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Dom>disclosure>Canadian Architectural Digest> CBD-19. sealing
Originally published in July 1961E.V. Gibbons
Noah is said to have used bitumen as a sealant when building the ark. Watertightness and weatherproofing of the structure must still be carefully considered.
Although asphalt shingles continue to play an important role, they are only one of many such building materials widely used in construction today. The development of new materials, combined with new construction methods, has increased the importance and reliance on sealing compounds that prevent water ingress. The purpose of this article is to describe the composition and properties of many of these materials, the significance of the tests used in their evaluation, and to include application recommendations to extend their service life.
Because of the different properties that can be obtained from the many different materials used to make sealing compounds, it can be difficult to categorize sealing compounds into specific types for specific applications or based on ingredients. There are generally two fairly broad classifications - one for adhesives and less elastic sealants, and the other for the more recently developed high molecular weight elastomers. From a designer's perspective, a more significant distinction between types can be made on the basis of weathering elongation, as this property must first be considered when selecting a grout for a particular grouting application.
The ability to hold in place and provide a seal in joints while subjected to relatively large deformations are the primary properties of sealing materials. The amount of movement that occurs in the joint, related to the width of the joint, will first determine the type of material that can be considered for a particular application. In situations where little or no joint movement is expected, traditional raw linoleum may even be satisfactory. The requirement for moderate movement in fairly wide joints has long been a common requirement in civil engineering and can often be met with adhesives made from treated drying oils which give about 10% elongation after the Rate atmosphere. Polybutylene, butyl and neoprene grades provide up to 50% useful stretch. If extreme joint movements in tight joints must be considered, it may be necessary to use highly elastic joints, such as those made of polysulfide polymers or silicone rubber that give more than 100% useful elongation in weather conditions.
When large variations in seam width are allowed, the choice is to use a medium or low expansion in wide seams or a highly elastic material in narrow seams. More often, other considerations may influence the choice of joint width, so a material must be selected that will provide an appropriate minimum percentage of elongation determined by the ratio of expected joint displacement to width.
In addition to the elongation requirements mentioned, there are a number of inherent properties that a sealant must have in order to perform its function properly. It must be cohesive and adhere well to the material on which it is applied. Workability at different temperatures is also essential to ensure proper joint filling and a smooth, uniform surface. When applied and exposed to the atmosphere, it should form a non-sticky, tough, elastic skin over the flexible inner fabric. The leather protects against dirt and can be dyed. During the aging process, it is essential that the sealant retains its flexibility with minimal shrinkage. In general, when these materials are applied to porous walls, they must have non-staining properties and must be resistant to alkalis. The primary sealing layer retains these properties and is expected to last more than 10 years.
Although linoleic putties are used almost exclusively for glazing wooden window frames, they are technically used as sealants that act as sealants to prevent water ingress. They have had good results for a long time and are still widely used. They are only available in a knife grade consistency, unlike many other sealants used for glass which are available in a gun grade consistency. Putty is obtained by thoroughly mixing finely ground calcium carbonate (white powder) and raw linseed oil. They tend to harden and become quite brittle over time, but their life can be greatly extended by priming the wings before use and following a good paint maintenance schedule.
Joint glue consists of carrier, solvent, drying agent and mineral stabilizer. If color is desired, appropriate pigments must be included. It is the carrier that provides the bonding and sealing properties and is usually in the form of a drying oil, such as soybean or linseed oil, which absorbs oxygen from the atmosphere and forms a dry film. These oils have the property of increasing viscosity when heated under controlled conditions. Drying oils are often heat treated when grouting, since drying oils are thicker in consistency, giving better control over their tendency to "drain" and stain porous surfaces. Cars often contain non-drying oils to soften and help sealants retain their flexibility over time. Drying agents are added to accelerate the rate of skin formation through oxidation of the drying oil. These are metal salts of naphthenates or linoleates.
Mineral oil solvents are used to adjust the workability of the seal, reducing the viscosity of the carrier and significantly improving the ease of manufacture. Excess solvent should be avoided, although it may be necessary to add solvent to the job when the plaster is too hard or when the working temperature is low. If the oil is too thin, it can cause staining, and the subsequent evaporation of the solvent can cause shrinkage and cracking. Add mineral stabilizers, such as asbestos fibers, to hold the seal in place, especially in vertical joints, immediately after application and before it hardens. Fine limestone filler increases stability by reducing shrinkage.
The above materials are oxidizing adhesives and are used on exposed areas where painting may be required. They must be used with materials with a low coefficient of thermal expansion that do not elongate more than 10% when grouted. They are ideal as a general sealant for weather sealing around windows and doors and for sealing joints between wood and walls.
Polybutene and bituminous sealing compounds do not oxidize. They solidify when the solvent evaporates. Both are available in different consistencies. When mixed with fillers and stabilizers, they provide excellent performance, do not require skin, and are highly desirable for maintaining plastic consistency. Such applications include use as a base seal for metal cladding, lap joints and sealing hidden joints between timber and walls. In semi-exposed areas and where solvents can escape, these seals will harden as they shrink. Bitumen can also be mixed with semi-drying oils and colored to make a superior gun material and can be used when dark colors are acceptable. Made from medium molecular weight polybutylene, the sealant has a usable elongation of 50% and remains flexible indefinitely.
