I am using 8-inch, 3-core concrete blocks in the construction of residences and some stores. How can I avoid cold, damp walls (sweating walls)?
The damp walls are caused by condensation of moisture on the cold surfaces. Remember, concrete like stone is a relatively good conductor of heat, and in cool or cold, damp weather the walls will quickly cool. The inside of the building is warm and there is usually moisture in the air. Warm air can carry more moisture than cool air. As the warm air hits the cold wall surfaces, some moisture will condense on the block wall. To prevent this, the wall must be insulated to reduce the heat transfer, so that the inside surface is warm enough to stop condensation. The type and amount of insulation will vary with local conditions, but can be readily calculated. In general a coefficient of heat transmission of .25 to .30 BTU per hour per square foot per degree Fahrenheit will satisfy most conditions. An 8-inch, 3-core concrete block has a thermal conductivity of .58 BTU. A Haydite block has a thermal conductivity of .50 BTU, a slight improvement. Here is an example of insulation: 1/2-inch plaster on 3/4-inch furring and 1/2-inch rigid insulation will reduce the heat transmission factor to .22. The Portland Cement Association has published some excellent data on thermal insulation of concrete and concrete-block walls.