Bamboo and Exotic Wood Floors - Strange Greenwood bamboo discoloration

About 6 weeks after a 2nd floor naildown install of solid 5/8" bamboo over plywood, there began to appear a deep yellow stain that went partially accross the boards. It almost looks as though someone has swiped a paintbrush filled with yellow paint across the board. Within a couple of months, about 15 boards scattered randomly through 3 rooms changed. There is no obvious pattern to the locations of the boards: some see foot traffic, some have never been walked on, some are under area rugs, none really get direct sun. The floor is only dry-mopped, no water or cleaners have been used. Looking at the cut end of one of the discolored boards, it appears that the stain goes into the top layer of wood about 1/8". The importer, Greenwood, sent out an inspector who checked ambient conditions, board moisture and several other things and concluded that it was an installation related problem. He claimed that the staining was caused by asphalt contamination due to the 15# roofing felt used as an underlayment and/or residue from the resealed street outside the house. Since Greenwood requires the use of roofing felt with its installs and the street was resealed months after the problem occured, the installer brought in another inspector. The second inspector stated that the problem was clearly in the boards and had nothing to do with asphalt contamination. Unfortunately, he also believes that since Greenwood's warranty has an "as-is" clause, there is no basis for having the discolored boards replaced. Greenwood is sticking to the asphalt story in spite of the facts. Has anyone ever seen this type of strange discoloration? Does anyone have experience with Greenwood's "as-is" warranty?

Thanks

If no alkaline cleaners, which can cause yellowing, were used, the variation in color is likely due to natural variations and shadings in boards. Typically, manufacturers separate bamboo boards by shade at the factory. There are no standards for shading, so shade differences may vary greatly.

Even with separation by shade differences, there will likely be some shade differences. Thus, when installing, it is best to pull boards from several boxes as it is installed in order to achieve a random effect as you describe. Shade differences tend to become more evident as the wood is exposed to light and oxidizes.

Keep in mind that natural shade differences are not considered a manufacturer's defect. Mother Nature's products naturally have shade differences. Even in solid hardwood flooring, you will find different shading and graining. No two boards are alike.

Thanks for the thorough reply. No cleaners of any type have been used. And while I'm familiar with, and expect the typical and sometimes significant color variation in wood and bamboo floors, there is nothing natural about this. Think the color of a deep mustard. The kind of vibrant color that causes visitors to notice immediately and ask "What happened here?" The yellow stains have a very distinct edge that crosses the individual strips within a plank but does not cover the entire board. It looks so much like a painted brushstroke that I wonder if it isn't something like some of the adhesive leeching up from where the layers are joined. I realize that it difficult to picture this without actually seeing the floor, but neither of the certified floor inspectors consider this a natural variation in color.

"
While our Bamboo flooring manufacturers attempt to identify the contents of each carton as "light" or "dark", there remains a range of colors within each category. The color determination is subjective and natural products are unpredictable in color consistency. To avoid color "blotches", the installer should work out of 3 separate cartons, alternating planks from each carton to produce a floor with a pleasing collage of colors."

http://www.greenfloors.com/HP_Bamboo_Installation.htm

The installer followed the procedure that you descibed and worked out of between 3 and 5 boxes. As a result, we do have a variety of the normal color variations throughout the house. But remember, no one that has looked at this, not the installer, the GC, either floor inspector or the importer, for that matter, thinks that this vivid coloring is normal. The only questions on the table are: What caused it? and What is to be done? To add to the mystery, the discoloration of these boards did not begin to appear until a few weeks after the install and continued to develop over time, although we haven't noticed any new problems lately.

appear a deep yellow stain that went partially accross the boards

IF the stain goes across more than one board side by side, then it is without doubt site related. That being the case, it would appear to be asphalt tracking. It requires only the smallest amount to cause a deep yellow stain.

If the stain is contained in single planks randomly dispersed through the floor, then there is an issue with the material itself. Regardless of warranty issues, the solution is to replace the individual offending planks.

Good luck