Case of the Month: Swelling Floor Planks

Sep 1, 2017 by

The homeowner’s bedroom floor was laid with laminate hardwood tongue-and-groove planks, over a slab-on-grade concrete pad. The flooring was swelling and lifting, presumably because of moisture. GEI was assigned to identify the predominant cause and determine the approximate age of the damage seen.

Swelling and “tenting” of flooring in bedroom

Our expert visited the property and the homeowner accompanied him on his inspection. The property was a single-family residence of timber framing with a stucco exterior finish and a plaster interior finish under a composition shingle roof. It was constructed circa 1972, according to the Los Angeles County Assessor’s web-site. The residence was not located in an active fault zone but was located in a liquefaction zone. As such, the building would be prone to damage from smaller (<3.5M) seismic movements.

The expert took a series of normal light photographs of the site and also included infrared photographs of the floor surfaces.

Gapping of floor finish

 

Edge of flooring sample showing tongue and groove

The rear portion of the residence was added as the later stage of site development. A building permit was approved by Los Angeles Department of Building and Safety in 2014 for a ground floor addition of about 200 square feet for a new family room.

The inspection of the exterior showed that the landscape required lowering to comply with the building code requirement of a 4-inch clearance between foundation weep screeds and the soil (or, in this case, mulch layer). Otherwise, the exterior was unremarkable and did not indicate any potential water entry sites. The rear yard had sod and appeared to be well drained. A local plumber tested the interior plumbing drain lines and the pressurized water lines. He found no drain line leaks nor pressurized water line leaks.

Concrete sub-floors are not required by the Building Code to include a vapor barrier underneath them. They are therefore subject to intrusion by groundwater, in the form of water vapor. Such groundwater as exists under every building is continually moving upward into the concrete because the concrete is porous and contains micro-cracks. In addition, because the area soils are subject to liquefaction during seismic events, concrete sub-floors are prone to forming many additional hairline cracks. The micro-cracks formed from the original curing of the cement paste in the concrete, the cracks that formed because of seismic activity, and the porous nature of concrete all allow and encourage movement of groundwater upward from the underlying dirt by capillary attraction. If the flooring finish is laid without a vapor barrier, moisture will travel up into the finish. If the finish is wood or timber, this will result in lateral expansion of that finish. Such lateral expansion will form “tenting” or swelling of the finish. Water vapor movement is detectable using infrared cameras. The infrared photos that the expert took demonstrated this in the bedroom flooring.

The flooring planks that were installed in this particular home were manufactured by Tecsun Building Products, whose web-site included installation instructions. Those instructions clearly required the installation of a 4-mil vapor barrier and foam underlay.

Infrared camera view of the floor by “tented” area of floor, with moisture presence indicated by arrows pointing to change in color.

Our expert found that the floor finish panels had “tented” by swelling and rising off the sub-floor. Other areas of the bedroom floor sounded hollow when tapped, indicating their separation from the sub-floor with potential later “tenting” of the laminate finish.

Based on the foregoing, the expert’s opinion was that the predominant cause of the damage seen was the failure to properly protect the installed laminate flooring against moisture traveling up through micro-cracks and the porous concrete floor slab-on-grade foundation from the naturally rising groundwater. The approximate age of the cause of those damages was consistent with the age of the concrete floor slab.