Self-levelers, patches and skimcoats may not be the most glamorous part of an installation project, but they definitely are life-savers when an installer arrives on the job only to find the subfloor is not in any state to receive flooring. These products are designed to make installers’ lives easier and their jobs more profitable. We spoke with industry manufacturers about what novices and pros alike should know when working with these materials.

Tips for novices

Brett Mauney, Merkrete technical sales specialist, shared definitions for each type of product. “Self-leveling underlayments (SLUs) are used for leveling an entire surface area, typically from 1/8 in. to 1/2 in. Because of the fluidity of the SLU, it is important to dam off all areas that you do not want the material to flow into. Additionally, remember to follow the manufacturer’s recommendation for using a primer prior to the SLU application.

“Patching compounds are typically used for fixing indentations or uneven areas in floors. Patches are also used for ramping from one area to another. Only mix up enough material that can be used in a short amount of time as patching materials tend to dry quickly.

“Skimcoats are just as the name states—they are used for skimming over a rough surface making it smooth and ready for flooring installations. Skimcoats are also used for smoothing embossed surfaces typically over preexisting floors.”

The key to a successful installation is proper preparation. This includes knowing the capabilities of each surface preparation material prior to installation.”

– Arthur Mintie

Eric Kurtz, Bostik’s market manager for hardwood, resilient and surface preparation systems, said it is essential to select the right product for the right application. “For example, many patches and self-levelers on the market have moisture limitations and should never be used in areas with high moisture vapor conditions.”

“Also, especially for self-levelers, always use a primer,” he added. “Nearly every ounce of water in the mix is necessary for proper curing of the self-leveling underlayment. Failure to prime the substrate will allow a lot of water to seep into the substrate, starving the self-leveler of the water it needs to achieve full compressive strength.”

Ardex’s Seth Pevarnik, director of technical services, and Greg Hunsicker, business manager for flooring and finishing, offered some considerations when choosing an SLU for the job:

How thick do you need to go? Do you want a standard flow or high flow product? Standard flow products are a little heavier, have more body and often allow you to go up to multiple inches in thickness. High-flow products have a lower viscosity, and can be installed as thin as 1/8 in.

What is your substrate? Some self-leveling materials are more versatile and can go over almost any substrate. Others may be limited to installation over concrete. Always refer to the manufacturer product guidelines for clarification.

What is your timeline for installation of flooring? Some products are self-drying, allowing for the installation of flooring in as little as a few hours. Others may require a few days to dry.”

They also shared several questions to ask when choosing patches and skimcoats:

Do you need to skimcoat the floor to make it smooth? Do you need a ramp or slope to create a transition? There are products specifically designed to ramp, slope and create transitions that can be screeded into place.

What depth are you planning to install the product?  It’s common for a patch to have sand in it, allowing for applications up to multiple inches thick. Skimcoat products are commonly unsanded, in order to achieve a true featheredge when installing.

What is the substrate and how fast do you need the product to dry? Just as with self-leveling materials, consider your substrate and dry times to identify the correct product.”

According to Arthur Mintie, Laticrete’s senior technical services director, SLUs, patches and skimcoats do not require extensive training to use correctly. As long as the manufacturer’s instructions are followed, installers shouldn’t encounter any problems. “The key to a successful installation is proper preparation. This includes knowing the capabilities of each surface preparation material prior to installation such as working times, curing times and minimum and maximum thicknesses.

“If the substrate is in poor condition, whether that means not dry enough or not properly cleaned before using leveling products, the finished flooring performance will be compromised. Once the self-leveling underlayment, patch or skimcoat is installed, it is critical to check that the surface is as level as possible before installing the floorcovering. This step can prevent hours of corrective work and costly repairs later on.”

