Pcas book, fiber reinforced concrete, states that it was the predominant form of fiber cement composite when it was developed in the early 1900s. That could be a portland cementbased paint or a slurry of cement and pigments, sometimes call a fog coat. Hardcoat stucco cracks, leaks, damage stucco cracks, leaks at control joints, standards. The plastering contractor thinks the walls were subjected to excessive moisture,rain penetrating to the osb then baked by the sun, then expanded and contracted to crack the stucco. Portland cement stucco is very hard and brittle and can easily crack if the base on. Stucco may be used to cover less visually appealing construction materials, such as metal, concrete, cinder block, or clay brick and adobe. Stucco, make up of sand portland cement, and water is a protective coating but is not of itself a. We have excessive cracking in a 3 coat stucco system placed over osb shear panel.
Stucco manufacturers association is a nonprofit trade association whose purpose is to educate the building industry and the public about the quality use of stucco and best practices of stucco application. Dryvit walls, also known as eifs or exterior insulation and finish system, provide additional insulation to exterior walls with an appearance that is very similar to stucco. Improper curing of plaster can result in map cracking. Every contractor who has anything to do with stucco knows the frustration of hairline cracks that are inherent with a cement stucco system. It allows for a wide expression of aesthetics, is a cost effective finish, is durable in all types of climates especially wet ones, and offers fire resistance. This shrinkage, when restrained, may create hairline cracks. The january 2007 article on stucco cracks dealt with myths, planning, caveats and suggested contract language when working with such systems. Stucco is a mix of portland cement, water, lime and sand. Remove product item description unit price quantity total price details. Fill the crack with knifegrade elastomeric crack filler cr214 sto flexible crack filler and follow procedure a or b above.
Our industry is of the opinion that portland cement plaster should have a. Stucco manufacturers association educating the building. With the advent of fiberreinforced portland cement, stucco systems today are very often twocoat systems a base and finish coat, but often referred to in the industry as one coat stucco, rather than the threecoat systems of yesterday a scratch, brown, and finish coat. Stucco consisting mostly of portland cement generally will not be physically compatible with the softer, more flexible, limerich historic stuccos used throughout the 18th and much of the 19th centuries. This howto guide and technical manual contains everything you need to know about plastering and stucco. To repair excessive stucco cracking on existing walls, the aplc. More reasons stucco cracks lack of control and expansion joints. External stresses are due to the transfer of outside forces into the stucco assembly. If you can relieve large spans of stress, youll prevent large cracks. Stucco crack repair explained by professional stucco. The set up so, you have installed a cement or hard coat stucco. How to make and mix portland cement stucco in a wheelbarrow.
The stucco manufacturers association sma is a nonprofit association formed in 1957 to promote best practices for cement plastering stucco. A fresh concrete mixture is a fluid, plastic mass that can be molded into virtually any shape, but as the material hardens there is a reduction in volume or shrinkage. Asbestos and old concrete concrete construction magazine. It provides an economical hard surface that is rot, rust, and fire resistant, which can be colored and finished in a wide range of textures to adorn any architectural style. Its composed of portland cement the same material that lends strength to concrete driveways and slab foundations. A portland cement, sand and water mix first developed by the romans used for its durability and low maintenance. Cracks in stucco are caused by stress to the underlying membrane. Astm standard c 926, specification for application of portland cement based plaster, permits direct application of stucco to solid surfaces like concrete and masonry as long as bond is sufficient. Astm c 926, standard specification for application of portland cement.
From time to time, even stucco manufactured and installed correctly will crack. Stucco installation standards portland cement association. Stucco manufacturers association guide specificationiton. A parging material comprised of one part portland cement and 3 parts sand by volume passing a no.
Over the last century, the plastering industry has had many experts on lath, cement basecoats and the stucco or acrylic finish applied for final decoration. Jamie farny at the portland cement association pca says, asbestos fibers were used in some concrete products in the past. The stucco manufacturers association sma is a non profit association formed in 1957 to promote best practices for cement plastering stucco. Stucco wall methods and choices best practices guide. Mix 23 12 pounds of portland cement with 2 23 pounds of hydrated lime and 1 cubic foot. If cracks exceed 332 it is unacceptable and should be repaired.
Portland cementbased plaster, commonly called stucco, has long been and continues to be a popular choice for finishes on buildings. Stucco, cracking, plaster basecoat, portland plaster. Portland cement plaster can deteri orate for a variety of reasons, including inadequate design details, poor installation, or the use of improper materials. 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. In many cases, damage results from water infiltration into the building structure either through cracks, through the roof, around chimneys, or through window and door openings. The sma and member plastering contractors are constantly striving to improve stucco.
