Let’s take a look at wood flooring and some of the characteristics and issues relative to this product; one of the fastest growing in popularity and use.
Solid Wood Flooring – Solid wood floors are one solid piece of wood and are generally 3/4″ thick. Solid Hardwood Floors are produced from the finest American and Canadian hardwoods including red & white oak, ash, American cherry, hickory and maple, and are available in several widths. There is also an increasing supply of solid wood floors from other parts of the world. Some of it, if you don’t know the supplier, can be risky using. Because solid hardwood floors are more susceptible to moisture than engineered wood floors they should only be installed above grade over approved wooden subfloors and must be nailed-down. Solid wood floors can generally be
Engineered Wood Floors – These floors are produced by laminating several hardwood plies together to form the planks. Most engineered floors can be glued-down, stapled-down or floated over a variety of subfloors including wood, dry concrete slabs and some types of existing flooring. Engineered hardwood floors have cross-ply construction which reduces the expansion/contraction of planks caused by variations in humidity and allows these floors to be installed anywhere in the home. Engineered Hardwood Floors come in a wide variety of widths, thicknesses and colors in both North American and Exotic hardwoods. One issue of concern with these floors is that of multiple layers of varying woods, between 5 and 7 plys. There can be an imbalance of moisture between the top board and the core board(s) which can create a Crook in the material. This would cause the material to lift or distort on the floor. There are ANSI standards for engineered wood that dictate tolerances of movement.
The floor that fit so well when it was first installed now shows cracks, cupping or buckling. Those are the most common changes that moisture can inflict on a floor. They do no favors for the customer, or for the hardwood flooring industry. Tales of how floors were damaged by water, for whatever reason–improper installation or careless maintenance by the owner–leave the impression that wood floors are more problematic than other flooring choices. For wood flooring professionals, it’s important to inform end users about the normal behavior of wood in relation to moisture. Most solid wood flooring will contract during periods of low humidity (usually during the heating season), sometimes leaving noticeable cracks between boards, or else expand during periods of high humidity. To help minimize these effects, users can stabilize the environment of the building through temperature and humidity control. This is an overview of how water and wood don’t mix-and what to do if they do. Spotting any potential moisture problems, and taking the proper steps to avoid them, is the path to the most-serviceable floor. Fortunately, many of the instances that involve moisture can be mitigated before, during or soon after installation. A well performing wood floor is often the result of an installer taking the proper time and care necessary for a successful installation. It involves knowledge of: the expected moisture content of wood flooring in a particular area after acclimation; the moisture content of flooring at the time of installation; and the expected “in use” changes. Moisture is a large part of the reason for how wood behaves, both during the machining process and after installation. Installers would do well to understand moisture’s effect on wood in some detail.
Water and Wood Basics – The easy explanation that students learn in grade school – trees grow with roots in the ground and leaves in the air – still serves as the basis for understanding the never-ending relationship between water and wood. The roots collect moisture and nutrients from the soil and ship them through vessels or fibers up the trunk and branches to the leaves. These vessels are similar to the “strings” in a stalk of celery. They are similar, too, to a group of soda straws gathered together, running up and down the tree. That’s the simple version of how a still-standing tree is made up of vertically-aligned fibers. Cut the tree down, and the fibers are horizontal. Saw it and manufacture strip flooring, nail the floor down and most of the fibers are still horizontal, running the length of the boards. In the live tree, the fibers are loaded with moisture, as sap. After being cut, the tree begins to dry out, just like a rose will wilt after it’s picked. As the tree’s fibers dry, they shrink in thickness or diameter, but almost none lengthwise. This shrinkage, characteristic of all woods, is critical in understanding the effect of moisture on wood flooring. You must remember that wood flooring material is still a tree but in a different form now and it is still subject to the same reaction it was when it was a standing tree.
Moisture content in solid wood is defined as the weight of water in wood expressed as a percentage of the weight of oven-dry wood. Weight, shrinkage, strength and other properties depend on the moisture content of wood. In trees, moisture content may be as much as 200 percent of the weight of wood substance. After harvesting and miring, the wood will be dried to the proper moisture content for its end use. Wood fibers are dimensionally stable when the moisture content is above the fiber saturation point (usually about 30 percent moisture content). Below that, wood changes dimension when it gains or loses moisture. Here are some quick points about shrinking and swelling: Shrinkage usually begins at 25 to 30 percent moisture content, the fiber saturation point. Shrinkage continues to zero percent moisture content, an oven-dry state. Swelling occurs as wood gains moisture, when it moves from zero to 25 to 30 percent moisture content, the fiber saturation point. Different woods exhibit different moisture stability factors, but they always shrink and swell the most in the direction of the annual growth rings (tangentially), about half as much across the rings (radially) and only in minuscule amounts along the grain longitudinally). This means that plainsawn flooring will tend to shrink and swell more in width than quartersawn flooring, and that most flooring will not shrink or swell measurably in length. Generally, flooring is expected to shrink in dry environments and expand in wetter environments. Between the fiber saturation point and the oven dry state, wood will only change by about .1 percent of its dimension along the grain (lengthwise in a flatsawn board). It will change by 2 to 8 percent across the grain and across the annular rings (top to bottom), if quartersawn; and 5 to 15 percent across the grain and parallel to the annular rings (side to side), if plainsawn. Wider boards tend to move more than narrower boards. Movement in a 5-inch-wide plank is more dramatic than in a 2 1/4-inch strip. The ideal moisture content for flooring installation can vary from an extreme of 4 to 18 percent, depending on the wood species, the geographic location of the end product and time of year. Most oak flooring, for example, is milled at 6 to 9 percent. Before installation, solid wood flooring should be acclimated to the area in which it is to be used, and then tested with a moisture meter to ensure the proper moisture content.
