The Do's and Don'ts of Stucco

One of the oldest coverings for a home or dwelling is stucco coating. This lime, cement and sand mixture was used in different forms by the natives in American southwest, the Moors in North Africa and the Mediterranean dynasties well before the birth of Christ. This was because it went well over stone, brick and wood and sealed the structure from the wind and elements. Today it is one the main exteriors for homes in the hot, dry areas of the country.

Traditionally, stucco was composed of lime, sand and water but now portland cement is added. Adding lime allows the stucco to flexible when applying and also is a sealer against water. Other additives like glass fibers and acrylic strands strengthen mix and prevent it from cracking and it can be applied with a trowel or sprayed on.

The Stucco Process

Stuccoing requires to proper tools and, if you are going high, a scaffolding. Working from a ladder is too limiting and, besides the safety factors, you could get a blotchy appearance because you can't work larger areas. In addition, like all construction jobs use proper eye wear because getting splashed in the eyes with a stucco mixture can get you a trip to the hospital

Underlay: Stucco dries to a hard compound so it is imperative to have a solid base that will not move. On wood-framed structures the exterior is usually wrapped with a standard house wrap that can allow moisture to escape. Some contractors prefer 15 pound roofing felt. Then a wire mesh is stapled to the surface and the standard size for this is 17 gauge.

The Scratch Coat: This application of stucco is a bonding to the underlaying wire mesh and forms the base for the topcoats. The mixture for the scratch coat, which can be done in a wheelbarrow or large bucket, is usually: 1 Part Portland Cement; 1 Part Hydrated Lime; 2 ½ to 4 parts sand. Water is added carefully and the mixture is stirred with a wand attached to an electric drill for eve n mixing. There are premixed bags of stucco but doing it yourself is much cheaper. This is not a 1-man job. Mixing the mud and applying it creates a time lag and the stucco may prematurely dry while you are mixing your next batch creating a noticeable line between batches. Besides, stuccoing and mixing are hard work and your performance on the wall could wane over time.

Just do one wall at a time so that the stucco does not harden. The “mud” is pressed into the wire mesh with a trowel so it extrudes through to the wall then it is smoother over with the trowel so that I covers the mesh by a minimum of about ¼.” Now take a grass rake or plaster's rake and sweep grooves about 1/8” think on the surface. Allow to cure 24 - 48 hours.

The Brown Coat: Some masons skip over this step, but it doesn't hurt to spend the time for this process. For the brown coat you will need: 1 part portland cement; 1 part hydrated lime: and 3 1/2 to 5 parts sand. Notice the mix has more sand. This will form the bonding between the topcoat and the anchoring of the scratch coat. Let this cure 24 - 48hours. Wet the surface before applying the coat.

The Finish Coat: Now the sand in the mixture is cut back so that the mud is creamy: 1 part portland cement; 1 part hydrated lime; and 1 1/2 to 3 parts sand. The key to putting on the top coat is that it must be kept moist to avoid cracking. In this process you can color the mixture but mix the dye with water and stir well first, then add it to the top coat bucket as you are stir it with the drill and wand. Wet the surface before applying the coat and then trowel on.

If you are going to put designs on the stucco you can either do this at this stage or you can simply put on a smooth coat and then apply swirls or other features at a fourth stage. Do not let the top coat dry quickly. Take time to spray it 3 to 4 times a day for 3 or 4 days. This will prevent cracking.

Painting Stucco: If you are thinking of painting your stucco wait 4 - 5 weeks so that all of the moisture is out. Start out with a latex concrete primer and either spray it on or brush it. Brushing takes time but will get it into all the crevices. The final coast can be sprayed or rolled with a furred paint roller.

EIFS (Exterior Insulation and Finish System)

EFIS is an exterior wall system that people confuse with actual with stucco. In reality it is not a stucco or even a concrete derivative. It just looks like it is and that is why it is used on commercial projects. EIFS systems have foam board for a base with a fiberglass mesh attached to it. This is then coated with a stucco-like finish. As it is installed as a system it requires special training to install.

Posted by: TrustedPros
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