or whisk broom. This forces out air to create a stronger bond.Some builders combine the scratch coat and brown coat into one base coat. If you choose to do this, plan on a total stucco thickness of about ⅜" (9.5 mm) for cast concrete, and ½" (12.7 mm) for unit masonry.Allow about ¼" (6.4 mm) of this thickness for the finish coat., With modern cement on a rigid surface, there is no need to wait for the scratch coat to cure completely. For a stronger bond, trowel on the second, "brown" coat as soon as the scratch coat is rigid enough to resist cracking, usually after four or five hours.Rod and float this surface until it is level and ¼" (6.4 mm) thick.The brown coat mix should contain 1 part cement materials and 3 to 5 parts sand.It may help to compact this layer with a shingle float.
 Over the next 48 hours, it is critical to keep the stucco moist. If the relative humidity of the air is below 70%, you will need to mist or fog the surface once or twice a day.Wait at least seven days for the brown coat to cure, wetting periodically if it begins to dry prematurely. Some organizations recommend 10 or even up to 21 days of drying for even more crack resistance.In extremely hot or windy conditions, put up a windbreak and sun shade. You may even need to cover the moistened surface with polyethylene.
 The decorative finish coat contains 1 part cement materials and 1½ to 3 parts sand.Optionally, it may include pigment as well to add color. Trowel and float this on in a thin layer, about ⅛" (3 mm) thick.Allow it to cure completely before painting (if desired), following the same moist curing instructions above if the weather is hot.
Prepare the wall's surface.
Wet the surface.
Mix the scratch coat.
Apply and score the scratch coat.
Apply the brown coat after a few hours.
Keep the brown coat moist while it cures.
Put on the finish coat.
{"src": "wikihow-all_test", "title": "How to Stucco a House2"}