The finish coat about 18 inch thick is applied over the previous two coats totaling about 38. Scratch coat mortar tds198 surfaces must be structurally sound, clean, dry and free from grease, oil, dirt, curing compounds, sealers, adhesives or any other contaminant that would prevent a good bond. Vibration causes cracking in concrete as well as stucco. Apr 10, 2020 if the scratch coat is not scratched, the next stucco coat may not adhere correctly. 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. Jul 23, 2008 for example, if the brown coat is applied to a scratch coat that hasnt sufficiently cured yet, it will cause the scratch coat to absorb water from the brown coat and continue to cure. 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. Excessive troweling or movement of the scratch coat must be avoided, because too much action will break the bond between the plaster and masonry.
This coat is then moistcured morning and evening for 48 hours in preparation for the finish coat. The various layers that make up a stucco exterior wall finish contain basically the same ingredients, but are mixed at different ratios. If stucco finishing is done using a trowel, the walls need to be cool and moist with no standing water. Extra curing time improves strength and minimizes cracking. Excessive or fast evaporation of water from the cement plaster will.
Faulty stucco installation no matter how great the quality of the stucco is, if its not installed right, the outcome will still be mediocre. In hot or dry climates or windy weather, keeping the stucco moist during the curing. Excess water in the scratch coat may cause future cracks in the finished surface. Taken together, the scratch coat and brown coat are called the base coat. This application of stucco is a bonding to the underlaying wire mesh and forms the base for the topcoats. This acts as an ideal base for the finish coat, which is integrally colored in most cases and is what you see on stucco, so the base needs to be uniform. For proper curing, the scratch coat needs to be kept moist by misting or fogging with water for 48 hours. Around here, chicken wire is the trade term for stucco lath. The slower the scratch or brown coat cures, the less likely it will crack. The structural are the ones we see most because they are large and very common. Stucco cracking in portland cement plaster base coats parex. If vapor permeable finish coat is used, the cement base coat will cure regardless of how soon the finish is applied. Improper composition or curing means you might have to deal with water leaking through your walls or cracks forming. It is important that the scratch coat be properly cured before the application of the brown coat, to minimize the cracking.
A house clad entirely in stucco is a thing of beauty. We are often asked if stucco and plaster are the same thing, and if plaster and exterior insulation finishing systems eifs are the same thing. Cement needs to set and harden, curinghardening occurs through hydration. The two coats, which are curing, drying and shrinking at the same time, will act as one coat, doubling the amount of stress they place on the stucco system.
The plaster must be applied with sufficient force to fully adhere it to the masonry. The initial scratch coat must fully encapsulate the metal lath to provide an. The one coat synthetic turned me off because you can not only jam a pencil right through a house with this installed but the problems associated. Stucco cracking is an issue that homeowners ask me about all the time. Curing is a stucco application process that can last several days. It is usually recommended that the each of the two or three layers of stucco cure for 36 hours or more.
This could be due to the plaster drying too quickly, too much water being present in the mix, or the plaster was applied when it was too hot or too cold outside. Moistcuring can be terminated after 48 to 72 hours, but the finish coat should remain uncoated for at least seven days to prevent coating failure or poor bonding. Stucco is a traditional exterior finish material, typically three coats of. Internal stresses are due to the natural curing and drying process of stucco. Identifying various cracks in stucco the stucco guy. When the base coat doesnt cure properly, it means the plaster did not dry and settle into place correctly. So, be extra careful not to miss this kind of stucco crack. This stucco system consists of a scratch coat, brown coat and finish coat. Hot and cold helpful tips for placing plaster stucco materials in hot and cold conditions weather has a significant effect on the application requirements and nuances of plaster stucco seasonally and it can sometimes be daily. This article will give you some helpful advice on how to properly mix stucco. Reentrant cracks are the hairline cracks that can appear at comers of square openings in the stucco such as windows.
For best results, apply the stucco mix within a temperature range of 4080 degrees fahrenheit. What is the wait time for a scratch coat before applying. There are premixed bags of stucco but doing it yourself is much cheaper. This permits complete curing of both the scratch and brown coats.
Oct 03, 20 plastering first coat of plaster scratch coat for beginners. Finally, if the stucco is not cured in the proper manner, it could become brittle. I put the builder on notice and of course the warranty has. Repair of portland cement plaster stucco a a a a aa aa a a a a a aa a a a a a finish coat brown coat scratch coat metal lath building paper fig. Installers add decorative textures and color during the finish coat. Sep 20, 2011 caulking hairline cracks in new stucco. Although not all cracks are objectionable, cracks in stucco acceptable to one person might be unacceptable to another person. The mixing and application process, if done properly will help minimize cracking and when it comes to stucco, the fewer cracks the better. The main cause for this stucco crack is from the base coat not curing properly. Jan 24, 2019 the scratch coat should be 38 thick, and it should cure for 48 hours before the brown coat is applied. Once the coat has chemically reacted with a sufficient amount of water and is allowed to dry, it reduces in volume and shrinks. Shrinkage cracks are the ones that look like a honey comb or spider web cracking on smooth coat stucco. In a traditional threecoat stucco system, the finish coat must be cured using the same practices as base coats.
Jan 06, 20 in a traditional three coat stucco system, the finish coat must be cured using the same practices as base coats. A break in the threecoat stucco scratch coat, brown coat, and the finish coat application, for instance, will cause a big. This type of cracking is basically a sign that the base coat did not cure properly. Damp cure cement plaster in hot, dry weather, do not soak walls.
