If you own a new model car, there is a chance that your car offers a “self-parking” or park-assist feature, making it easier to parallel park or get in and out of tight spaces. This technology is not new. The first patent for self-parking was filed in 1938 by Brooks Walter but World War II started in 1939, shelving the technology, according to slashgear.com. Walter would give it another go in 1953, but it just never quite took off. The feature made use of the fifth wheel that was positioned on the back of cars at that time. The tire would drop down to the road and pivot the car a full 360-degrees if desired. While this feature seems remarkable and certainly ahead of its time, it is a bit misleading. The term “self-parking” is more akin to park assist as a driver is still needed to operate the car as well as activate and control the feature. 

Self-leveling underlayments (SLUs) in the floor prep world have undergone a similar terminology transition, removing any doubt of their capability. 

SLUs as they are commonly known, like self-parking, are not new. Ardex introduced them to the United States in 1978 in the form of its K-15 product, according to Pat Cunningham, manager of technical services, Ardex. From there, other manufacturers have designed their own SLU products. The term “self-leveling underlayment” is a bit of a misnomer as SLUs do not apply themselves and do not achieve “level” on their own. 

To remedy this terminology misrepresentation, the American National Standards Institute (ANSI) committee made up of 69 members voted to update the ANSI A108 document to include A108.T (T for terms) to provide a more comprehensive explanation that reflects the product’s actual attributes. 

“It is flowable,” said Scott Carothers, academic director, CTEF. “It is a hydraulic cement. So, the statement now is ‘Flowable Hydraulic Cement Underlayment/Self-Leveling Underlayment.’” 

The A108.T standard defining Flowable Hydraulic Cement Underlayment or FHCU was effective as of January 2024. Prior to this change, the ANSI committee worked for two years to rewrite the A108 document, specifically A108.01 General Requirements: Structures, Substrates, and Preparation of Tile and A108.02 General Requirements: Workmanship for Tile Installation. Following that update came the creation of A108.T to define the terms within the A108 document. 

“Prior to that time, some terms were a part of the various ANSI documents, but many of them had never been defined,” Carothers explained. 

He notes that the A108.T standard replaced the original A118.16 standard for SLUs.  

“The FHCU nomenclature really came from the tile side and the ANSI specs associated with it in order to get substrates flat and smooth, primarily concrete,” said Cunningham. “It better describes what [SLUs] are. These are going down at an 1/8” to a ¼" to 3/8”, maybe a ½”. They’re not conformed to the undulations of the substrate; you have to manipulate them, so it’s not necessarily self-leveling per se.”  

Logan Reavis, director of technical services, MAPEI, pointed out that over the years tile size has increased therefore “the requirement for flatness became more and more important in the tile industry.”  

The issue centered on the term “level,” according to both Reavis and Carothers.  

“The name change was really a request from labor,” said Reavis. “The term ‘level’ became problematic especially on large projects where that was interpreted because the name of the product was also a requirement of the scope of what they were doing when using these products. So, because the ANSI standard in the tile industry talks about flatness, it doesn’t talk about level, right? That was the issue.” 

Reavis points out that there are instances where a project needs to achieve flat but does not need to be level like in the case of creating float to a drain in a shower or outdoor space.  

The ultimate goal in addition to achieving “flat” is ensuring all of the different components that make up the FHCU are equally distributed across the application, according to Reavis. “Everywhere [the FHCU] reaches, that same mix of aggregate, cement and polymer has to be equal throughout so it builds appropriate strength, and it can perform. There is a lot of engineering that goes into that.” 

The skill required to apply FHCU/s/SLUs goes beyond simply dumping the mixed product on the floor and watching it fill in the low spots. According to Cunningham, Carothers and Reavis, specialized tools and procedures are necessary to fill low spots and navigate high spots as well as break the surface tension. This also includes utilizing a primer formulated to work with the FHCU. 

The flow rate is highly dependent upon the primer, according to Carothers. “You must use the manufacturer’s primer,” he said. “Primer does two things. It is a bonding agent, yes, but it also increases the flow rate of the product because it takes away any hot spots or any kind of moisture absorbing issues in the substrate.” 

Ardex, MAPEI and CTEF offer training on FHCUs where attendees will learn about the various ANSI standards that govern the different aspects of FHCUs. They will learn about the different products used including primers, application techniques, required specialized tools and the difference between substrate flattening versus substrate leveling. Additionally, all three make a point to explain the switch from SLU to FHCU, an important distinction going forward.  

“I do think it is an interesting example of collaboration within the industry,” said Reavis. “And really everyone coming together to try to understand each different entity and segment within their industry.”