Failure of Three Layers of Poor Subfloor Preparations

The Impetus

A general contractor, who is a personal friend, requested a flooring inspection in a 7,000-square foot house in Zephyrhills, FL. The sprawling home had been vacant and locked in foreclosure for a few years. During the period of vacancy, moisture damage had accumulated. The new home owner wanted the carpet and hardwood floors replaced throughout. This article is focused on the sub-floor preparation needed in the downstairs areas receiving the new engineered hardwood: the foyer, the office/library, the dining room, the hall, two steps, and the sunken living room. In our initial inspection, we instantly noted that portions of the hardwood were wet, loose, discolored, and/or rotten.

Residential Home Library in Zephyrhills, Florida – Hardwood Damaged by Moisture before Demolition

Residential Home Library in Zephyrhills, Florida - Hardwood Damaged by Moisture before Demolition

Our Task

Our task was to provide and install beautiful new wood floors. After the mildew remediation was completed by another contractor, we started with the removal of the old hardwood. We perform the demolition using a ride-on scraper, chipping hammers, and other power equipment. The existing wood had been installed with Bostik’s Best adhesive, which created a bond considerably stronger than was required by the wood manufacturer. The extreme strength of the adhesive made for a very difficult take up. We would soon discover that the larger problem of the job was the irregular substrate under the hardwood. The substrate was noticeably unlevel, and the living room slab was sunken/sloped on the outside wall by approximately 1-1/2” to 2”. Worse still, the old hardwood was not releasing properly. Instead, thick layers of cementitious floor patch that were thicker than the engineered wood were coming up with the boards.

These two large sections of old wood were turned upside down to reveal construction dust and paint residue that prevented a solid bond of the floor patch to the concrete foundation.

The Underside of Two Large Sections of Old Wood Reveal Construction Dust and Paint Residue Caused Floor Prep Failure

The Cause

Upon removal of several boards, we noticed that there was a chalky deposit in the adhesive and in the patching compound of the previous installer. The chalky deposits were especially heavy on the slab nearer to the perimeter walls and was determined to be paint over-spray and drops from the drywall spackling or mudding process. This debris proved that the previous installer did not properly scrape, screen, or clean the slab. The contaminants on the slab prevented a solid bond of the floor patching compound. The Bostic’s Best held better than the old floor patch.

The old floor patch shattered like an eggshell. Notice the little fissures.

Notice the little cracks in the old floor patch on the underside of the hardwood removed.

The Potential Problem with Shattered Patch

The old floor likely shattered as a result of the demo equipment, but floor patch can break apart under an existing flooring after an installation. When floor compound cracks under a new flooring product like carpet or laminate, walking can cause crunching sounds as the chunks of floor patch rub between the fissures. In the case of the Zephryhills property, some of the old floor patch that remained bonded to the old wood during the removal process was held only slightly. Big pieces of the floor patch fell from the boards when carried to the trash collection point.

Large pieces of floor patch broke free and revealed three distinct layers of old floor float.

Three layers are evident after large chunks of floor patch broke off of the engineered hardwood.

Two More Layers

This seemingly small detail is significant because it revealed that more than one layer of floor patch had a substandard bond. In fact, based upon how the old patching compound split and cleft, we could three distinct layers of old patch. As mentioned earlier, we needed to correct the near 2-inch slope of the living room slab in addition to replace the floor patch. The homeowner was understandably unhappy with the discovery that the substrate was falling apart, but we were prepared to resolve this unpleasant surprise.

Side and top view of a layer of old floor patch was 3/4 of an inch thick (3/4″) thick.

Measure of 3/4-inch Thick Layer of Old Floor Patch

The Solution

Before making any compound applications, we applied a primer to the freshly cleaned slab from wall to wall.  Then, we made several deep-fill applications of leveling compound as to obtain a levelness within 3/16” over any 10′ radius.  Then, we applied scimcoats of floor patching material to perfect the consistency.  Next, we screened the final application of the compounds for smoothness and levelness.  Finally, we checked for acceptable moisture content in the slab and recorded the same.  (See ASTM F2170 (in situ probe test for relative humidity) and ASTM F1869 (calcium chloride moisture test for moisture vapor emission rate).)  After acclamation, we installed the new wood. The customer was very happy. Happy, indeed.

No Comments Yet.

Leave a comment

You must be Logged in to post a comment.