Masonry Magazine August 1988 Page. 22
TABLE 2 (Continued)
Permeance and Permeability of Materials to Water Vapor
# Liquid-Applied Coating Materials!
Commercial Latex Paints (Dry Film Thickness)
| Materials | Thickness (In.) | Resistance (Rep) |
| ------------------------------ | --------------- | ---------------- |
| Vapor Retarder Paint | 0.0031 | 2.22 |
| Primer Sealer | 0.0012 | 0.16 |
| Vinyl Acetate/Acrylic Primer | 0.002 | 0.13 |
| Vinyl-Acrylic Primer | 0.0016 | 0.12 |
| Semi-Gloss Vinyl-Acrylic Enamel| 0.0024 | 0.15 |
| Exterior Acrylic House and Trim| 0.0017 | 0.18 |
Paint 2 Coats
| Materials | Resistance (Rep) |
| ---------------------- | ---------------- |
| Asphalt Paint on Plywood | 2.5 |
| Aluminum Varnish on Wood | 3.3-2.0 |
| Enamels on Smooth Plaster| 2.0-0.66 |
| Primers and Sealers on Interior Insulation Board | 1.1-0.480 |
| Various Primers Plus 1 Coat Flat Oil Paint on Plaster | 0.63-0.330 |
| Flat Paint on Interior Insulation Board | 0.25 |
| Water Emulsion on Interior Insulation Board | 0.03-0.0120 |
| Materials | Oz/Ft2 | Resistance (Rep) |
| --------------------------------------- | ------ | ---------------- |
| Paint- 3 Coats | | |
| Exterior Paint, White Lead and Oil on Wood Siding | | 3.3-1.0 |
| Exterior Paint, White Lead Oxide and Oil on Wood | | 1.1 |
| Styrene-Butadiene Latex Coating | 2 | 0.09 |
| Polyvinyl Acetate Latex Coating | 4 | 0.18 |
| Chioro-Sulfonated Polyethelene Mastic | 3.5 | 0.59 |
In this chapter the permeance, resistance, permeability and resistance per unit thickness values are given in the following units:
Permeance Perm -gr/h.ft.in.Hg
Resistance Rep -in.Hg.fh/gr
Permeability Perm.in. grih.ft.in.Hg/in.)
Resistance/Unit Thickness Rep/in. (in.Hg.ft.higr)/in.
Table 2 gives the water vapor transmission rates of some representative materials. The data are provided to permit comparisons of materials; but in the selection of vapor retarder materials, exact values for permeance or permeability should be obtained from the manufacturer of the materials under consideration or secured as a result of laboratory tests. A range of values shown in the table indicates variations among mean values for materials that are similar but of different density, orientation, lot or source. The values are intended for design guidance and should not be used as design or specification data. The compilation is from a number of sources; values from dry-cup and wet-cup methods were usually obtained from investigations using ASTM E96 and C355; values shown under others were obtained from investigations using such techniques as two-temperature, special cell, and air-velocity. Values included were obtained from Ref. 14 to 29 and other sources. Some values were obtained from unpublished tests conducted by Pennsylvania State University and the Building Research Div., National Research Council of Canada.
Depending on construction and direction of vapor flow.
Usually installed as vapor retarders, although sometimes used as exterior finish and elsewhere near cold side where special considerations are then required for warm side barrier effectiveness.
Dry-cup method.
Wet-cup method.
Other than dry- or wet-cup method.
Low permeance sheets used as vapor retarders. High permeance used elsewhere in construction.
Basic weight in Ib per 100 ft² (Ib per square ft)
Resistance and resistance/in, values have been calculated as the reciprocal of the permeance and permeability values.
Cast at 10 mils wet film thickness. 31
*From ASHRAE Handbook of Fundamentals.