Jeff Johnson, MAPEI’s business manager for floor covering installation systems and substrate preparation, offered these suggestions: “If you are a DIY person, we would recommend you use a self-leveler that is a low-prep solution such as our Novoplan Easy Plus or Ultraplan Easy. These levelers do not require profiling of the surface and can be placed over a clean, properly primed surface without having to bring in a shot blast or grinder to prep the subfloor. The other thing to note for the novice is that self-levelers, when properly mixed, are very fluid, and any holes or gaps in the subfloor such as plumbing lines or electrical chases will act like drains, allowing the fluid leveler to pour through to the room below.”

“Another important aspect is how much water to add and how to mix the self-levelers,” he cautioned. “The common mistake made by novices and experts alike is to overwater the product to make it more fluid. The reason why it may not be fluid enough is that it is not being properly mixed. Always use the recommended amount of water—never more—and mix with a high-speed mixer to a smooth, homogenous consistency.

“Lastly, self-levelers, although they are fluid, do need some help spreading around, and it is recommended to have some sort of gauge rake available to push the leveler around to come to a uniform, flat thickness.”

According to Patrick Mukushina, H.B. Fuller Construction Products product manager, installers and contractors should familiarize themselves with the substrate before working with these products.

“Knowing if the substrate is porous cement, gypsum or an epoxy coating will help you understand how much primer to use and at what dilution ratio. If self-leveling, you will want to carefully measure the square footage in advance. Running short of a self-leveler in the middle of the job will create added difficulty.

“Knowing the limitations of the products in advance is also a key step in the process. Some products can be poured 3 in. deep, while some only go to 1/2 in. It is important to choose the right product for the right situation in advance. Also knowing the working time of the material is important. Some material sets up faster than others and you will want to know this and prepare for this in advance.”

Eric Carr, Custom Building Products senior director of product and channel management, echoed these sentiments. “First-time users and DIYers need to first do a thorough inspection of the floor/substrate that they are working with. This inspection will help determine what products they will need for the project. In addition, they need to make sure they have the proper products and tools for the project.”

J. Alex Keene, Dependable division manager, stressed to “always read the manufacturer’s instructions before installing any product. Second, mix a small amount of product first, before using more. This is to familiarize yourself with the product prior to using it in a large amount. Once a skimcoat or self-leveler has dried it is difficult to take off the floor, so ensuring you put it down properly is important. Third, watch any instructional videos online, if available. Dependable offers installation guide videos on all of our skimcoats and patches.”

David Stowell, Schönox HPS North America technical director, added: “Review the technical data sheets to obtain proper knowledge of the requirements of the substrate for the products you are installing. Perform moisture tests per ASTM 2170 or ASTM 1869. Remove all contaminants, residues and bond breakers. Check porosity and use the correct primer (i.e. porous or non-porous). Follow the bag mix ratios not to overwater the SLU, feather edge or skimcoat.”

Brett Fleury, USG product marketing manager, performance flooring, commented: “I highly recommend reading the subfloor preparation instructions, not just the mixing instructions. A significant amount of time is dedicated by the manufacturers to inform the end-user on the steps required to perform a successful installation. Properly preparing the substrate to receive the SLU or floor patch is the most important step to ensure the products can achieve a tight bond with the substrate. Mixing the product properly and installing it over a floor with bond breakers will not provide the long-term result that is desired.”

Tips for pros

Johnson said, “Seasoned professionals need to be aware of the temperature of the water used to mix levelers. Self-levelers are designed to flow and cure based on the use of room temperature (73 degrees Fahrenheit; 23 degrees Celsius) water. Using cold water is going to slow down the flow and cure of a leveler. Hot water will cause rapid cure and segregation, which will lead to a performance problem.

“Professionals also have more options on how levelers are mixed. Everything from five-gallon pails to 15-gallon mixing drums to high-performance mixing pumps can be used for self-levelers. Each method has its own unique nuances, but for all the basic rules apply. Maintain the proper water addition and temperature, mix to a smooth and homogenous consistency, protect the poured leveler from direct sunlight or heavy air movement, and you will achieve a perfect leveler application.”

