About six months after installation, bubbles started to appear on top of a strand bamboo floor. I was called by the homeowners after they were unhappy with the results from the retailer's inspection.
The home was about 30 years old and was located in Florida. The flooring was a 5/8-inch-thick, 3-inch-wide plank glued directly to a slab on grade. There was about 1,400 square feet of the flooring installed throughout most of the main living areas. The flooring had acclimated inside the home with the air conditioning running for a month before installation.
The homeowner installed the flooring himself, and he used the adhesive recommended for the product, which is a two-step urethane that is both an adhesive and a moisture inhibitor. When used correctly, its label says it provides protection for up to 85 percent RH in the slab. The homeowner didn't do any moisture testing, and he said he didn't need it since the slab was 30 years old.
When I arrived to inspect the floor, it had been down for about a year. About 25 percent of the boards throughout the floor had bubbles, and on those about 10 percent of each board was covered in the bubbles. If you stepped on the bubbles they would burst and a sticky liquid would come out.
The installation itself looked professional-the slab had been flattened to within recommended tolerances and all the transitions were done well. However, the homeowner had not followed the recommendations for the adhesive/moisture inhibitor. This product is supposed to be flat-troweled on first to provide the moisture protection and then immediately spread again with the notched trowel, but the homeowner only applied it with the notched trowel.
During the inspection I measured the flooring's moisture content with the bamboo setting on my moisture meter, and the results came back with a range from 12-19 percent. In this area 12 percent is typical, but 19 is really high, even for Florida. Interestingly, the high moisture was not in correlation with where the bubbles were; in fact, the areas without bubbles had a higher MC. Also interesting was the fact that there was no other evidence of high moisture-there was no cupping or buckling anywhere in the floor. The homeowner didn't want any destructive testing, so I couldn't measure the moisture in the actual slab.
I consulted with a leading bamboo flooring expert to get his opinion, and he said that while resins bubbling up out of a strand bamboo floor isn't uncommon, he has always seen it with cupping and buckling. Once all factors were considered, my conclusion was that the failure of the floor was consistent both with deficient manufacturing (uncured resins) as well as higher-than-normal moisture conditions.
How to Fix the Floor
It's possible to sand this type of floor, but because of the risk of more resin emerging from the floor, the entire floor must be replaced, preferably with a different product.
In the Future
Always do proper moisture testing, follow the manufacturer's directions and buy a quality product. I'm an installer, too, and you better believe that if I'm going to glue a bamboo floor on a slab here in Florida, I'm going to use a reputable bamboo floor and a high-quality moisture inhibitor to minimize my risk.