Here is a great Q&A regarding hardwood floors. In particular, it has a good description of hardwood applications over concrete floors. Enjoy!
Q&A on hardwood floors
Why choose hardwood flooring?
Wood adds beauty and warmth to any room.
Whether building a new home, adding on, or just taking up old carpeting, you should look at the wide variety of wood flooring available. Wood floors can last well over 100 years and are easy to maintain: just vacuum or dry mop at least once a week. Most spills can be easily wiped up without the worry of staining. When the surface finish wears, or gets scratched over time, you can sand and refinish the floors to make them new again.
For people with allergies, wood flooring is one of the best types of flooring to have. With carpeting, dust mites thrive and dirt and pollen build up in the carpet even with constant vacuuming and washing. Dust and pollen are simply cleaned away from a wood surface.
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With the many varieties of woods and colors of wood flooring, it's easy to find one that will fit most any design option you have. Some options to consider when choosing a wood floor are:
The style or look of the wood flooring widths of the boards, desired The type of wood The grade of the flooring. Also affecting your decision is what the wood flooring will be installed over and the type of subfloor in the room (i.e. plywood, tile or cement). Wood flooring is manufactured in four ways:
3/4" solid flooring (unfinished, or pre-finished) Engineered (unfinished, or pre-finished) Longstrip (pre-finished) Parquet (unfinished, or pre-finished) There are also a variety of specialty products to enhance your room, such as borders or feature strips in domestic or exotic woods, crests and medallions, and laser inlays and patterns. When installing new flooring in an addition or remodeled kitchen, you can try to match flooring from an adjoining room or have the new flooring a bit different from the rest of the house. When trying to match new flooring to existing flooring, a perfect match might be impossible, i.e. age, graining, colors, milling. It may be better to go with the same species but in a different width than the old flooring for an obviously different look.
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How do I choose a hardwood that is right for me?
Today there are many different species, styles and colors of hardwood flooring to choose from. Before choosing a hardwood floor, think of what type of look you are trying to achieve for the room. There are three basic types of looks: contemporary, formal and country.
For a more contemporary look, use a 2-1/4" or 3" wide floor boards in a clear, or select grade. This will give the room a more uniform color and a narrow line, modern look.
For a more formal, or dressy look, use a clear grade of 2-1/4 inch wide planks in the center of the room with a 12-inch wide perimeter or picture frame of the same wood parallel with the walls. A feature strip of a different wood species, either lighter or darker, installed around the edge of the center area would create a distinct elegant appearance.
For a more country feel, 4" to 8", or wider, planks would be appropriate. Hand forged antique cut nails can be installed for a colonial style. For country both light and darker colors are used.
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Another consideration is which color tones for a hardwood floor would compliment the window treatments, fabrics, and furnishings that exist in that living space. Also, remember that darker hardwood floors are generally used in formal, or traditional interiors, while lighter colors, especially in maple or oak, are used in country or contemporary type interiors. To achieve a darker hardwood floor you can install a darker species of wood or use a stain for the appropriate shade.
You should also realize that some species of wood will darken faster than others. American Cherry and Brazilian Cherry will darken from direct sunlight (ultraviolet light) and from age. To help slow down this darkening, the use of directional window blinds can be used to deflect the sunlight off the floors during the hours of high sunlight. This also helps keep the color in furniture, drapes, and rugs and other flooring wood species from bleaching out lighter in color.
The possibilities and design styles are endless. But remember flooring is an important focal point of any room.
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Will my wood floor dent?
Hardwood floors as with all wood are comprised of basically soft wood fibers and millions of cell structures. The density of these wood fibers technically makes one wood harder than another. But all wood will dent if something heavy is dropped on it. The spike end of a high heel shoe can indent the surface of the wood as well. (A 110-pound woman will exert 2,000 pounds of pressure at the tip of the heel.)
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There are three basic types of hardwood flooring installations: nail down, floating installation and glue down. The type of installation method used is really determined by the type of hardwood flooring, and the type of subfloor.
The 3/4" solid wood floors should only be nailed down, and are recommended only for above grade installations over a wood subfloor.
The engineered and longstrip flooring can be nailed, glued, or floated on all grade levels. Engineered floors are more dimensionally stable, and are an excellent choice for those who prefer hardwood flooring in a basement, family room, or playroom. Engineered floors can also be floated over the top of an existing vinyl, or ceramic tile floor, which can eliminate the cost of tear up.
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Unfinished or prefinished hardwood?
Unfinished flooring is installed as either strip, plank or parquet. A sanding and refinishing process is used after installation. Unfinished wood can be purchased as solid 3/4" thick or engineered (an assembly usually 5/8" or thinner made by bonding layers of lumber with adhesive with a top surface of veneer of a desired species, such as oak, maple, ash.)
Prefinished strip, plank or parquet floors are either factory finished or acrylic impregnated (liquid acrylic and stain are impregnated throughout the pores of the wood) when manufactured). Prefinished floors can be purchased as solid 3/4" thick wood or as an engineered wood. Prefinished flooring may have up to 10 coats of finish applied at the factory and have a 25 year wear warranty. Floating floors are engineered prefinished flooring in which the joint of each panel is glued to the neighboring panel. This enables the floor to move or float as a whole when the wood expands and contracts from the moisture content. When installing a floating floor, a foam pad is recommended as a moisture retarder and cushion.
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What is the best finish for a wood floor?
There are a variety of finishes used on hardwood flooring today. We have dedicated a whole page to this subject.
