An occasionally heard comment about ceramic tile floors, especially those on suspended floors over living areas, is “I would really like tile but it’s so noisy.” It can’t be denied sounds can be more readily heard with the installation of any hard surface flooring. Many building codes require sound attenuation when tile is used in an apartment or condo setting. Thus, with the increased awareness and availability of sound control products coupled with the increasing enforcement of code requirements, it should come as no surprise they are a fast-growing segment of products in the ceramic tile market. Manufactures have also taken note, and as a result, we see an increase of products from non-traditional supply sources. Some work well with ceramic tile, others don’t. Those that work with the more popular types of stone are even fewer. Let’s look at a few of the basics in noise suppression starting by defining sound control.
There are two types of ratings used in sound control. The term Sound Transmission Class (STC) refers to the evaluation used to quantify the transmission of airborne sound through building elements, such as walls or floor systems. This type of sound is typically voices, radio, or television. STC can be measured under standards published by the American Society for Testing of Materials (ASTM) Standard C634 and is tested using ASTM Test Methods E90, E336, and E596. These values are then stated as an exact number to the right of the initials STC such as STC 35 found in the product literature. Field testing is also commonly done using ASTM Method E336 which provides an accurate expectation of performance in the actual setting of the structure. When field tests are performed, those values are designated by the initials FSTC to the left of the numeric value such as FSTC 35.
The term Impact Insulation Class (IIC) refers to the measurement standards used to quantify the transmission of impact sound energy passing through a floor or ceiling assembly system. These types of sounds would be the equivalent of foot traffic, dropped articles, or furniture moving in an adjoining living area. This can be measured under ASTM test numbers C634, E989 and E492.
A newer test for concrete subfloors has also been recently approved, ASTM E2179-03E. As with STC, values are stated as an exact number to the right of the initials IIC. Field testing can also be done using ASTM Method E1007; once again field test values are designated by the initial F and read FIIC. To assure accurate representation of the listed values, testing should always be done by an independent certified laboratory.
Products that have only Field Test reports (FIIC) and no laboratory testing should be considered with caution. Field tests are project specific. Comparing different field tests done in buildings other than your own or those identically constructed is not an accurate way to make a proper assessment of product performance. Many materials that are promoted for sound control in hard surface flooring may not be suitable for direct bonding in tile and stone installations. Often they are too compressible and do not provide proper support for tile installations. In some cases it maybe necessary to use additional reinforcing materials, such as mortar beds, poured in place overlays, backer boards, epoxy mortars and grouts, thicker or larger tiles, or other methods to provide a structurally sound installation. It is recommended that all product systems used for sound control be subjected to an ASTM C627 rating; commonly referred to as the Robinson Floor Test and such products/systems meet a minimum “Residential Rating.” All components of the test assembly should be divulged to determine that the product in question is able to achieve the performance rating desired, for a given installation.
Make sure the data of whatever product you’re considering lists the values for your type of building construction. Concrete slabs come in a variety of thicknesses and compositions (e.g., hollow core, post-tensioned, pre-stressed). The most commonly cited are 6” and 8” concrete slabs with or without a suspended ceiling assembly. Test results for these two thicknesses vary when comparing field tests versus laboratory tests. The field tests typically result in a much higher range of values than those conducted in the labs.
Wood frame construction is a little easier to deal with as it will normally have a gypsum wallboard ceiling assembly. To achieve a better environment for sound control, the use of resilient metal channels supporting the gypsum wallboard and sound-absorbing insulating batts in the cavity is recommended. An assembly of this nature with a single layer subfloor has an approximate IIC rating of 45 all by itself. Adhering a tile or stone surface will actually lower the IIC to around 40. The reason for this is that the hard surface increases noise levels at the higher frequencies, thereby reducing the overall IIC rating. If the sub-floor thickness is doubled and the ceiling wallboard panels are doubled as well, the net effect will increase both the STC and IIC rating.
Effective sound reduction, while easily achieved in most instances, requires a degree of knowledge and diligent adherence to the specific product manufacturer’s recommendations. When STC and IIC values are provided by a manufacturer they typically come as a result of a very specific assembly. Also as previously mentioned, it would not be wise to install an overly compressive sound reduction material under ceramic tile unless the product has been performance tested using ASTM C-627, the Robinson Floor Test.
You should also inquire if there is any tile size, setting material, or specific grout recommendations. Many sound products have specific limitations on either tile products that can be used over their membranes or materials used for bonding and grouting. I would approach the use of any stone flooring product over a sound reduction membrane with extreme caution as very few products are capable of providing adequate support for stone products.