NASCLA Accredited Commercial General ContractorFinishesHard
A contractor is installing a moisture-sensitive engineered wood floor over a concrete slab. To prevent cupping, buckling, and delamination, which of the following is the most critical step to perform before installation?
- AApply a sound-dampening underlayment.
- BConduct a calcium chloride test or relative humidity test on the slab.
- CInstall a vapor retarder directly beneath the concrete slab.
- DAcclimatize the flooring materials for 24 hours.
Show answer & explanationAnswer & explanation
Correct answer: B. Conduct a calcium chloride test or relative humidity test on the slab.
For moisture-sensitive flooring over concrete, it is critical to determine the moisture content of the slab. A calcium chloride test or an in-situ relative humidity (RH) test provides quantitative data on the slab's moisture emissions or internal RH, which dictates the need for and type of moisture mitigation system required.
Why the other options are wrong
- A. A sound-dampening underlayment addresses acoustic properties, not moisture migration from the slab.
- C. A vapor retarder beneath the slab is a good practice during concrete pouring, but it does not guarantee the slab's surface is dry enough for flooring, especially if installed incorrectly or damaged.
- D. Acclimatization is important for flooring, but it does not address potential moisture issues originating from the concrete slab itself.
Concrete Moisture Testing
Methods used to quantify the moisture content or moisture vapor emission rate of a concrete slab, crucial for preventing moisture-related failures in flooring installations.
- Calcium Chloride Test (ASTM F1869): Measures moisture vapor emission rate (MVER).
- In-Situ Relative Humidity (RH) Test (ASTM F2170): Measures internal RH of the slab.
- Results dictate the need for and type of moisture mitigation systems (e.g., vapor barriers, epoxy moisture barriers).
Memory trick: Slab's hidden dampness, test it first, save the floor's goodness.