Finishing an underlayment patch


Mechanically preparing a substrate

In my more than twenty years in the substrate patching and leveling business, one of my primary objectives has been to educate installers on the proper preparation of substrates. Something emerged recently that has caused me to have serious concerns.  Some individuals representing manufacturers of patching and leveling compounds touting that their products can be installed with “no” prep required. They claim that they have “new” technology and that you can simply mix and pour or place the product onto any concrete slab and their products will perform as a suitable substrate to receive even the most demanding floor coverings. 

Seasoned flooring installation professionals understand that long-term performance of cementitious patching and leveling compounds and proper substrate preparation go hand-in-hand.  Working with Ardex, a manufacturer of substrate preparation products for more than 60 years, I can assure you that there isn’t any “new” technology that allows you to install products without doing at least some level of prep.



Hand grinding a concrete substrate

Everyone is looking for an edge. Make note of what is actually being said, and then call the technical department of the product you are using, look up their literature or on their website and verify the claims. You’ll find out that, in fact, you do have to do some prep with any product on the market today.

The first wave of the no prep claims came my way from my colleagues in sales and marketing who were hearing it from our field sales professionals.  I told them to stop and think about what they were hearing and then think logically about the term “no prep.” I went on to explain that by simply redefining our substrate preparation recommendations, we could make contractors understand that there is always some level of substrate preparation required on every job. It’s only the amount and method of prep required that varies.   



A self-leveling underlayment is applied over a concrete substrate.

Every project that requires leveling or patching has its own set of unique jobsite conditions.  Questions to ask:

• What type of substrate?

• Is any contamination present?

• Are there curing and sealing compounds on the surface?

• Any existing floor coverings or adhesives present?

All of these and other conditions can vary from job to job.  Each set of unique conditions has a very specific series of steps required to prepare the substrate prior to installing the patching or leveling compound and then, the finish flooring. 

We decided to redefine the requirements for substrate preparation that we have been providing here in the U.S. for 30 years, re-categorize them into a set of steps that are clearly selected for a given set of jobsite conditions, and provide our customers with the best recommendations for installation success. 



Applying a self-leveling underlayment over a wood subfloor.

In other words, what amount of prep is proper for this specific job?  Thus the Proper Prep initiative was born. The great thing about Proper Prep is that the guidelines are available to any flooring installation professional for all projects, regardless of the products they select. 

Whether its self-leveling or trowel applied, deep pour or skim coat, requires fast drying or not, everyone can take advantage of the Proper Prep guidelines for virtually every jobsite. For example, the proper amount of prep for a job could be to broom sweep (no sweeping compounds, thank you) and vacuum the substrate, prime the surface with the appropriate primer, allow it to dry, and then install the leveling compound in accordance with manufacturer’s recommendations.  In this case, we can all agree that substrate preparation is minimal and likely, will not add a substantial amount of cost and time to the installation. As minimal as the prep is for this project, it is still not a “No Prep” situation; rather it is a Proper Prep recommendation. No prep….No!  Proper Prep…..Yes!



A self-leveling, self-drying concrete topping applied over ceramic tile.

There are a number of conditions that occur on jobsites ranging from the example above requiring the most routine preparation practices to more complex recommendations that require you to plane off a full half-inch of concrete that has been contaminated with oil or grease. There are waxed based curing compounds that have to be removed, but there are some curing compounds and sealers that are already chemically compatible with cementitious materials, such that they don’t have to be shot blasted off of the floor. 

On some renovation projects, we may run into some old, weak patching compounds that will jump off of the floor on their own and therefore we help them along by employing some method of mechanical prep. There are other patching and leveling compounds that we find on projects that have been down for 20 years that you have difficulty removing even with a jackhammer. If that is the case, then leave them their and install a demonstration area over them (after sweeping, vacuuming and priming, of course) to ensure that the system will perform as expected.  In each case, we employ the proper amount of preparation necessary for the precise jobsite conditions for each individual job.

Proper Prep is going to vary from job to job, floor to floor and sometimes even room to room.  The bottom line is, if you follow Proper Prep recommendations on every project, you will optimize the cost of installation and make the most economic choice for your customer that will result in the successful long-term performance of the entire flooring system.