Mukushina noted that seasoned professionals need to know the strengths and weaknesses of the products being used and what conditions are suitable for each product. “The installer would use a different dilution of a primer on wood than they would on concrete. There are also special self-leveler formulations that can be used over a single-layer wood subfloor, for example.”

He added, “Water demand is a factor, even for the professional. It might seem intuitive that all 50 lb. bags would use the same amount of water, but that is not the case. Each manufacturer creates their own formulations and this results in differences in the amount of water being added. Knowing the product and the manufacturer’s instructions are important, even to the seasoned professional.”

According to Carr, veteran installers need to ensure the moisture level of the substrate is appropriate for installation. “The key issue to look out for on concrete substrates is to determine the moisture level in the substrate. If the moisture level is excessive (typically above 85% RH) for the type of flooring that is going to be installed, moisture mitigation is needed before self-leveling. If the substrate is plywood, you will typically need to install a metal or plastic lath before pouring self-leveling underlayments.”

Pevarnik and Hunsicker stated that “Not all self-leveling products are created equal. Some are engineered to perform over wooden subfloors without the addition of liquid additives or mesh products, like Ardex K 22 F High Flow Fiber Reinforced Self-Leveling Underlayment. Professionals must also understand that most self-leveling, patch and skimcoat products are not suitable for damp applications, such as exterior use or under a moisture control system. For any application where the products could be indefinitely damp, be sure to use products designed to withstand these conditions.”

Mintie said installers need to adequately prepare the subfloor. “Some floor coverings require a concrete substrate to be lightly grinded or shot blast to a specific Concrete Surface Profile, while others require a more aggressive mechanical surface preparation in order to achieve a tenacious bond. In addition, slab moisture conditions such as relative humidity (RH), moisture vapor emission rates (MVER) and the level of alkalinity (pH), must be taken into consideration and measured in order to properly prepare a concrete substrate for further treatment and ensure a successful flooring installation.

“For plywood substrates, installers are recommended to apply subfloor adhesive to the top of the floor joists to prevent the plywood from moving around before self-leveling products are involved. Depending on the specified flooring finish, the appropriate type and thickness of the required underlayment then follows. Installers should check with their leveling manufacturer for compatibility with the various substrate types.”

Regarding plywood substrates, Mauney commented that “going over plywood will change how the products are mixed and applied. For example, when going over plywood you should use a latex additive for flex and bond instead of water.  Some products may have polymers or latex already built into the product for ease of use.
“Additionally, when going over either surface be aware of contaminants such as concrete inhibitors, paint, sealers, etc. These types of impurities may cause a bond failure. Follow manufacturer’s guidelines for properly preparing the surface before use.”

Kurtz added, “Once again, selection of the right product for the application is critical. When going from a concrete substrate to plywood, flexural strength becomes a primary concern, whereas moisture limitations become less important. In addition, we see too many flooring installers go over existing substrates without proper surface prep.  While surface preparation adds a step, it invariably makes the flooring installation easier, faster, higher-quality and more durable.”

Keene stated: “Moving from concrete to plywood substrates is a challenge. Wood bends and reacts quite differently than concrete, so extra care must be taken when installing an underlayment over wood. Since wood will bend under stress, the likelihood of a delamination increases. Some products are not designed to handle the different stresses presented by wood. Dependable recommends using gypsum products, for example, because gypsum is less likely to delaminate when going over wood.”

Stowell said that veteran contractors and installers should remain open to new technology designed to make their jobs easier. “Our synthetic gypsum AP and APF products can open doors and cover more critical substrates. Schönox products provide solutions for both concrete and wood substrates. If moisture is an issue then using moisture mitigation systems such as EPA Rapid will provide a fast solution.”

Fleury reiterated the importance of reviewing all instructions before starting. “A contractor may be familiar with the procedure of applying the material, but they must take the time to familiarize themselves with new products which may require an extra step, or better yet, allows them to skip a step like shot blasting. It is important to take the time to review each product’s instructions to make sure they are adhering to that specific manufacturer’s guidelines.”

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