Patent Publication Number: US-4318258-A

Title: Thermal insulation for buildings

Description:
RELATED APPLICATION 
     This application is closely related to an application Ser. No. 20,509 directed to INSULATING-SLABS AND THEIR USE of the same inventor which is being filed on the same day or shortly before the present application. The entire disclosure of the related application, based on the West German Application No. P 28 50 861.4 filed Nov. 24, 1978, is incorporated herein by reference. 
     TECHNICAL FIELD 
     Insulating-slab elements are used in the construction of, e.g., insulated-plaster facades for buildings. 
     BACKGROUND 
     Throughout the world there is an ever-increasing interest in thermal insulation for buildings. One form of such insulation involves securing foamed-plastic insulating slabs or plates, such as those of foamed polystyrene, to outer surfaces of walls to be insulated. This is conveniently accomplished with mineral plaster or mortar which ordinarily contains at least 5 percent by weight of plastic resin. The outside of the slabs is then covered with a similar plaster or mortar which is suitably reinforced by, e.g., an embedded glass-fiber web, animal hair, cocoa, sisal and/or synthetic fibers. 
     Some difficulty is encountered because the hard-foam slabs are subject to a material degree of shrinkage over an extended period of time, i.e., as residual foaming agent and solvent emanate therefrom. The resulting contraction is more than and in excess of the maximum possible thermal contraction which, in turn, differs from the thermal contraction or expansion of the covering plaster or mortar. Both the shrinkage and the differences in thermal coefficients increase the expectation of cracks and subsequent deterioration of the covering plaster or mortar. 
     In an attempt to minimize this problem, such slabs or plates are usually stored before use for an extended period of time, i.e., until a residual shrinkage of not more than 0.2 percent (2 millimeter per meter) is expected. Even with the use of slabs or plates having a thickness between one inch (2.54 cm) and two inches (5.08 cm), cracking or blistering of the outer plaster or mortar could not always be prevented. The problem increased with increased thicknesses of the hard-foam slab or plate. 
     By using plaster or mortar with a high resin content, the resulting plaster or mortar is elastic and thus has less tendency to crack. Unfortunately, the increase in resin content also makes the plaster or mortar soft. Whereas elasticity is a welcome characteristic, softness is not. Softness is actually highly undesirable for the outer surface of a building. Moreover, plastic resins or similar adhesives increase the water-vapor diffusion-resistance factor of plaster or mortar. When such factor is too high, moisture accumulates in the hard-foam slabs or plates, and this eventually leads to their destruction. However, addition of some resin is highly desirable since pure mineral plaster or mortar does not sufficiently adhere to the surface of hard-foam slabs or plates. 
     INVENTION 
     By using grooved plates, an outer plaster or mortar with a plastic-resin content of less than 3 percent by weight and newly-manufactured slabs or plates or those with a residual shrinkage of at least 0.1 percent, a system was designed to work with hard-foam slabs or plates having thicknesses up to 5 inches (12.7 cm). Stresses created by slab or plate shrinkage were used to &#34;clamp&#34; the slabs or plates to the plaster or mortar, especially with the assistance of plaster-filled grooves. To achieve an uninterrupted &#34;clamping&#34; effect requires forces which are continually larger than those created by thermal expansion and contraction. 
     The limitation of the plastic-resin content in the plaster or mortar is necessitated to limit the water-vapor diffusion-resistance factor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a grooved plate. 
     FIG. 2 is an end view of the plate of FIG. 1. 
     FIG. 3 is an end view of a modification of the plate of FIG. 1. 
    
    
     DETAILS 
     Prior to this time, reinforcement of the plaster or mortar coating applied on the outer side of the hard-foam slabs or plates was regarded as essential, but such reinforcement can now be omitted if the following conditions are satisfied: 
     1. The size and number of grooves (in the slabs or plates) have certain minimal values, depending on slab thickness; 
     2. The residual shrinkage of the slabs or plates is limited to a value between 1 and 4 mm/m, depending on slab thickness; 
     3. The maximum content of plastic resin is 2.5 percent by weight; 
     4. The slab or plate weight per cubic meter is less than 20 kg/m 3 , which was previously considered the minimum. 
     Naturally, satisfactory products are prepared when the weight per cubic meter of the hard-foam plastic is in excess of 20 kg/m 3  and the plaster or mortar is suitably reinforced. To avoid the need for glass-fiber-web or other reinforcement of the plaster or mortar, a delicate balance is maintained between the enumerated conditions. A suitable relationship between the size of grooves, their separation and the residual shrinkage of slabs or plates of different thicknesses is exemplified in Table I. 
     