In keeping with recommendations made by the flooring manufacturers, the surface of the substrate to which their floor coverings are to be installed must be clean, sound and solid, meaning no contaminants or weak materials on their surface.  While not all flooring manufacturers have identical recommendations for what constitutes proper prep, the resilient floor covering manufacturers have come to a consensus as to what constitutes proper substrate conditions to receive their vinyl, linoleum, rubber, and other polymeric flooring. There is a document in place that we can all follow as a guideline. ASTM F710:  Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring. This was developed by manufacturers, end users, and interested parties who agreed on certain specific conditions that need to be met prior to installing their flooring.  While this document was not developed for carpet, ceramic, wood, or other flooring materials, it helps to establish a basic set of requirements for all flooring structures.

Out of sight, out of mind…until the flooring becomes loose or detached from the substrate! The weakness in the substrate may require only a few weeks to begin showing signs of failure, but it could take months or more continuous traffic before the failure occurs.  A failure that occurs in the first few years is not acceptable to a flooring manufacturer that offers a 10-year warranty.  They want to be certain that their material will perform to its optimal potential.

By following a few simple proper prep rules, we can meet the requirements of the flooring manufacturers by providing a set of substrate conditions that will allow their products to perform successfully long-term.  Concrete must be structurally sound and solid.  While there is yet to be an industry consensus as to what constitutes a “sound” surface, a straw poll of a number of my colleagues in various disciplines both here in the United States and in Europe, can generally agree that the surface should have a tensile-pull strength in the neighborhood of 150 – 200 p.s.i. 

What about going over existing patching or leveling compounds?  A good rule of thumb is to follow the same guideline above for the strength of the surface of the concrete. The bond of the existing patch to the concrete should be at least as strong as the concrete itself. Another simple rule is to remove known contaminants. A large amount of concrete in the United States is cured by using wax-based curing compounds.  Patching and leveling compounds, along with flooring adhesives won’t bond to wax any more than they will to grease or oil.  These types of materials must be removed from the concrete completely.

Along the same lines as wax-based compounds, there are often chemicals applied to cure concrete slabs that are called “dissipating curing compounds.” Ultra Violet (UV) light and traffic over the surface of the slab will cause these materials to break down and disappear. However, since each one of these materials dissipates at different rates under a variety of jobsite conditions that can occur, you can never be absolutely sure that 100% of the chemical has dissipated, therefore light mechanical prep should be employed to remove the residues that remain.

What about existing flooring adhesives? There is a belief in our industry that since many adhesives we use today are water based and that they are water-soluble, they have to be completely removed when the flooring is to be replaced. The truth is that there are very few (if any) adhesives that will dissolve in the presence of water; only once they have dried and therefore, don’t need to be completely removed (alkaline moisture is another issue).  By scraping an area of waterborne, non-asbestos adhesive down to a thin residue and testing it for solubility using warm water, one can determine whether it can remain or must be completely removed.

Another myth in our industry is that all concrete must be shot-blasted prior to installing patching or leveling compounds. Concrete that has been mechanically hard-steel troweled (burnished) and concrete that was moist-cured without the use of curing compounds does not necessarily have to be mechanically prepped other than to remove any surface contamination.  Unlike epoxies, cementitious patching and leveling compounds do not need a profiled surface to bond to.

Primers are a must for self-leveling. There maybe some contractors that will tell you that you don’t need to prime, just make sure the surface is dampened first.  Well, if you think that pushing some primer around with a broom is a prohibitive cost factor, try “dampening” the concrete substrate to an acceptable level.  What they don’t tell you is that the surface has to be “SSD – saturated surface dry”.  In other words, you have to completely saturate the slab with water while leaving no standing water on the surface.  And, you must maintain this condition throughout the pour. 

Primers are a necessity on self-leveling projects.  They temporarily seal off the concrete from absorbing too much moisture from the leveling compound making sure that you get optimum flow while minimizing pin holes – a flash patching nightmare that has to be corrected before installing most resilient floor coverings.

In summary, no prep DOES NOT, and SHOULD NOT exist in our world. By understanding exactly what conditions you have on your jobsite, you can select from tried and true proper prep methods to ensure the long-term successful performance of each of your flooring installations.