The stucco manufacturers association sma guide specification for 3coat portland cement plaster stucco applied to framed walls 22017 introduction. Waterdamaged plaster often bulges or falls away from. A thick wet mixture of portland cement and water, with or without aggregate, dashed onto the surface of stucco base, such as smooth monolithic concrete or concrete blocks, to improve the mechanical key for subsequent stucco coats. Stucco manufacturers association promotes stucco education in the building industry. Portland cement stucco cracks develop for many reasons. Stucco is a type of cement plaster that can be on interior or exterior walls. Astm specifications, coatings, construction techniques, plaster, stucco introduction portland cement based plaster has many useful applica tions. This article will focus on the investigation of cracks and some suggested repairs. Pca the portland cement association americas cement. Even though stucco is expected to protect your home for over 50 years it is possible for it do get damaged. Like anything else that has cement as its main ingredient it is very rigid. But just like any other construction material that includes portland cement, stucco is prone to cracking. Mix a new batch of stucco using 23 12 pounds of portland cement, 3 pounds of hydrated lime and 1 110 cubic feet of sand.
Stucco frequently asked questions the portland cement. View our series of technical papers on stucco, stucco installation, benefits and crack policy. Plywood installation is probably the leading cause of cracks in stucco. Stucco is by nature hard and strong, but it is relatively thin and brittle and will crack. Portland cement plaster stucco is a building facing material consisting of portland cementbased materials and sand, mixed with water to form a workable mixture. When shrinkage is restrained by contact with supporting soils, granular fill, adjoining. Another reason to recoat a plaster wall is that your building may need a new look, which can be accomplished simply by updating the color.
Top considerations when repairing and repainting synthetic. At worst, the walls may be damaged due to moisture infiltration, building settlement, or other environmental factors. Map cracking on a portland cement plaster stucco wall. As you design and construct stucco projects, you may need some assistance. Much like portland cement concrete, portland cement plaster stucco can develop cracks unless precautions are taken in the projects design stage as well as during the lathing furring, and plastering application.
Stucco trouble shooting chart stucco manufacturers association. Pca portland cement association plaster stucco manual. In this bulletin we discuss some common causes of cracks in cement plaster. The stucco manufacturers association offers the following guidelines regarding stucco cracks. Mix in water just as you did for the first mixture. It is occuring mostly on 2 sides exposed to the sun. At worst, the walls may be damaged due to moisture infiltration. Stucco, the common term for portland cement plaster, is a popular exterior finish for buildings.
For more information about stucco, the portland cement association offers a howto guide and technical manual with indepth descriptions of stucco installations. Here, using a field report of leaks at horizontal control joints in a hardcoat stucco wall system, we describe the inspection, diagnosis, repair, and proper compared with improper installation of traditional stucco building. The differing expansion and contraction rates of lime stucco and portland cement stucco will normally cause the stucco to crack. View cart aptify ebusiness portland cement association. It is strong, durable, waterproof in the common sense of the term, and can be furnished in a wide range of colors and textures. Crack control for concrete masonry walls, tek 101a, national. Astm c 1063, standard specification for installation of lathing and furring to receive interior and exterior portland cementbased plaster solid base for stucco people often ask us if stucco, or portland cement plaster, will adhere to concrete or concrete masonry. Can be colored and finished in a wide range of choices. Technical bulletins stucco manufacturers association.
Though cracks in stucco can occur due to different factors, including wrong mix proportions, insufficient mixing, poor workmanship, seismic movement and seasonal changes, two leading causes. Astm c 1063 standard specification for installation of lathing and furring for portland cement based plaster. This fifth edition, illustrated with numerous color photos, contains essential information on materials, bases, mixes, hand and machine applications, and curing. According to the portland cement association, traditional stucco is a cladding material made from a mixture of portland cement, sand, lime and water. Works well with a cmu and concrete base substrates. Much like portland cement concrete, portland cement plaster stucco can develop. Cement stucco can be thought of as the finish coat of a threecoat cement plaster or the entire assembly as defined by the building codes. On the other hand, synthetic stucco, or eifs exterior insulation finishing system, defines a multilayer system composed of rigid insulation boards fastened to walls and covered with.
Stucco or render is a construction material made of aggregates, a binder, and water. Crack policy technical bulletin 4 stucco is widely used all over the world as an exterior cladding because of its aesthetic appeal, durability, fire resistance, design flexibility, low cost, and ease of maintenance. How to make portland based exterior stucco from scratch in a wheelbarrow. Portland cement stucco a cladding made of sand, cement, and lime has been used to beautify and insulate buildings around the world for centuries. Astm c 926 standard specification for application of portland cement based plaster. Portland cement plaster is classified as a brittle assembly by the building codes and construction industry standards, as such. All portland cement based products, including stucco are susceptible to the. Portland cement adheres well to lots of materials, especially to other materials made from the same type of ingredients. The stucco manufacturers association sma guide specification for 2coat portland cement plaster stucco applied to concrete or masonry walls 22017 introduction. The ubc and astm do not call for a required hardness psi for portland cement plaster.
Threecoat cement plaster or stucco has been in the modern codes since its inception. We try every new product and technique but yet still seem to find ourselves on site with the designer, owner and general contractor pointing fingers at one another for cracks in stucco. Stucco cracking in portland cement plaster base coats. Just like a driveway, though, a stucco wall is prone to cracking, because large areas of stucco cant accommodate expansion and contraction. Plaster is applied either by hand or machine to exterior and interior wall surfaces in two or three coats. Applied in two or more coats to surfaces including masonry and concrete walls, the material is durable.