High molecular weight elastomeric sealing materials include polysulfide polymers, butyl rubber, neoprene, hypalon, and silicone rubber. Of these, the longest is the most widespread polysulfide type. It is a two-component sealant consisting of a base material and an accelerator. Chemical curing begins with a polymerization reaction when mixed well before use; curing speed increases with temperature and humidity. The material does not contain solvents and after solidification is a soft rubber without shrinkage. It adheres well to a variety of building materials and is widely used in curtain wall construction to seal critical areas where high stretch may be required. It will harden slowly over time, but will last more than 25 years. One-component polysulfide mastic is also supplied. It will not set or harden and is used where elasticity is not required.
Silicone sealant is a one-component sealant that hardens when applied and exposed to air. It also has excellent adhesion properties and can be used where high stretch properties are required. Available in a variety of colors, this sealant has good weather resistance with minimal shrinkage. Butyl, Neoprene and Hypalon sealants are solvent-based sealants made from fillers and pigments, so they come in a variety of colors. Despite their much higher shrinkage properties, butyl rubber and neoprene compounds still offer advantages over polysulfide materials. Hypalon material has many desirable sealing properties, but unfortunately little has been reported on its long-term effectiveness.
the meaning of the test
Several test methods have been developed to help determine the quality of a sealant and its suitability for various needs. Currently, it only applies to those methods that regulatory bodies such as the Canadian Government Code Council have accepted as more or less standard methods. Details of the various test requirements and methods used are contained in the relevant C.G.S.B. Specifications are listed at the end of this article. Unfortunately, there are no short-term tests that can be used to definitively predict long-term performance.
Quality of work:General requirements to ensure uniform and uniform quality, which can be easily cut with putty compounds without chipping or scraping, and which retains its shape after application. The sealant should be fluid enough when applied to completely fill the cavity. However, in case the material is too liquid and tends to sink or flow in vertical joints, the sink test can be used. This is done by placing the material being tested in a 1/2 x 3/4 inch container. channel and measure any deflection that may occur.
flexibility: Includes a bend test to determine if the sealant tends to lose adhesion or crack after exposure to alternating wetting cycles and a range of drying temperatures. Its ability to maintain tensile properties can also be measured and is of particular interest given the same usage requirements. A test of the ability of highly elastic types of sealants to withstand repeated bending during use was also developed. In this test, the gasket is applied to the glass and bent over a range of temperatures (100,000 times per % inch). No loss of grip is allowed. The test simulates in an accelerated manner the cyclic conditions under which building materials undergo dimensional changes due to changes in temperature and moisture content.
bleeding: This test is designed to measure the tendency of a sealant to migrate when applied to a porous surface. It is important to keep these oils in the sealant to avoid premature hardening and loss of flexibility. Also important in some cases is the effect of oil stains on the exposed brick.
Shrinkage: Sealant shrinkage is associated with loss of oil, solvent and water evaporation by migration or evaporation; excessive shrinkage can affect the appearance of exposed joints, the adhesion and hardness of the sealant.
hardness: All sealing compounds harden over time. Evaporation of solvents and light oils, polymerisation of drying oils and chemical reactions between different components are some of the factors that can affect hardness and final adhesion. Good resistance to UV radiation is required to avoid hardening, especially important with drying oils and polysulphides. Resistance can be increased by proper selection of materials in the formulation and maintenance after use. The standard method for determining hardness is to use a Shore A durometer. The new material will usually be within 20 to 35 units of the gauge mark after application and curing. The normal rate of curing is about one unit per year, so after 30 years, unless accelerated, the material is still quite flexible and ready for use.
Despite the emphasis on achieving quality sealant, the value of a quality material can be lost if not applied correctly. All surfaces on which these products are applied must be dry and clean without exception. Their future performance will be directly related to their initial commitment. When designing sealing openings, it is not only important that they are the right size and shape, but also that they are properly inspected for cleanliness.
Considering the size of the joints, it is necessary to pay attention to the movements that can occur in them. Since temperature ranges in excess of 100°F are not uncommon in any part of Canada, there have been many reported cases of complete closure of joints at high temperatures. Therefore, the relative position of the metal profiles that make up the assembly should be determined in extreme conditions that may occur. The size of the notch to accommodate the glass and gasket must be carefully thought out. Determining the thickness of the sealant required to withstand temperature and pressure induced displacements must be determined in order to minimize stress and thereby extend the life of the sealant. Many suppliers do not want their material to be compressed more than 50% even though its stretch is well over 100%. This is understandable given the repetitive nature of joint movements.
With metal, it is important to completely remove the paint from the area where the sealant is being applied. This is essential for clear coatings applied to aluminum alloys. Porous masonry or wood surfaces can be improved by applying a primer after cleaning. If more than one type of sealant is used in a joint, they must be compatible or they may react and seriously stain the exposed surfaces. Since UV radiation promotes the degradation of many sealants, it is often necessary to paint the surface after application.
A gasket is needed to seal and allow movement in many conditions. They are often the only line of defense against water penetration, and the success of other building materials often depends on them. Although the amount of sealant used in buildings is relatively small, it is important enough to require the most careful attention in joint design, material selection, use, and maintenance.
The Government of Canada Board of Caulk specifications are as follows:
|19-GP-1||kits; a type of linseed oil, used for glazing.|
|19-GP-3||Connections; grouting and glazing, elastomers, types of chemical hardening, gun quality.|
|19-GP-4||Connections; sealants, elastomers for marine use.|
|19-GP-6||Connections; seal, oil-based, for weapons.|
|37-GP-5a||plastic; reduction of asphalt.|