Decorative Concrete Goes DownstairsAdd the “wow” factor with a dressed-up basement.

Decorative Concrete Goes DownstairsAdd the 'wow' factor with a dressed-up basement.

The basement is no longer a place to store Aunt Ida's old furniture. No longer the default storage level, the basement accommodates a variety of lifestyles: an entertainment area with a pool table and bar, a playroom for young children, an office space, a home theater, or an in-law suite. Homeowners are more educated about options and ask how treatments can be applied to the floors and walls, or inquire about concrete countertop options. Contractors evaluate the dryness of the basement, check for the presence of water and mildew, and evaluate decorative options.

In addition, attitudes about basements vary in different parts of the United States. Where there is heavy bentonite clay soil that expands and holds water, builders are reluctant to install basements; while in cold climates, an in-ground living space might seem unattractive. With milder climates, the basement converts easily to a living space with windows and walkout areas.

Controlling Water Vapor Transmission

Basements nearly always have water issues and taking the steps necessary to handle those issues is more than half the work of a basement decorative application. Moisture vapor transmission (MVT) is the migration of water vapor through on-grade concrete or its cracks. MVT can cause the breakdown of the bond between a concrete topping and a slab or the discoloration of the concrete floor surface.

Above: This home adds light to the lower level with a curved wall using the removable concrete forming wall system. The poured-in-place steel-reinforced concrete staircase and the support columns are finished with an ivory-colored plaster coat. The mix is masonry cement and sand with polymer additives. The sand-to-cement ratio creates a suede-like texture. The concrete floor has chemical stain to finish. Photo: Mike Hancock

Consider the site's water table when determining the type of waterproofing membrane to install beneath basement slabs. 'The sand and gravel base material under a house drains away water but it also attracts and holds water molecules,' says Mike Hancock, concrete homebuilder and engineer for Oklahoma City's Basement Contractors. 'Most engineers specify 6-mil polyethylene, but that can break down over time.' A membrane can be damaged during construction by poking holes through it during rebar placement, and by rough base course material. There also can be leaks from sloppy sealing of sewer and drain penetrations through the membrane. 'It's not the thickness of the plastic that's important, but the composition of the plastic that affects strength, longevity, and permeance,' says Paul Miller, Stego Industries. Miller recommends 10 or 15 mil polyolefin membranes for long life, low permeance, and puncture resistance.

Once concrete is installed, there are formal and informal ways to check the moisture vapor emissions rate (MVER). A calcium chloride test will yield a result in pounds of water vapor per 1000 square feet in 24 hours. You're hoping it indicates that the MVER is under the typical maximum of 3. Sometimes contractors conduct an informal test by taping a 1-foot square clear piece of plastic onto a basement floor for 24 hours. If the plastic shows condensed moisture, a more extensive evaluation should be conducted.

There are products available that can reduce the MVER. Some manufacturers have products to apply over the top of a concrete slab to minimize MVT prior to installation of an underlayment or a wear surface topping.

Heating and Cooling Requirements Differs

When designing basement heating and cooling systems insulation is an important consideration. 'In a cold climate without an insulating barrier, the heat migrates below into the ground,' says Kevin Percy, owner, Percy Concrete and Design, Wrentham, Mass. 'A 4-inch-thick concrete floor needs two inches of foam insulation below it with all seams taped.' The heating and cooling design should provide year-round comfortable living-temperature and humidity, breathable air quality, and mold and fungus prevention.

Condition the Environment

Dark, dank, and dismal are traditional words associated with basements. In addition to heating and cooling the basement, a fireplace, radiant heat, and more light make the basement more enjoyable. More people are installing radiant heat in basement slabs. They may ask for a hot water system that runs hot water through pipes in the floor or an electric system that uses mats. With either system, carpet isn't needed; just apply a decorative concrete treatment instead. 'Create more light by digging deep window wells or consider wrapping windows around basement wall corners to increase natural light. This is especially important if the basement lacks a walk-out,' says Hancock, who also engineers basement concrete fireplaces.