Installation: Subfloor prep tips from the trade

Home Inside FCNews Installation: Subfloor prep tips from the trade

September 11/18, 2017: Volume 32, Issue 7

By Lindsay Baillie


The success of any flooring project begins with the proper substrate preparation. That’s according to expert installers and manufacturers who say any mistakes during the earlier stages of installation can cause trouble for all involved—consumer, retailer and contractor—years down the road.

FCNews rounded up several installation experts who provided helpful guidelines to consider when preparing a subfloor.

Clean the area prior to installation. With hardwood subfloors in particular, the area must be cleaned and flattened before underlayment can be installed. “This includes removing all dust, dirt and debris by scraping or sanding the entire area,” Tony Buckhardt, senior certifier, CFI, explained. “Concrete floors should also be flattened and cleaned. However, concrete usually requires mechanically removing old adhesives, dirt or debris.”

The use of a bead blaster, sandpaper or concrete grinder is required by most manufacturers over the use of chemical removers, which can soak down into the concrete and cause bond issues.

Don’t skip proper priming. Proper priming is typically required by manufacturers in order to maintain a product’s warranty. As Mark Olson, INSTALL instructor, explains: “If a primer is improperly applied or, even worse, not applied at all, this increases chances of flooring failure and will void the product’s warranty. In addition, the replacement of the flooring will be disruptive to occupants, time consuming and can cost up to 10 times the amount of the original installation.”

When choosing the proper primer, installers should find out whether or not the floor is porous. “There are different primers for porous and nonporous floors, and the primer is important for the proper bond for the self leveler,” CFI’s Buckhardt added.

Furthermore, according to David Stowell, technical director, Schönox, HPS North America, installers should always prime when using cement compounds over gypsum-based materials—and vice versa.

Follow company mixing requirements. Manufacturers often test products in different time increments to ensure proper performance. They also have specific directions for mixing. To ensure optimal product performance, installation experts recommend users stick to the script.

“If it is not mixed correctly, or by the manufacturer’s recommended time, it will increase the chance of installation failure,” Olson explained. “It might also tarnish a contractor’s reputation and cost future business.”

Adhere to moisture test standards. More subfloor solutions depend on moisture test results. To avoid a potential issue, according to Schönox’s Stowell, installers should perform moisture tests per ASTM F2170 and ASTM F1869 standards.

Use the right product for the job. According to Greg Hunsicker, category business manager – flooring & finishing segments, Ardex Americas, it is vital for an installer to select the best moisture remediation, leveling and patch system for the job. “In addition, the proper preparation of the substrate is important to be certain you obtain a clean, sound, solid base for your prep materials.”

Repair moving joints and cracks. When an installer uses a self-leveling product for subfloor prep, he should also address moving joints and cracks in the substrate. “If not addressed and repaired, moving joints and cracks can transfer up and cause cracks in the finish,” said Dean Cunningham, technical service manager, Laticrete. “To allow for natural building movement against restraining surfaces, Laticrete also recommends that installers evaluate and isolate the area around walls, columns, penetrations and other building elements where movement may be anticipated.”

Contact manufacturers with application questions. All installation experts agree an installer should speak with the manufacturer if there are any questions regarding mixing or using the product. In addition, the installer should allow the technical services team to walk him through the installation.

It’s important to note that requirements and methods vary depending on the type of floor covering specified. “For example, some floor coverings require a light grind or shot blast to a specific concrete surface profile, while others require a more aggressive mechanical surface prep in order to achieve a tenacious bond,” Laticrete’s Cunningham explained. “In addition, slab moisture conditions such as relative humidity, moisture vapor emission rates and pH must be taken into consideration and measured in order to properly prepare a concrete floor for further treatment and ensure a successful flooring installation.”

Dress for success. Beyond the technical aspects of subfloor preparation, experts suggest installers wear proper cleats for each job. “Every flooring installer who works with self-leveling product will need to work directly with the product—blending pours as well as distribution,” INSTALL’s Olson explained. “Wearing cleats also ensures the primer that was installed beforehand will not be disturbed.”

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