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The solid 3/4" flooring may be sanded up to approximately seven times before replacement is needed well over a hundred years. The engineered flooring can be sanded up to 3 times for a average life of approx. 30 years. Acrylic-impregnated flooring should be lightly sanded and polished.
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Are there different grades of hardwood flooring?
Yes, hardwood flooring comes in different grades. The grading is done by the appearance of the flooring boards. Different manufacturers may have their own names for the different grades, but most do follow the guidelines set by the National Oak Flooring Manufacturers Association (NOFMA). NOFMA has established rules governing their milling and grading of standard 2 1/4 strip oak flooring. Below are their descriptions. Mills producing hardwood flooring that are not members of NOFMA are under no guidelines.
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Unfinished Oak, which is the most widely used flooring material, has four basic grades. Three of which can be purchased as either Red Oak or White Oak.
Clear Plain, or Clear Quartered - This is the best grade and has the best appearance. It is the most uniform in color and has little or no defects. The lengths of the boards are longer, the average being 3-l/2 feet with the longest generally being 8 ft. a) Select Plain or Select quartered - This is less uniform in color than the clear grade, but has an excellent appearance. There may be some minor defects (pinholes, knots, flags) which adds character to the flooring. The lengths are shorter than the clear grade. The average board being around 3 feet some generally being 7 feet. b) Select & Better - A combination of Clear and Select grades. No. 1 Common - This flooring has a varied appearance with light and dark boards. The character marks such as knots, flags, pinholes and others are much more prevalent than on the select grade. The average lengths are very short around 2-1/2 feet long. No. 2 Common - This grade of flooring has a very rustic appearance. Bundles may contain Red Oak and White Oak mixed together. There is an abundance of character marks and other imperfections. The average length is around 2 feet. Back to top
Unfinished Hard Maple, Beech and Birch come in five different grades.
First grade - This has the best appearance. There are natural color variations and limited character marks. Second grade - This has a variegated appearance with good wood characteristics of the species. Second & Better grade - This grade is a combination of First and Second grades. Third grade - A serviceable grade with a rustic appearance. All wood characteristics of the species. Third and Better grade - This is a combination of First, Second and Third grades. Back to top
Generally any of the above flooring can be installed over a subfloor of plywood, or a solid 3/4" wood surface. If your subfloor is concrete or stone, your choices maybe limited. Excessive moisture that may be in concrete, or stone will be absorbed into the wood flooring installed on top of these surfaces. A solid 3/4" wood floor may buckle, and/or cup from the excess moisture. If a moisture reading of the concrete or stone is over 12% moisture content, a wood floor shouldn't be used until you determine the source of the moisture and correct it. If the moisture reading of the concrete is below 12%, the best choice of flooring in these instances would be either a floating floor with a foam pad or vapor retarder, or a glued-down engineered hardwood floor with a waterproof adhesive.
If a 3/4" solid wood floor is desired, a raised (1-1/2") system of sleepers 12 - 16 inches apart would have to be constructed with a plywood platform on top. It is critical prior to the construction of sleepers to put a vapor barrier of 4 -6 mil polyethylene plastic down with all joints taped with duct tape.
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How much wood do I need?
Most flooring is sold by the square foot. The square footage is the actual measurement of the area to be covered by flooring. A waste factor of 5% must be added to the amount of square footage of flooring needed to allow for cutting waste. Example: a 10' x 10' room = 100 sq. ft. 5% of 100 is 5 so you will have to purchase 105 sq. ft. in order to have enough flooring. The cutting waste also allows for some minor defects to be cut out.
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Before any flooring is delivered make sure that the conditions are right. All concrete, masonry work, plastering or anything else that deals with moisture must be thoroughly dry. Normal living conditions should be maintained 5 days before any flooring is delivered, i.e. heating, air conditioning.
When the flooring is delivered, store it in the rooms where it will be installed. This is so the flooring can acclimate to the conditions in which it will be installed. Average acclimation time is generally one to two weeks. A moisture reading should be taken of the flooring and subfloor before installation to ensure the levels of both are within the range of relative humidity for your area. (Generally between 6-12%.)
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Expansion and contraction
Hardwood flooring like all woods are considered "hydroscopic," which means that they have the ability through their cell structure to absorb and release ambient moisture that's prevalent in its environment. Hardwood flooring at the time of manufacturing is kiln dried from approximately 30% moisture content to between 6-12% moisture content. This figure of 6% to12% moisture content represents the standard normal relative humidity level of between 45% and 55% that normally should be present within your home. If that home's standard, normal relative humidity changes for any great length of time, a dimensional change may be seen in the size of each board.
For example: Flooring may shrink in size during the heating season when the ambient air in the home becomes dry. The flooring itself then dries out, losing moisture. This can cause gaps between the boards. The size of these seams will be large or small, depending on the amount of moisture loss. These gaps often close when the flooring regains its lost moisture content.
Flooring also can absorb more moisture and expand during the times of more rain and humidity. This sometimes causing cupping in the floor boards. Learn more about cupping here.
It can be controlled. If, during the dry heating season you notice your floor boards starting to contract in size leaving gaps between floor boards, introduce moisture into the area using a humidifier. Maintain the relative humidity at 45-55% year round. If you want, you can get a small digital moisture meter available at your local hardware center. It will tell you what you relative humidity is daily.
During the rainy season, the flooring might expands and starts to cup. A dehumidifier to remove excess moisture from the air, but it could mean a larger problem involving moisture under the floor of your home. Find out more about that here. Remember that maintaining this 45-55% RH year round is not only beneficial for your flooring its also good for your own health, and comfort.