                       TABLE I                                                     
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Slab                                                                      
or Plate                                                                  
        Distance be-                                                      
                    Groove cross-section                                  
                                   Residual                               
Thickness                                                                 
        tween Grooves                                                     
                    width depth    Shrinkage                              
(mm)    (mm)        (mm)   (mm)    (mm/m)                                 
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30      150         3 × 6    1.0 to 4.0                             
40      120         4 × 6    1.0 to 4.0                             
50      110         5 × 6    1.0 to 3.5                             
75      100         6 × 7    1.0 to 3.0                             
100     90          7 × 7    1.0 to 3.0                             
125     85          8 × 7    1.0 to 2.5                             
150     80          9 × 8    1.0 to 2.5                             
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     Illustrative of the plastic resins that are suitable for incorporation in the plaster or mortar coating placed on the hard-foam slabs or plates are methyl cellulose, homopolymers and copolymers of acrylic acid and methacrylic acid, e.g. styrol acrylates, and vinyl acetates. Such resins are used in a form in which they are dispersed in water. They are used individually or in any combination. 
     Plaster or mortar containing such synthetic resins in amounts of less than three percent by weight have a water-vapor-diffusion-resistance factor (μ) within the range of about 15-25, whereas a higher percentage of these resins or the same percentage of other resins can result in corresponding factors in the range of from 100 to 500. 
     This does not mean that such other resins are precluded from use in this invention. The noted difficulty is overcome, e.g., by incorporating foamed mineral particles, e.g. perlite (foamed volcanic glass), in the plaster or mortar. Such incorporating results in decreasing the water-vapor-diffusion-resistance factor. 
     The &#34;clamping&#34; effect between plaster or mortar and slab or plate is that which insures a mutual hold. The plaster has to hold the slab, overcoming the stresses created by residual shrinkage. On the other hand, the slab has to provide a good hold for the plaster. When the residual shrinkage exceeds a certain threshold amount, the slab can be destroyed. However, without shrinkage, no &#34;clamping&#34; effect is achieved. By selecting slabs or plates with a low residual shrinkage, it is possible to use those with a low specific weight which are considerably cheaper. Such slabs or plates also have increased thermal insulating properties, but this increase is insignificant. 
     The composition of plaster (in weight percent of typical ingredients) for application to the outside of the slabs or plates is: 
     
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               Example   Range                                            
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Cement           12           5 to 20                                     
Sand             73          70 to 90                                     
Chalk            0.7          0 to 10                                     
Preserving agents                                                         
                 0.01        0 to 1                                       
Methyl cellulose 0.2         0 to 1                                       
Polyvinylpro-                                                             
pionate          2.2         0 to 3                                       
Water added to   100         100                                          
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     The foam-plastic, e.g. polystyrene, thermal insulation slabs or plates 1 are adapted for application to outer walls of buildings. They have a residual shrinkage capacity of from 1.0 to 4.0 millimeters per meter, a finite thickness and two major surfaces, one of which (2) is substantially planar and the other of which (3) has rim portions 4 and 5 and plural grooves 6 of measurable and substantially uniform width and depth. The ratio of slab thickness (in millimeters) to the product of groove width (in millimeters) and groove depth (in millimeters) is between 5:3 and 9:4, or advantageously between 5:3 and 2:1. The number of grooves per square meter is from 5 to 15 more than the slab thickness in centimeters. 
     The groove cross-section is in quadrilateral form, e.g. rectangular or dove-tail in shape. The ratio of lengths of adjacent groove sides is between 2:1 and 1:1, and the grooves are preferably closer together near the slab or plate rim than they are in the center. 
     Outer building walls, such as masonry walls, are insulated by adhering the slabs to the outside of the wall in such close juxtaposition that the walls are covered, the substantially planar side of each slab facing the walls. The grooved sides of the covering slabs are then plastered with a mineral plaster advantageously having a synthetic-resin-component content of less than 2.5 percent by weight and a water-vapor-diffusion-resistance factor of less than 50 and preferably within the range of about 15 to 25. 
     INDUSTRIAL APPLICABILITY 
     This invention makes it possible to insulate, e.g., masonry walls, in a manner which minimizes on-site operations and maximizes the sturdiness and lasting qualities of the provided insulation. Advantage is taken of the shrinkage properties of freshly-prepared hard-foam plastic in producing an integral reinforced insulation. 
     The invention and its advantages are readily understood from the preceding description. The several components, the process and the obtained product are subject to various changes without departing from the spirit and scope of the invention or sacrificing its material advantages. The components, the process and the products described herein are merely illustrative of preferred embodiments of the invention.