A wood’s weight and moisture content: Wood is hygroscopic–meaning, when exposed to air, wood will lose or gain moisture until it is in equilibrium with the humidity and temperature of the air. Moisture content (MC) from 5 to 25 percent may be determined using various moisture meters developed for this purpose. The most accurate method in all cases, and for any moisture content, is to follow the laboratory procedure of weighing the piece with moisture, removing the moisture by fully drying it in an oven (105 degrees C) and reweighing. The equation for determining moisture content is MC% = weight of wood with water – oven-dry weight / divided by oven-dry weight X 100.
EXAMPLE of EXPANSION/SHRINKAGE – Oak expands and contracts across the grain with moisture change. The difference in how the flooring behaves is significant since plain sawn expands and contracts across the width of the board, while quartered in theory get thicker and thinner. Quartered has considerably more dimensional stability and does not respond to season change as does plain. Using this property, many old Eastern homes in this country had their oak floor installed after the base was applied to the wall and the oak floor was fit tight to the base-years ago-with no problems-quarter sawn flooring only.
Everyone involved with hardwood floors must take all precautions possible to avoid storing, delivery, installing, or maintaining floors in the presence of moisture or dampness. Guaranteed, if the wood is exposed to moisture it will react. It must acclimate where it is to be installed and guidelines for wood acclimation, installation and moisture related issues are available from NOFMA and NWFA.
Solid wood flooring should be delivered to the jobsite and allowed to acclimate to the conditions in which it will be installed or near occupancy levels. Temperature and humidity should be monitored. Delivery should be after major projects have been completed and thoroughly dry, such as dry wall and masonry work. Doors and windows must be in. Testing of wood, or any subfloors should be performed and moisture levels should not exceed 12-14%. Drainage- It’s vital the grading should be directed away from the facility to prevent unnecessary moisture problems. Basements and crawl spaces need proper ventilation. Polyethylene film of 6 mil in thickness must be used as a proper vapor retarder in any crawl spaces or where the soil line lies underneath. Vent crawl spaces and put own polyethylene as a ground cover where necessary . This vapor barrier will protect the sub floor from the normal moisture produced by the soil. This must be done wherever wood flooring is installed and used.
Keep the wood dry shipping, handling and storage Make sure the site conditions are dry. Acclimate the material on site in conditioned space for 4-5 days broken up into small lots Solid pre-finished wood floors should acclimate, in open cartons, on site for a minimum 72 hours or until the floor acclimates to the environment. To prevent the later pain and suffering of flooring failure, the two things you should do are 1) get a calcium chloride test kit to determine the amount of moisture moving through the concrete slab and 2) get an alkaline test kit. Either of these products can be purchased at a flooring supply or home store. You should also have a meter which measures the temperature and humidity of the airspace. All test results must be recorded for any unfortunate future problems, which hopefully you’ll avoid by paying attention to what has to be done on the front end first. Rush or eliminate any necessary steps and you’re bound to have a problem arise. This is not a surprise you want to have.
If you have high levels of either moisture or pH, there are some actions you can take. There are some concrete sealers that can be used which may lessen the moisture AND pH to acceptable levels… but there are no guarantees! Be careful… choosing the wrong sealer can make a bad situation worse! So be sure to purchase a sealer that is compatible with the flooring adhesive.
The popularity of wood and its beauty cannot be denied. In commercial space you have to remember what wood will naturally do. It will dent, scratch, gouge, the finish will dull or wear off, it will expand and contract, it can be chipped and marred. Spiked high heels, a small stone in the sole of a shoe or in the wheel of a delivery cart, items or packages dragged across the floor, will all damage the wood and this is what wood does. All the things you can do to a tree in the forest you can do to the wood floor. Maintenance cannot be done with wet mopping; this will cause dimensional changes in the product that are self induced. Wood is also noisy and will require more care. Carpet, in contrast, will hide dust and soil. Wood will magnify these things because it sits on top of the floor. Wood is a beautiful flooring material that requires care in a commercial environment. Know what you’re using, how it will or should perform and how it should be cared for before specifying, selling or installing this product. And never take the chance of installing wood in an environment where there is a hint of compromise to the product or the installation because, inevitably, it will come back to haunt you.
As with all flooring products you have to understand the inherent characteristics of them, where and how they can be used, how they have to be installed correctly, the influence of use and traffic on the product in the installation environment and how the product must be cared for. Taking all of these factors into consideration and having answers for all the questions that will come up will allow you to have a successful installation and satisfy the end user completely.
Author – Lewis G. Migliore – The Commercial Flooring Report
LGM and Associates – The Floorcovering Experts