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Hardwood Floors...All that they're cracked up to be
Well, 'tis the season... the season for cracks in your hardwood flooring. When the temperature drops, the heat goes on and the humidity goes bye bye, that's when the phone calls start coming in: "This floor is brand new, why am I getting cracks?" "Can you send someone from the factory out? I have gaps everywhere." The calls will continue until the heat goes off and the humidity returns.
Let me reassure you that not only are gaps common at this time of year, but they are almost welcome. If you have a tight floor now, there is a good chance you will have compression this summer, and that's a bigger trouble. It has been said that there in New England that we have two seasons, July and Winter or in wood terms, heating and non-heating seasons. There are several other reasons for cracks in floors that have little to do with moisture, here are a few: Foundation settlement, over a forced air heating ducts, and improper sub floor materials. The truth of the matter is that conditions vary greatly from site to site, but for certain, the heating months bring about the most significant changes in wood flooring and here's why as taken from the NWFA technical manual:
"Wood is a hygroscopic material. When exposed to air, it will dry or pick up moisture until it is in equilibrium with the humidity and temperature of the air in its environment. Absorption of moisture causes wood to swell. Loss of moisture causes wood to shrink. Shrinkage begins at 25-30% moisture content, the fiber saturation point. Shrinkage continues to 0% moisture content, an oven-dry state. Swelling occurs as wood gains moisture. Swelling occurs from 0% to 25-30% moisture content, the wood saturation point. Wood does not shrink or swell equally in all directions. Wood changes approximately: 0.1% along the grain and annular rings (radially) quarter sawn, and 5% to 15% across the grain parallel to the annular rings (tangentially) plan sawn."., Knowing that the majority of flooring used is plain sawn, you can see why we have so much gapping here in New England.
"If a 31/4" x 21/4" oak strip is exposed to an environment which changes the moisture content by 4% (i.e. from 7% to 11 %) the strip may swell as much as 1/32 of an inch. The opposite is true, if a 21/4" strip begins at 11% moisture content and loses moisture to 7% moisture content, the strip may shrink as much as 1/32".
Moisture changes such as those here in New England can range upwards of 9%, a change as drastic as this could cause strip flooring to lose a full 1/16". As humid as it was this summer, you can understand why gapping this heating season will be nearly unavoidable without some form of humidification system. The NWFA Technical Manual offers a more in-depth study of moisture relative to wood flooring including some helpful chart, scales and diagrams and is available through the National Wood Flooring Association.
Hardwood Flooring and Radiant Heat
Radiant heat is heat energy that is transferred from one surface to another through a space by means of energy waves. Radiant heat differs from other conventional heat systems which typically rely on rising warm air to heat surrounding air. Radiant heat is "omni directional." When there is a temperature difference between two or more surfaces, the heat energy will travel in multi directions from the warmer surface to the cooler until all surfaces have reached equal temperatures.
Because of radiant heat's efficiency and benefits (no dust, moderation of temperature), it has become more popular each year. In fact, manufacturers of tubing used in radiant floor heating systems increased production nearly 25% in 1997 over 1996.
Also, hardwood flooring has increased in demand and design over the last several years. Today, consumers surrounded by computers, fax machines, cell phones, pagers and synthetics of every kind still prefer natural products, like hardwood flooring, where technology and the forest collide.
Is solid hardwood flooring compatible with radiant heat systems? It is important to note that hardwood flooring does not impair radiant heat efficiency; however technical difficulties with the flooring may arise when using ¾ inch solid material. Wood is hydroscopic - it expands and contracts in size with an increase or decrease, respectively, of the environment's moisture content. Simply, wood functions like a sponge, Because of this, the use of humidity controls and acclimating wood products is critical. When wood experiences drastic shifts in moisture content, such as flooding, or conversely overheating, the wood fibers can become traumatized resulting in problems like cupping, warping, splitting checking and crowning. Prior to any installation, acclimation of wood products is key.
Radiant heat systems should be operated at least 48 hours prior to delivery of wood flooring. This allows time to drive existing moisture from the slab or sub floor. Upon delivery, wood flooring should acclimate to the site for at least 72 hours and all heat sources should remain operable throughout installation and finishing, should the floor need to be jobsite finished.
It should be stressed that cementations products such as concrete and gypcrete should be dried for a period of 50 days to 60 days before the introduction of any wood flooring product. The radiant hear boiler should not exceed 125 degrees, which should limit the temperature of the sub floor surface to about 85 degrees. This is important because it not only reduces he likelihood if overstressing the wood fibers, but also is the breakdown temperature for most mastics used with glue down flooring. In all cases the manufacturers' instructions and recommendations for the installation of their products should be followed.
Manufacturers of radiant heat systems and hardwood flooring often recommend the use of three thermostats, one to control the temperature of the water in the tubing, one to control room temperature per zone and one for outside the home. The thermostat outside the home allows the internal system to prepare for the arrival of colder weather. Many consumers move from the non heating season to the heating season with a bang. Cranking the heat up on the first cold day of the year can traumatize wood flooring. It's best in any case to bring heat on slowly over the course of a few days. Again, the use of humidity controls is always advantageous.
