Impact sound which is the result of walking, dancing, dropping objects, etc., is defined as Impact Insulation Class (IIC). These are usually in the lower sound frequencies.
The second class, though there are more, is classified as Sound Transmission Class (STC). This class refers to airborne sound. These transmissions are in a higher group of frequencies. They are generated by radios, televisions and ordinary conversation, as well as other airborne sounds.
Both sound classes are rated in decibels. For purposes of this article, our concern is the IIC because we are concerned with flooring. The most difficult sound class to reduce is the Impact Insulation Class.
In many cases, an attempt to reduce IIC is made by introducing a plenum and a gypsum board ceiling or acoustic tile fastened to what is called a resilient channel. Oftentimes, this system may not be able to sufficiently reduce the decibel levels.
This is where the aforementioned products now being marketed come into play. These products come in the form of cork, polyethylene, fiber mats, rubber, and so on. These would be the products used under floor coverings such as ceramic and wood, and even vinyl. They help reduce the IIC levels -- sometimes to permissible levels and sometimes not.
A few noise-reduction products do not necessarily require a plenum and acoustical tile installation on the ceiling beneath the floor. Custom Building Products and Neutra-Phone are two firms that I know for certain manufacture alternative sound-reduction systems. No doubt there are more. Neutra-Phone's, when installed on concrete, requires an 11-inch-thick slab.
Recycled rubber from tires is appearing more frequently in sound-abatement situations. Custom Building Products, Neutra-Phone and Dodge Regupol-QT are a few who supply such products. Rubber is an effective sound barrier, as is cork.
Kinetics of Dublin, Ohio, markets a 5/16-inch (8mm) product with pre-compressed molded glass fibers stiff enough to prevent grout in tile floors from cracking.
It is interesting to note that Amorim Industrial Solutions is now marketing two new products in their acoustic Cork Products line. The first is a two-layer cork product with coconut husks in between to provide extra flexibility. The total thickness is 1/2-inch with an IIC rating of 55+.
The second Amorim product is called Acousti Cork Vapor Bloc. The product is 6mm thick. The cork is coated on two sides and the company notes that 100 percent solids urethane adhesive must be used to bond the cork to the substrate and also to bond the flooring to the cork. In their experience, water-based adhesives do not provide an adequate bond. This product is designed for use with thin (1/2 inch or less) solid-wood flooring.
Another cork sound- and crack-isolation membrane is manufactured by Bostik Findley. Their field testing with their 1/4-inch (6mm) cork with suspended ceiling had ratings well in excess of the required ICC value of 50. It is interesting to note that, in their specifications relating to flammability, their product is considered fire retardant and does not produce toxic emissions during combustion.
MAPEI's membrane falls into the sheet category. It is a flexible reinforced, thin, peel-and-stick membrane.
I also should mention that many of the poured-gypsum underlayment companies, such as Hacker Industries, place a mat beneath the underlayment rather than on top.
Right now, ASTM is seeking participation in an ongoing evaluation to extend the sound testing on concrete slabs to sound impact on joist floors with wood subfloors. This will allow designers to select among floor coverings, free of any contribution from the supporting floor.
Anyone willing to participate should contact the task group chairman at ASTM.
