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In this article, we will look at an underlayment installation that ended up being replaced due to a combination of problems. Generally, the reason for installing an underlayment system over a sub-floor is the fact that the sub-floor is not suitable for a direct glue application of floor coverings. The proper installation of the underlayment over an "acceptable" sub-floor is critical to the success or failure of the installation, as we will see.

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A brief history

A brief history: This is an installation in a school, approximately 3,500 square feet of vinyl composition tile (VCT) was installed over a 1/4-inch plywood underlayment. There are three classrooms, two of the classrooms have a one-inch plywood sub-floor, and one classroom has 2-1/4-inch strip hardwood flooring installed over a one-inch plywood sub-floor (Photo 1). After the underlayment was installed, the architect conducted a site inspection and noticed a ridge in the middle of each classroom along the entire length, after inspecting the ridge in the underlayment; the architect requested that corrections be made to the classrooms, prior to the installation of VCT, as the ridge would be in traffic areas. There was a meeting arranged with the architect, general contractor, structural engineer, flooring manufacturer's representative, and flooring contractor, where it was determined that the floor would be lowered from underneath in two of the classrooms. The high point happened to be over columns in the basement; approximately one inch was cut off the top of the columns to minimize the high spot. Two of the three rooms were dropped and level to within 3/8-inch across the 22-foot wide width of the rooms; it was determined that lowering the sub-floor in the third room would be a problem with the strip flooring, so no corrective measures were taken in that classroom. After the lowering of the sub-floor, the VCT was installed. Approximately two weeks after the installation the flooring contractor received a phone call from the general contractor stating that the floor was displaying movement and bubbles in random areas of the entire installation. The flooring contractor sent his installers out to make corrections, the installers removed tiles in areas that were displaying movement, fastened the underlayment with screws and replaced with new tile. Over the next week the flooring continued to display more and more bubbles six inches in diameter to one foot in diameter with movement up to 1/4-inch, to the point where another site meeting was held. The flooring contractor insisted that, due to the sub-floor being lowered after the underlayment was installed, the installation contractor was not responsible. The general contractor, knowing that the floor would not be accepted, removed the VCT tile and requested an inspection to determine who was at fault.

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The underlying issues

Photo 2 shows a level in the middle of the room that was not lowered; there was a high spot in each classroom running the length of each room; each room is approximately 22 feet wide. Photo 3 is the room that was not dropped; the photo shows at two feet there is a 1/2-inch variance of the sub-floor and underlayment from level. Photo 4 is showing the variance in eleven feet with a laser placed at the middle of the room to the wall; the laser was set level one inch above the floor; therefore, there is a variance of one inch in eleven feet.

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Photo 5 shows an area where the underlayment was removed; this room had the 2-1/4-inch strip flooring installed over a one-inch sub-floor. The blue tape indicates the placement of fasteners; 1-1/2-inch ring shank fasteners were used. A wood flooring adhesive was also used to randomly spot glue the panels to the subfloor. A straight edge was placed over the strip flooring to inspect for flatness of the strip flooring (Photo 6). There was a variance up to 3/32-inch Where the adhesive was still adhered to the sub-floor, there was height variance up to 3/32-inch above the strip flooring.

Photo 6
Photo 7 is one of the two rooms that have plywood as a subfloor. The blue tape indicates the fastening pattern and the round areas that are visible are where the panel was spot glued. The fastening pattern was very inconsistent as indicated in Photo 8, where there is a one-foot spacing between fasteners. So where does the responsibility fall? The flooring contractor pointed out the fact that the sub-floor was dropped one inch and there were no relief cuts made to the top of the sub-floor or underlayment; therefore the bubbles were caused due to compression stress to the underlayment. That is a valid justification to a point; here are some of the installation issues. o The justification of the sub-floor being lowered after the underlayment was installed was deterred by the fact that one classroom was left untouched, and that room was also displaying movement of the underlayment; also, there are two restrooms with a resilient flooring that have been flash coved in between the lowered classrooms and the classroom that was untouched. These were installed prior to lowering of the two classrooms, with no visible effects from sub-floor movement. o The levelness of the sub-floor should have been addressed prior to the installation of the underlayment. o The classroom with the strip flooring should have been sanded flat prior to underlayment. o Panels should have been installed at a right angle to the sub-floor panels. o The amount of fasteners used was not to manufacturer guidelines. There were 69 ring shank fasteners used in a four-foot by six-foot area where underlayment was removed. The recommended nailing pattern for a four-foot by four-foot panel is every four inches in the field, and every two inches at the perimeter; that equates to 192 fasteners for a four-by-four panel. o The length of fasteners used where there was a plywood only sub-floor, was 1-1/2 inches, the sub-floor is one-inch, the underlayment is 1/4-inch, the two equaling 1-1/4-inch. The manufacturer states that the nail must be a minimum of one inch long and penetrate a minimum 3/8-inch into the sub-floor but not protrude through the bottom of the sub-floor. o Adhesive was used to spot bond, which created more height issues and undulation of the panels. o The entire underlayment installation was skim coated. The manufacturer recommends that joints be sanded, and only use a patching compound where there is a 1/16-inch or greater gap.

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Unfortunately, the installation issues outnumbered the justification of the sub-floor being lowered, had the underlayment been installed properly, then perhaps the flooring contractor would have a legitimate defense.

The entire installation of VCT and underlayment was removed and new underlayment and VCT re-installed. There was also a time factor as the school was opening for classes within two weeks from the time that the flooring was being removed, putting more pressure on the flooring contractor, who was the low bid, to finish this project and possibly delaying other installations. Unfortunately, due to the lack of education or ignorance, the flooring contractor ended up paying for double the amount of VCT, underlayment, and labor, along with having to pay for the take up and removal of the first installation of VCT and underlayment by the general contractor.

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Needless to say, the flooring contractor was out thousands of dollars and lost credibility with the general contractor for future work.

The lesson to all of this, follow the manufacturers' recommended installation guidelines and educate and train youself and your installers to avoid these types of pitfalls that could ultimately put you out of business.