A variety of wood species are available today, and not all are suitable for installation over radiant heat. Each species has its own ability to change with moisture conditions; a change measured with the use of dimensional change coefficients. Such data is detailed in technical manuals and materials from organizations such as the National Wood Flooring Association. According to the NWFA, Douglas Fir, for example, has a change coefficient of .00267 and is approximately 28% more stable than red oak, which has a change coefficient of .00369. By multiplying the change in moisture content by the change coefficient, then multiplying the width of the board, the amount the wood will shrink or swell can be calculated.
Click here for a graph
Example: A three inch Teak board (change coefficient .00186) experiences a 3% change in moisture. Calculation: 3 * .00186 .00558 * 3 = .01674 inches.
This is a little technical for wood flooring, but very helpful when planning which products to use with radiant heat. Aside from the species, wood products that have been quarter sawn rather than plain sawn, offer more dimensional stability as well. When choosing which species of wood to install over radiant heat, doing your homework is critical.
Field Expansion...An application for experts
The Boston area is known throughout the country as being the exception to the rule in the wood flooring trade. It seems that for every tip and technique used elsewhere that we always find a way to do things a little different. This is what makes our region unique from other wood floor markets, and why many of the applications studies for new products involve special attention to the variety of needs here in New England. We are a valuable, diverse, pioneering and enthusiastic asset to our industry. However, whether you are a third generation floor man, sand and finish expert, installation genius, hardwood junky, pre-finished powerhouse, designer, architect, retailer, homeowner, mailman, chicken rancher bush pilot, WHATEVER... if you still 'net-fitting' wood flooring, you're not offering a professional wood floor installation.
When a wood floor is scribed to the baseboard, one of two things happen: the floor will shrink, thus leaving a neatly scribed gap everywhere just beg enough to catch dirt, dust-bunnies, kids toys, and other assorted aesthetic distractions. Or, secondly, compression-set, cupping, squeaks, cracked jams, etc., etc., etc. from the expansion of flooring into areas where THERE IS NO EXPANSION SPACE!
I have heard it all from the `I've been doing floors since Moby Dick was a minnow' speech, to the `Well, you don't scribe because you just don't know how to do it, nah, nah, nu, nah, nah.' speech. I have also had the occasions where the speech-givers have called me to say they need to be bailed out of a jam where the customer is complaining of a variety of problems, and in confidence all I can tell the floor guy is that he should have left proper expansion.
I know that many times, leaving 3/4" expansion is impossible, especially when the base is only1/2". However, make it a point to leave all that you can. I know floor experts that will clinch jobs because even though the guy before him does good work, he was the only one that promised to leave expansion- a guideline set by all major governing bodies of the flooring industry. Being 'in the business for forty years' isn't any justification for 'net fitting'. If this is one's gospel, then let them attend the next NWFA convention and they can tell that story to the hundreds of true wood experts that have more experience, knowledge, success and square-footage under their belts than most would hope to have. .
Here are some guidelines for the application of expansion are and keep in mind that this includes: Unfinished, prefinished, floaters, glue-downs, tracks, clips, and especially products like Natural Reflections and wide planking, which are sensitive to change.
· Heat and air conditioning should be operating ahead of installation.
· Products should be acclimated a minimum of 72 hours on the jobsite with boxes open for proper air circulation.
· Use a moisture meter to make sure flooring moisture content is equal to moisture content of the jobsite.
· Leave maximum amount of expansion possible, even if you have to cut the drywall.
Expansion is more important tangentially, or across the grain of plain sawn lumber which is most commonly used. Though wood expands only 0.1 % along the grain, longitudinally, remember that many floor squeaks come from wood rubbing against drywall and trim.
Since moisture content in New England runs an average 6-12%, at an average temperature of 50.5 degrees Fahrenheit, relative humidity at around 55%, a floor that is equal in moisture to the jobsite at close to 9% would be an excellent median point for installation. With proper expansion, this floor is less likely to gap or compress.
For low humidity jobsites that will eventually become humid, use one of the following methods to avoid problems, or make a note not to install the floor super-tight, leaving natural gaps alone.
· Use a .020" sheet metal spacer every 5 to 6 rows to leave small gaps
· Use a .010" spacer every 3 rows
· Use 'minute' spacers (.003") between each row. With Natural Reflections this can be accomplished by leaving the boards finger tight.
Note: if homeowners go on vacation, the humidity level inside the home will equalize with the outside ambient humidity. To avoid expansion, temperature should be maintained at approximately 70 degrees Fahrenheit.
Wood changes approximately 5%-15% across the grain and parallel to the annular rings (tangentially) in Plain Sawn wood: the greatest possible dimensional change. Because of this, in an area that could change as much as 4% (i.e. from 7% to 11%) wood could shrink or swell as much as 1/32". Also, note that finish coatings retard, but don't prevent moisture. Being adept to change in any trade is important. Most floor people don't use the recommended wood flooring applications, not because their way is better, but because that is their way and they do not want to try anything new. In actuality, leaving expansion is not only the professionally recommended method, but it will make a job go faster, neater but also reduces the risk of possible problems so as to guarantee repeat business. Door jams can be undercut which is neater and faster than scribing and no warranties are voided.
In closing, how one chooses to perform their particular trade is their business, but there is an understanding among the best and the majority in the wood flooring industry that expansion is a necessity, not an accessory. Good luck!
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