NWFA CI flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Hygroscopic definition

A material that absorbs and releases moisture from the surrounding air. Wood flooring is hygroscopic, so it expands in humid conditions and shrinks in dry conditions, causing seasonal movement.

Equilibrium moisture content (EMC)

The moisture content at which wood neither gains nor loses moisture to surrounding air at a given temperature and relative humidity. Interior EMC typically ranges from 6% to 11% across seasons.

Cupping vs crowning

Cupping: edges higher than center, typically from moisture gain on the top face. Crowning: center higher than edges, often from moisture gain on the bottom or from sanding a cupped floor flat.

Normal seasonal movement

Expected expansion and contraction of wood flooring as indoor humidity changes. Winter gapping that closes in summer is normal, not a manufacturing defect or installation error.

Acceptable moisture content differential

Flooring MC should be within 2-4 percentage points of the job-site EMC at installation. Larger differences increase risk of gapping (too dry) or buckling (too wet).

Subfloor flatness tolerance

Wood flooring typically requires subfloor flatness within 3/16 inch in 10 feet, or 1/8 inch in 6 feet. Verify with a 10-foot straightedge and record high and low spots.

Calcium chloride test

ASTM F1869 moisture test for concrete. Measures moisture vapor emission rate in pounds per 1,000 square feet per 24 hours. Compare results to the flooring manufacturer's stated limit.

In-situ RH probe test

ASTM F2170 test that measures relative humidity inside a concrete slab using embedded probes. Results are expressed as percent RH and compared to manufacturer limits, often 75-80%.

Acclimation purpose

Acclimation brings flooring MC into balance with the job-site EMC before installation, reducing post-installation movement, gapping, cupping, and buckling complaints.

Buckling cause

Buckling (floor lifting from the subfloor) usually results from moisture gain, inadequate expansion space at perimeter walls, or a tight installation with no room for movement.

Perimeter expansion space

A gap left between flooring and walls or fixed objects to allow seasonal expansion. Missing or inadequate expansion space is a common cause of buckling and squeaks.

Crush marks at edges

Compression damage on board edges caused by excessive swelling against tight joints or obstructions. Indicates moisture gain plus inadequate expansion allowance, not a manufacturing defect.

Mill defect vs installation defect

Mill defects (machining, finish, grading) exist before installation. Installation defects (flatness, fasteners, expansion, moisture) appear after. Inspection timing and pattern help separate them.

NOFMA grading rules

Industry grading rules that classify unfinished hardwood strip and plank by appearance characteristics such as knots, mineral streaks, and color variation. Grade is an appearance standard, not a structural one.

Natural color variation

Inherent differences in heartwood and sapwood color within a species. Variation is expected in natural-grade products and is not a valid defect complaint by itself.

Finish checking vs cracking

Checking is fine surface cracks in the wood or finish from rapid drying. Cracking usually follows board joints. Both are moisture-related and should be documented with MC readings.

Gapping diagnosis steps

1) Measure flooring and subfloor MC. 2) Record indoor RH and temperature. 3) Check installation date and season. 4) Compare to EMC. 5) Determine whether gaps are seasonal or permanent.

Squeak cause analysis

Squeaks come from movement between boards, subfloor, or fasteners. Common causes are inadequate fastening, subfloor deflection, or seasonal shrinkage opening joints. Not a finish defect.

Photographic documentation

Inspectors must photograph conditions with scale references, date stamps, and orientation notes. Photos support findings and must be taken before any repair or sanding alters the evidence.

Moisture meter calibration

Verify meter accuracy with a known reference before each inspection. Record meter make, model, and calibration status in the report so findings can be independently verified.

Species identification

Identify species by grain, pore structure, and color. Species affects expected movement, hardness, and grading. Misidentification undermines moisture and defect conclusions.

Inspector report components

A report should include scope, date, parties, site conditions, measurements, photo log, findings, probable cause, applicable standard, and recommended corrective action, without assigning legal liability.

Relative humidity recording

Record indoor RH and temperature at the time of inspection. These values determine EMC and are essential for judging whether moisture-related conditions are expected or abnormal.

Subfloor deflection

Movement of the subfloor under load, often from undersized joists or spans. Deflection causes squeaks, joint movement, and finish cracking, and is not a flooring manufacturing defect.

Fastener schedule compliance

Verify nail or staple spacing, angle, and placement against the manufacturer's instructions. Improper fastening causes squeaks, edge lifting, and face-nailing complaints.

Delamination vs finish wear

Delamination is separation of finish layers from the wood, often from moisture or adhesion failure. Finish wear is abrasion from traffic. Each has a different cause and remedy.

Acclimation documentation

Records showing flooring was stored on site at proper temperature and humidity, with MC readings taken before installation. Missing records weaken any defense against moisture complaints.

Inspection timing rule

Inspect before any repair, sanding, or replacement. Altering the floor destroys evidence and can make cause determination impossible. Document conditions exactly as found.

Concrete vapor emission limit

Manufacturer limits for concrete moisture typically range from 3 to 5 pounds per 1,000 square feet per 24 hours (calcium chloride) or 75-80% RH (in-situ probe). Follow the specific product's instructions.

Crawl space ventilation

Adequate crawl space ventilation and a vapor barrier reduce moisture migration into the subfloor and flooring, preventing cupping and buckling. Poor ventilation is a common root cause.

Grading vs quality

Grade describes appearance characteristics allowed in a product. It does not measure installation quality or structural performance. Complaints about grade must be judged against the stated grade rules.

Corrective action recommendation

The inspector recommends a remedy such as humidity control, re-fastening, sanding, or replacement, based on the identified cause. Recommendations must be specific and tied to the finding.