Let's Win the Concrete Floor Moisture Battle - Together

Impervious flooring. Water-based adhesives. Fly ash and slag pozzolans. Vapor retarders. Extreme surface pH. Fast-track scheduling. All are coming together and creating flooring failures.

Heightened Emphasis
There seems to be an increased sensitivity to flooring and moisture problems. One of our clients is refusing to use sheet rubber flooring. Why? Not because of the flooring material. It's a moisture-related, adhesive failure because the flooring is impervious.

Does the client know the root cause of this failure? I don't know. The consequence - banning sheet rubber flooring - is reactionary, not a solution. Will an alternative sheet flooring product solve the problem? No. A different impervious flooring is likely to have the same issues.

What's the Current Situation?
Moisture in the floor slab seeking equilibrium is the issue. Impervious flooring traps moisture in the slab that may re-emulsify the flooring adhesives and cause blisters from the vapor pressure.

With today's speed of construction, new concrete floor slabs will likely have moisture content exceeding the flooring manufacturer's recommendations. For existing floor slabs, there is no guarantee the moisture content will be acceptable, just because the slab is old. There may be no way of knowing the underslab condition and if a vapor retarder is present and functional.

To meet the schedule, the general contractor will direct the subcontractor to begin installing the flooring. The sub can refuse citing unacceptable substrate conditions. When the GC insists the floor be installed, the sub will request a change order for the cost of mitigating the moisture plus a time extension to complete the work. The GC can counter with threatened back-charges for delaying the project. The architect may need to negotiate a solution. And the owner will ultimately pay the price.

Current guide specifications place the responsibility for substrate inspection, moisture and pH testing, and acceptance in each finish flooring specification. The specifications are written to the general contractor, but the GC assigns the work of the specification to the installer. There may be multiple installers required for the several, sometimes many, floor finishes on a particular project. Each installer is responsible for examining and testing the substrates affecting his work. The testing requirements and the acceptance criteria for each flooring manufacturer may be different. There is no coordinated approach to the entire project.

See Conspectus Tech Tips that discusses concrete slab surface prep and moisture tests.

So What Can be Done?
We can ignore the problem, assuming the general contractor has sufficient control of the project schedule and sequence to allow the floor slabs to sufficiently dry before installing the flooring. However, the owner sometimes dictates the schedule by setting the completion date. So, be prepared for a mitigation and time extension change order.

We can try to help resolve the situation recognizing moisture problems will likely exist because of some or all the conditions listed at the start of this blog. Accepting that premise we can:

  • Specify the required testing and surface preparation separately from the flooring spec sections.
  • Require that a single entity be responsible for all moisture testing and all surface preparation.
  • Require all flooring installers attend the same preconstruction conference to review and approve the testing and preparation procedures plus a uniform acceptance criteria that will accommodate all floor finishes throughout the project.

By specifying a uniform approach for the entire project, the requirements will be more easily enforced and monitored. To ensure the best results, require testing be started early. Track and analyze the data to help identify opportunities to adjust construction materials and processes to improve floor slab moisture content for the entire project.

After Testing
When testing finds excessive floor slab moisture, the slabs must be dried or must be remediated to prevent the moisture from causing adhesion problems. Drying takes time and money, and both are unpredictable. Mitigation takes money and limited time to install another material. Regardless the owner will pay with time (delayed opening) or money (unexpected costs), or both.

Be Proactive
The specifier can help remedy the situation by planning for the floor slab's potential excessive moisture content by including mitigation as part of the contract.

  • Select a method capable of working with all the expected floor finishes.
  • Ensure the flooring manufacturers certify compatibility with their adhesives to avoid affecting flooring warranties.

Require mitigation to be bid, but carried as a contingency allowance or as a unit price. Then, mitigation procedures would be used only when required. All costs for mitigation would be paid from the allowance or by unit price. When mitigation is required for only selected areas, the excess allowance money would be returned to the owner.

Adopting a proactive approach allows the entire team to plan and accommodate likely field conditions. The owner will know the ultimate price. The contractor will have a predetermined solution to a highly probable problem. The installers will have an acceptable substrate. The work can remain on schedule. And everyone will be happy.

Need Help Getting Started?
We developed two independent specification sections: one for moisture testing, and one for surface preparation. We will happily send these files to you for your use. Just email me to request your copy of our testing and prep specs.

Now It's Your Turn...
How do you deal with concrete floor slab moisture issues? Comments welcomed.

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