Among the many factors that influence color in stucco applications is substrate suction and hydration i. The finish is where the texture andor color is added. A scratcher tool is used to get the horizontal lines in the cement and a green float is used. Portland cementbased plaster is such a material that uses portland cement as the binder. If cracks exceed 332 it is unacceptable and should be repaired. Learn how to tell if the cracks are a problem and if so what to do about them. The finish coat about 18 inch thick is applied over the previous two coats totaling about 38. Our recommended tools, greeting our ambitious and faithful subscribers, as well as fellow plasterers. While timing will vary by project, this should be used as a basic guide.
One of the most common problems is cracked stucco and with the trend of using the material as a cladding, the situation will get worse. The scratch coat can be applied by hand or by machine but its surface layer must have horizontal or crisscross pattern troweled into it for added stability of the next layer. These cracks typically run diagonally from the apex of the comer of the opening. Plywood installation is probably the leading cause of cracks in stucco. Curing is a stucco application process that can last several days. Stucco is a somewhat colloquial term for portland cement plaster, and. Yes, if you paint the fresh stucco i would give it as much time as possible both for curing and for settling and shrinkage cracks to develop so you could have them repaired as part of the paint job 3. The first layer is allowed to fully cure before the second is added.
Ideally, you should allow a week to pass before finishing the stucco. Astm specifications, coatings, construction techniques, plaster, stucco introduction portland cementbased plaster has many useful applica tions. Damp cure cement plaster in hot, dry weather, do not soak walls. The shrinkage builds up stresses in the coat, which are released as a series of micro cracks. Make certain to cure the scratch coat for at least 24 hours before applying the finish coat. Improving stucco durability using moistcuring page 2 of 3. Portland cement stucco cracks develop for many reasons. Hard float the brown coat to densify plaster membrane.
How to prevent stucco from cracking professional builder. Application of the finish coat before the base coat has properly cured. The first coat is allowed to dry cure before the second layer is applied. The rate and length of this moist curing period may vary with the weather. Stucco repair brown coat applied less than 24 hours. Remove all loose or otherwise damaged stucco in the repair area by. If theyre larger or more complicated than you thought, then call in an expert to take a look at them. Concrete masonry or brick is the ideal foundation for plaster and is the. Stucco is by nature hard and strong, but it is relatively thin and brittle and will crack when subjected to stresses that exceed its tensile strength. The scratch coat for my homes exterior walls was applied a few days ago and in the evening of the first day i noticed cracks forming over top of where the wire mesh is located beneath the scratch coat. Stucco, cracking, plaster basecoat, portland plaster. May 19, 2020 if the scratch coat is not scratched, the next stucco coat may not adhere correctly. Start hanging the building paper at the bottom of the. If the scratch coat is not scratched, the next stucco coat may not adhere correctly.
Once moisture or water gets inside a wall, it will inevitably cause further damage. Improving stucco durability using moistcuring page 2 of. Plaster is the general term for material that is applied to a wall surface in a thin layer. Drying time is a factor in the development of cracks. What is the wait time for a scratch coat before applying. The scratch can be applied with a hawk and trowel, or sprayed on.
Patching of hairline cracks is not recommended as it will detract from the natural beauty of the stucco and will serve no useful purpose. In a stucco project, after you have applied a scratch coat to your surface, there are some basic guidelines to follow before applying a brown coat. Reentrant cracks are the hairline cracks that can appear at comers of square openings in the stucco such as windows. Once the coat has chemically reacted with a sufficient amount of water and is allowed to dry, it reduces in volume and shrinks. This permits complete curing of both the scratch and brown coats. The first layer of plaster is called a scratch coat, consisting of plastic cement and sand. Jan 06, 20 observations of numerous building envelope failures in stucco i. In hot or dry climates or windy weather, keeping the stucco moist during the curing period may require frequent wetting. On any stucco job, you have to expect both the scratch coat and the brown coats to have minor cracking from shrinking.
Conversely, texas bureau of lathing and plasterings tblps systems manual does not require moistcuring when the humidity in the air is over 75 percent. Jan 06, 20 for example, northwest wall and ceiling bureaus nwcbs stucco resource guide only suggests curing the first i. Excessive cracking, however, usually means something was done improperly for example, the mix may have been too rich too much cement, the stucco layers may have been too thick, or the walls may. It is usually recommended that the each of the two or three layers of stucco cure for 36 hours or more. If vapor permeable finish coat is used, the cement basecoat will cure regardless of how soon the finish is applied. While the ubc allows the application of the finish coat seven days after the brown has. Apply a coat of concrete bonding agent to the concrete surface using a paintbrush.
Jul 23, 2008 after a coat of stucco is applied, it should be hydrated to allow the stucco to cure to full strength. Sep 12, 2016 reentrant cracks are the hairline cracks that can appear at comers of square openings in the stucco such as windows. The mixture for the scratch coat, which can be done in a wheelbarrow or large bucket, is usually. In some areas the cracks only follow the horizontal wires in the mesh, but in other areas the cracks are forming along both the horizontal and. Sep 20, 2011 cracks in stucco are natural and arent considered to be a big deal, just sometimes unsightly. When the brown coat is dry then the final finish coat is applied.
