Q&A / 

Underlayment for Floors

DEAR TIM: In the very near future, I will be installing lots of new and different flooring materials in my home. Can I just remove the carpeting and install my flooring material over the existing subfloor or do I need to install an underlayment? Since I want my new floors to look as good as possible, what is the best thing to do? I am very concerned about the kitchen and bathroom areas since water seems to find its way through and under any finished flooring material. Jennifer M., Atlanta, GA

DEAR JENNIFER: You are very wise to think before you act with respect to all of your new flooring. It is my guess that the total cost of the new flooring will be substantial and the last thing you want is for it to fail or fail prematurely because it was installed improperly. Finished flooring, even carpeting, needs a solid foundation for it to perform well over time. All too often some builders and remodelers as well as poorly trained installers overlook the importance of floor underlayments. Most flooring failures or problems are traced to inadequate or poorly installed flooring underlayments.

For many years, wood based products have dominated the flooring underlayment industry. Plywood, oriented strand board, sawdust composites, cement board, etc. are widely available and are commonly the material used in both new home construction and remodeling jobs. The wood based underlayments can warp and swell when exposed to moisture. This can cause the finished flooring to buckle and fail even if the underlayment relaxes after it dries out.

Many consumers and tradespeople, unfortunately, assume lots of things about finished flooring such as ceramic tile, hardwood, laminate flooring, cork, sheet vinyl, vinyl tile, etc. They feel that if the sub-floor or underlayment looks and feels substantial then it is fine to proceed with the finished flooring. The truth of the matter is that it is far more complicated. Many finished flooring products have specific recommendations with respect to the type of material the finished flooring is placed upon. Even adhesive manufacturers are sensitive to the type of underlayment being used. For example, an adhesive may work well with the vinyl or ceramic tile, but who cares about that if it bonds poorly to the underlayment?

A new underlayment product has recently hit the marketplace that is very attractive to a wide bandwidth of the flooring industry. This product is a gypsum fiber panel that has many positive qualities. It is smooth, has superior water resistance, has higher impact resistance than traditional wood based products, can be cut with a utility razor knife, is made with 95 percent recycled materials and is competitively priced.

Keep in mind that many traditional wood based underlayments contain resins, adhesives, solvents or dyes that can sometimes seep through and into the finished flooring material. If this happens, your finished flooring can be ruined. The new gypsum fiber underlayment does not contain any of these problematic ingredients.

The new gypsum fiber product is available in two thicknesses: 1/4 and 3/8 inch. This variety allows you to create flush finish floor transitions when you change from one material to another. There is no reason why an angled transition threshold has to be used if you are installing finished flooring materials that are different thicknesses.

Many flooring problems happen in houses that are built over crawl spaces. All too often an underlayment will buckle or warp because of water vapor that escapes from the soil beneath the crawl space and then permeates the subfloor and underlayment. If you have a crawl space, be sure you cover the soil with a high performance vapor barrier before you install any underlayment or finished flooring material.

It is also very important to make sure that existing wood subfloors are dry before you install an underlayment. The moisture content of a wood subfloor should not exceed 15 percent. Use a moisture meter to test for moisture content. Be sure that the fasteners used to install the underlayment are driven correctly. The top of the fastener should be flush with the top of the underlayment or slightly below the surface. Above all, make sure that you are using an approved underlayment. Get written specifications from the finished flooring manufacturer and choose a product that is on the list.

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One Response to Underlayment for Floors

  1. Have house built in 1963 with diagonal layed subfloor. Replace old hardwood with new. It has been suggested that to get rid of squeaking floor, remove old floor, underlay with 1/2" plywood, glued and screwed, felt paper, then new floor.

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