As the focus on environmental responsibility gains strength among consumers and the wood flooring industry, bamboo flooring continues to be in the spotlight. Love it or hate it, it's something most contractors will have to deal with sooner or later. Of course, bamboo is technically a grass. "Solid" bamboo is constructed of rectangles of bamboo glued together, either horizontally or vertically. Engineered bamboo is constructed like any engineered floor, with wood layers below a bamboo wear layer. The newest type of bamboo construction is strand-woven, a process in which bamboo strands are saturated with an adhesive and fused together under enormous pressure, resulting in a product much harder than traditional bamboo flooring. Bamboo can be a great floor, but there are some caveats to take into consideration. Following are some things I wish every customer would understand about bamboo. (These are general guidelines; always follow the manufacturers' directions for the specific product you are installing).
Many installers are in the habit of leaving expansion at the sides of boards but not at the ends. That's usually fine for a typical hardwood floor, but bamboo does expand and contract along its length. Horizontal solid bamboo will expand and contract more than vertical bamboo, and strand-woven bamboo will expand and contract just like solid wood flooring.
People should have realistic expectations of how a bamboo floor will perform. Sometimes the Janka numbers lead people to think a bamboo floor will be more durable than it actually is in real-life situations. Bamboo fibers are strong, but the lignins bonding them together are weak. In a Janka test, a smooth, round ball is pressed into the material. With bamboo, the fibers are springy and tend to resist the ball. However, if you hit bamboo with a sharp object—like a stiletto heel or a small rock in the sole of your shoe—it will cut into a bamboo floor more than it would in an oak floor. An exception to this is strand-woven bamboo, for which Janka tests accurately predict performance.
With engineered products, it's important to keep bamboo's biological structure—strong fibers and weak bonding material between them—in mind. When a bamboo wear layer is exposed to very low relative humidity (RH), the fibers want to shrink and pull away from each other, but the fibers are held in place by the cross-ply structure of the engineered product, so they can't move. The weak bonding lignins can then break, creating cracks in the wear layer. If there's a situation where the RH is likely to get very low, well-acclimated solid bamboo may be a safer option.
Make sure the manufacturer of your moisture meter has done the proper testing for bamboo so you know what the correct adjustment is on your moisture meter. If you're using a pin meter, as you poke into the floor, make sure the prongs don't cross a glue line of the little rectangles glued together to form the floor, because you'll get a faulty reading. When you're buying bamboo, look for kiln drying that meets typical American standards: within 6 to 8 percent moisture content (MC). Lots of product coming in from overseas is imported with a MC of up to 12 percent.
Because solid bamboo flooring is made up of lots of little pieces of bamboo glued together, people often assume it doesn't need to be acclimated to the job site. Not true—even though there are many small pieces, they are all oriented in the same direction and will expand and contract. Solid bamboo flooring tends to acclimate quickly (three to seven days is typical), but is does need to acclimate. Strand-woven bamboo also requires acclimation, and it acclimates very slowly. In extreme climates, it can take up to 30 days for a strand-woven bamboo floor to acclimate to a job site. As with most engineered products of any species, engineered bamboo may not require acclimation (check with the manufacturer).
With the LEED (Leadership in Energy and Environmental Design) certification system, products may garner points under different categories. Under the "Rapidly Renewable Materials" credit, any solid and strand-woven bamboo flooring earns points, but engineered bamboo does not, since it contains wood. Under the "Certified Wood" credit, bamboo flooring may earn points if it is FSC (Forest Stewardship Council)-certified, but the value of FSC-certified bamboo cannot be applied to both the "Certified Wood" and "Rapidly Renewable" credits—you have to choose one.
Another credit rewards products with no added urea-formaldehyde. Traditionally, the adhesives used to glue bamboo flooring together have been urea-formaldehyde adhesives, which tend to off-gas long after being installed in a customer's home. Some bamboo products are now constructed with different adhesives, so they qualify for this credit. Strand-woven products are not constructed with urea-formaldehyde and all qualify.