15 December

Guidelines for moisture content on common substrates

Excessive moisture in CMU, concrete, exterior gypsum sheathing, and wood-based sheathings can cause premature damage and adversely affect the long-term performance of the building envelope.

Both waterproofing and air and vapor barrier installers are asked regularly to apply products over questionable substrates. They, in turn, ask manufacturers what acceptable moisture content levels are for certain substrates. Carlisle Coatings & Waterproofing offers these general guidelines:

  • Wood based sheathings (plywood, OSB) shall be at a moisture content of 19 percent or less. Some experts require a moisture content of 16 percent or less.
  • Exterior gypsum sheathing shall be at a moisture content of one percent or less.
  • Accepted ranges for concrete and CMU are not specifically provided and specifications typically only require that the surface be dry. A good rule of thumb, however, for concrete and CMU is a moisture content of less than five percent for fluid applied air and vapor barriers and 12 percent or less for self-adhered air and vapor barrier membranes.

Design professionals and substrate manufacturers should always be consulted for establishing the level of acceptable moisture content in the substrate. Further, relevant ASTM standards should be reviewed to verify the criteria are at appropriate levels for in-service performance. ASTM D4263-83 is the standard for testing moisture in walls, while five ASTM test methods are used to measure moisture in floors (ASTM F1869-11, ASTM F2170-11, ASTM F2420-05 and ASTM F2659-10).

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