With today’s fast-track building conditions, there are increased problems with underlayment joint show through (where underlayment telegraphs a 1/16” to 1/8″ vein-like hump) and sheet vinyl tunneling (de-bonded material approximately 1″ to 2″ directly over the underlayment joint).

Following are some of the causes and effects of these problems.

Highly efficient construction schedules often do not allow time to completely dissipate excess moisture retained during the building process. A tremendous amount of water is used during construction.

This water can be found in the following places:

Concrete foundations emit moisture at an approximate rate of 3 pints per cubic foot. Consider for example, the foundation wall in a small 20′x20′ basement. If the walls are 1′ thick, 8′ high and 20′ long on all four sides, roughly 1,920 pints (240 gallons) of moisture will be emitted from the foundation walls. And, if a coating has been applied to the exterior of the foundation walls, most of that moisture will migrate to the inside of the structure. Drying time of a 1′-thick foundation wall is approximately 1 year.

Concrete slabs are another major source of moisture. A 4″-thick concrete slab emits 1 quart of water per square foot. So in the same 20′x20′ square slab, 100 gallons of water will be emitted from the slab. Coupled with emissions from the foundation walls, there is a tremendous amount of moisture out of these concrete surfaces.

Today, lumber-built structures are no longer kiln-dried; they are “surface dried”. Depending on the species and region where the lumber was milled, the moisture content is 4% to 6% greater than normal. Because there are so many variables involved, it is impossible to accurately gauge moisture emission amounts. Easier to quantify is the amount of movement in the wood as it completely dries out. Some of the moisture migration from the concrete will be absorbed by the lumber, which increases its dimensions depending on the type of wood.