Inspector’s Report: When in Doubt, Reach Out

pre-finished bamboo flooring adhesion failure
Pre-finished bamboo flooring adhesion failure.

I was called out on an inspection in which pre-finished bamboo flooring had been installed over a concrete substrate below grade and had failed. There were a few things to investigate to get to the bottom of the cause. Was it the adhesive, the substrate, the installation method, or a combination of everything leading to the problem? Let’s look deeper.

The flooring materials were purchased at a big box retailer, and the installer used the recommended private label adhesive, trowel, and installation methods. On site, the installer noted that the existing substrate was concrete. Still, he did not want to do any kind of “prep” or “skim coating,” as he did not want to be blamed for any adhesive failure of a “reaction between adhesive and coating materials” that might occur with this type of installation. The installer took moisture readings upon delivery and noted between 7.9 percent – 18.3 percent readings. During installation, the installer used the recommended trowel provided by the manufacturer and followed installation instructions.

The contractor involved in the project noted that the concrete floor substrate was inspected prior to installation, and no issues had been noted. He also noted that there was styrofoam insulation and specialized drainage mats installed at the back wall of the home due to the significant amount of below-grade sections of the foundation walls being subject to water intrusion.

Pre-finished bamboo flooring cupping.
Pre-finished bamboo flooring cupping. Photos courtesy of Kelly Ragalie.


Lack of adhesive on concrete subfloor.
Lack of adhesive on concrete subfloor.

Upon my inspection on-site during destructive testing, I was able to lift the pre-finished bamboo flooring off the substrate with minimal effort. The adhesive had not adhered to the concrete, and there was visible moisture in some sections. It also was observed that the concrete flooring was “shiny and dark” in appearance.

After investigating the adhesive and installation requirements of the material’s manufacturer, it was noted that “concrete substrates must be free of sealers, curing compounds, stains, or other coatings, and should have no reflection of light.” In addition, a porosity test should be performed to ensure the concrete is porous and should be to a “broom finish.” When bamboo flooring is being installed, the concrete must include a calcium chloride or RH in-situ moisture test.

Sheen on concrete subfloor.
Sheen on concrete subfloor.

Sometimes trying to “avoid” a problem can cause other, bigger problems in the long-run. Installers should read manufacturer instructions and guidelines carefully for each product they will be using. Ensuring products are compatible with one another and performing each task specified by the manufacturer is required. When in doubt or when using a new product, try reaching out to the technical departments with questions or concerns and asking for assistance. Every manufacturer has a group of professionals that are able to walk you through each of their products. This is a great way to avoid falling into a potential trap by trying to escape blame or skipping steps. In the end, you will be confident in your reliable installation, and the steps you take to do so will be backed up by the proper use of the products.

Kelly Ragalie is an NWFA Certified Wood Flooring Inspector, Certified Sand and Finish Professional, and Certified Sales Advisor. Ragalie is the owner of Stafford Inspection Services, co-owner of Treadline Construction, and a technical sales representative for Loba-Wakol. She can be reached at

2 thoughts

  1. Kelly we installed 13 years of non stop containers of solid T&G bamboo flooring, all were installed on concrete and all installed using Elastilon and Poly plastic sheeting, and in all those years and hundreds of thousands of square feet we never had one Bamboo floor come back at us. Glue down over concrete is where all the problems lie and the Elastilon method with the poly plastic will stop all these failures of solid over concrete…. This is not meant as an advert but as a solution over concrete for solids. While the rest of the world had its issues with solid bamboo we never had one issue and even here in USA there are many successful Bamboo floor installations which have used this method of installation.. With a hydroscopic product that moves being glued over a hydroscopic slab that does not, can be a recipe for disaster, just one failure hurts as in this case and unfortunately with all the specifics as there are so many things that can create a problem there will always be one to pin it onto the installer as so much can go wrong Floating floors are becoming more and more acceptable and we do know they are a safer option due to the poly plastic and its zero perm rating.

  2. “Every manufacturer has a group of professionals that are able to walk you through each
    of their products.”

    Oh please. It’s wood (bamboo through a broker in this case no doubt) and everyone private labels one of about five adhesive manufacturers. Instructions are rampant with cutting and pasting other companies’ instructions “technical expertise”. Random disclaimers are added because last time they walked away from an inferior product exposure on an unrelated technicality and next time they might not have that out – even though it is materially the same product/same mill as ten other companies offering it under a different “brand”. You give way too much credence to most flooring technical “departments”.

    But it’s an excellent report explaining in detail the installer’s compounding mistakes. Thank you.

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