Multiple hairline cracks in stucco home inspection. With stucco cracks, its always best to tackle them as soon as you see them. Allow the stucco to firm up, then scratch the surface with a nail. After you have applied your scratch coat to a uniform thickness all over your surface, you will immediately want to scratch the surface. These cracks typically run diagonally from the apex of the corner of the opening. A short delay between the first and second coat helps to create a good bond between the two and strengthens the scratch coat by rewetting it for a more complete cure.
In contrast, when a coat is insufficiently hydrated, it cant cure properly. The finish coat about 18 inch thick is applied over the previous two coats totaling about 38 inch, so any hairline cracks are now covered. Jan 24, 2019 the scratch coat should be 38 thick, and it should cure for 48 hours before the brown coat is applied. If vapor permeable finish coat is used, the cement base coat will cure regardless of how soon the finish is applied. To this end, we water cure our scratch coat once after 24hours and then again just prior to our brown coat application which should have between 710 days curing time is dusted with water every 48 hours, to enable the brown to actually cure sufficiently.
Hairline cracks in this color coat are inevitable, but if the base coats are well cured, these surface cracks will not communicate water through the stucco. Improving stucco durability using moistcuring construction. Finally, if the stucco is not cured in the proper manner, it could become brittle. Although not all cracks are objectionable, cracks in stucco acceptable to one person might be unacceptable to another person. In the southwest, where adobe is popular, the brown coat is often steel.
This application of stucco is a bonding to the underlaying wire mesh and forms the base for the topcoats. Mar 03, 2016 now that you know why stucco cracks, lets find out how serious a stucco crack can be. Ncma tek national concrete masonry association an information series from the national authority on concrete masonry technology plaster and stucco for concrete masonrytek 93a mortar, grout, stucco 2002 keywords. What is the wait time for a scratch coat before applying the. Identifying various cracks in stucco the stucco guy. Now that you know why stucco cracks, lets find out how serious a stucco crack can be. Other common repair methods may be better suited to active cracks. Small cracks can be filled simply with a coat of paint, while thicker cracks may be cauked. Any cracks larger than 1 116inch in the brown coat should be patched before the top coat goes on. The cure time between the scratch and brown coat in a portland cement. However, they can provide a pathway for moisture and water to enter into a wall system. A trowel is used to scratch the surface horizontally or in a crisscross pattern to provide a key for the second layer. The slower the scratch or brown coat cures, the less likely it will crack. Scratch the coat use a notched trowel to scratch grooves into it, which will allow future coats to better adhere to the first layer.
May 01, 2015 hydrating or wetting stucco walls prior to applying a color coat. These hairline cracks in no way compromise the integrity of the plaster coat nor shorten the useful life of the product. Be patient and properly slow cure moisture applied the stucco. Should stucco walls breathe or be sealed with paint. It generally indicates a lack of moist curing, without moist curing it will be weak in the time soon after. The process, in a nutshell basically the three coat system consists of paper and wire, a scratch. Fixing 10 mediumsized cracks takes about 15 to 20 bags of stucco. The same stucco material may result in a different color in a humid environment than in a dry area or in shady versus sunny areas. Internal stresses are due to the natural curing and drying process of stucco. By code, builders should provide at least 48 hours of curing time after the first coat is applied and wait seven days after the second coat before applying the finish. The scratch coat should be 38 thick, and it should cure for 48 hours before the brown coat is applied.
After a coat of stucco is applied, it should be hydrated to allow the stucco to cure to full strength. When is it time to repair stucco cracks in the walls. Yes, stucco can be painted if you choose to do this, make sure to use the right kind of paint and prep 2. Cracks caused by plywood are distinguished by the directions they take. After you have applied your scratch coat to a uniform thickness all over your surface, you will immediately want to scratch the surface horizontally to create a better surface for the next coatthe brown coatto bond to the surface. Once the crack has been filled, fogcoat may be used to even out the color around the repaired area. Cracks that appear within the first 30 days after installation and are larger than 116 the thick. Smooth it out smooth the stucco mixture with a finishing trowel and pack it against the edge of the existing stucco surface. A brush is not used because it will cause delamination. In hot or dry climates or windy weather, keeping the stucco moist during the curing.
Locate and construct control joints as in threecoat stucco systems described earlier in this section. Also, if interested in the stucco plastering tools we recommend visit our amazon link at. The first stucco coat is called a scratch coat and as its name implies, it has a. This way, youll keep your stucco in good condition for years to come. Stucco cracking in portland cement plaster base coats parex.
This stucco system consists of a scratch coat, brown coat and finish coat. The scratch coat should be 38 thick, and it should cure for 48 hours before the. There are two fundamental types of stresses that cause stucco cracksinternal and external. This type of cracking is basically a sign that the base coat did not cure properly. A one coat stucco would be about 38 inch thickness stucco over a wood substrate should be 34 to 78 inches in thickness. When a base coat is soft there is a cause for concern. The brown coat in the stucco process is applied over the scratch coat mostly but can also be applied over cement based substrates as well, like the scratch coat. Repairing stucco cracks, why new stucco walls can crack youtube. After scoring the surface, it is best to let the surface cure for 10 to 12 hours to make sure it has. Consult the stucco finish manufacturer or contractor for recommended repair methods.
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