In hot or dry climates or windy weather, keeping the stucco moist during the curing period may require frequent wetting. If the scratch coat is not scratched, the next stucco coat may not adhere correctly. The two types of stucco cracks are structural and shrinkage. After scoring the surface, it is best to let the surface cure for 10 to 12 hours. Now that you know why stucco cracks, lets find out how serious a stucco crack can be. The rate and length of this moist curing period may vary with the weather. Now in the winter i am seeing more and more hairline cracks and some spider cracks but still hairline. The third step in a threecoat stucco system is the finish coat. To ensure proper curing, keep the repair damp for at least two days by spraying. In contrast, when a coat is insufficiently hydrated, it cant cure properly. After a coat of stucco is applied, it should be hydrated to allow the stucco to cure to full strength. While timing will vary by project, this should be used as a basic guide.
The scratch coat should be 38 thick, and it should cure for 48 hours before the brown coat is applied. There are a few difference between a stucco scratch coat and a brown coat. Hello everyone, i have a 5 year old home that had a few hair line cracks the first year. The scratch coat is followed by whats called a brown coat. 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. Drying time is a factor in the development of cracks. May 02, 2015 hydrating or wetting walls prior to color coat, properly curing stucco plaster geek, stucco nerd, need a life stucco dude thanks for watching and have a fantastic day. The shrinkage builds up stresses in the coat, which are released as a series of micro cracks. These cracks typically run diagonally from the apex of the comer of the opening. Hard float the brown coat to densify plaster membrane. Plastering first coat of plaster scratch coat for beginners. I would really appreciate if you can share your expertise and let. The mixture for the scratch coat, which can be done in a wheelbarrow or large bucket, is usually. Be patient and properly slowcure moisture applied the stucco.
Sure enough, it always cracks, no matter how i cure it, and no matter what time of year. 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. It generally indicates a lack of moist curing, without moist curing it will be weak in the time soon after application when external stresses can cause cracking. Hot and cold helpful tips for placing plasterstucco materials in hot and cold conditions weather has a significant effect on the application requirements and nuances of plasterstucco seasonally and it can sometimes be daily. Continue reading taxes, death, and cracks in stucco walls. Observations of numerous building envelope failures in stucco i. For example, if the brown coat is applied to a scratch coat that hasnt sufficiently cured yet, it will cause the scratch coat to absorb water from the brown coat and continue to cure. A very simple recipe for a stucco scratch coat consists of 3 parts sand to 1 part cement. The scratch coat can be applied either from the bottom to the top of the work area, or from top to bottom. Cracks that appear within the first 30 days after installation and are larger than 116 the thick. Read about how cracks occur in 3coat stucco systems and some of the best. As you might have guessed from the name, this type of stucco crack resembles a spider web on your siding. Stucco cracking in portland cement plaster base coats.
While there are several parts of the north america where stucco always has a strong presence, there appears to be a general renewed interest in portland cement plaster for building finishes everywhere. Locate and construct control joints as in threecoat stucco systems described earlier in this section. The first stucco coat is called a scratch coat and as its name implies, it has a rough surface so the next. Then i have a choice of three coat stucco scratch, brown, color, two coat brown, color then electromeric paint, or synthetic stucco. Sep 12, 2016 reentrant cracks are the hairline cracks that can appear at comers of square openings in the stucco such as windows. 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. Rainy, high humidity weather will require less wetting that will dry, windy conditions. After you have applied your scratch coat to a uniform thickness all over your surface, you will immediately want to scratch the surface. Except in very moist weather, misting should start as soon as the freshly applied stucco lightens in color and be repeated at the start and end of each day until the. Lime and other things can also be added but arent usually needed.
In the recent past, one week was common for curing. 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. Improving stucco durability using moistcuring page 2 of. Moist curing can be terminated after 48 to 72 hours, but the finish coat should remain uncoated for at least seven days to prevent coating failure or poor bonding. When a base coat is soft there is a cause for concern. I am currently in the process of stucco ing my house. Water is added carefully and the mixture is stirred with a wand attached to an electric drill for eve n mixing. The brown coat is followed by the finish or color coat. 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. Stucco is designed to carry and bind the aggregate, bond in place, and get hard. 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. Tips on applying mortar scratch coat for bathroom tiles.
The brown coat may be reinforced with a variety of fibers, and it must be trowel. They ranged any where from 45 feet long to the length of my garage wall 16 plus feet between the front windows. While the ubc allows the application of the finish coat seven days after the brown has. The wire is nailed over black felt paper it actually comes in sheets or rolls, with the wire glued to the paper, and serves to reinforce the stucco. This is caused by either drying too quickly, too muck water in the mix, or mixed incorrectly or applied when it was too cold or too hot the day the stucco was applied.
There are two fundamental types of stresses that cause stucco cracksinternal and external. Ideally, you should allow a week to pass before finishing the stucco. It is very subtle, which can make it difficult to spot with the naked eye. The brown coat surface is much smoother than the scratch coat and is gritty to the touch but flatter and looks more appealing than the scratch. After my contractor applied the brown coat its been over a week now i see a lot of hair line cracks and lines on one of the walls. Small cracks can be filled simply with a coat of paint, while thicker cracks may be. The most critical period for moist curing of exterior portland cement plaster is the 48 hours immediately subsequent to the application of both the scratch coat and the brown coat, a fact noted in building codes. Sep 12, 2019 this coat is then moistcured morning and evening for 48 hours in preparation for the finish coat. We have hairline cracking on a new 3 coat system, we waited several weeks between coats for curing, seems to be getting worse but cracks are less than 2 question is what caused it, will it slow down and stop, too many to score and patch, can we use a heavy coat of polymer primer to fill in cracks then wait and do a final coat of paint. When patching plaster, each succeeding coat is cut back further than the preceding coat, the base coat being the smallest area and the finish coat being the largest area to be patched. Make certain to cure the scratch coat for at least 24 hours before applying the finish coat. Multiple hairline cracks in stucco home inspection.
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