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The options for self-leveling underlayments (SLUs) are greater more than ever and it is sometimes complicated to choose the one that fits the best your need on a job. Should you look for drying time or compressive strengths? Should you look for a system or for a product only? Unfortunately, there is no simple answer to these questions and the solution always varies from a job to another. However, they are common criteria that help you to choose what you need.

There are four main things you should consider when selecting a SLU: thickness, flow, drying time and compressive strength.

There are four main things you should consider when selecting a SLU: thickness, flow, drying time and compressive strength. Photos courtesy of Sika (Click on image to enlarge.)

The market recognizes four technical criteria that can impact your decision:

Thickness

  • When working on a job and having flatness issues to fix, always check for the minimun thickness and the maximun thickness of the product you want to use. As of today, the market offers underlayment from ¹/₁₆ inch typically up to 3 inches. Typically, when a self-leveler can be applied thin, it has difficulties being applied very thick. The opposite can true as well: when a self-leveler can be applied very thick, the chemistry involves doesn’t allow thin thickness. Where is the happy medium? It is also interesting to ask for the thickness you can achieve with the addition of aggregate. You should also ask how many layers you can combine to achieve the thickness you want to obtain. Always ask as well if you need to use a primer between layers, and if so, if the primer has to be diluted or be used as is.

Flow

  • The flow of a self-leveler will determine the easiness of work on your job. The higher the flow is, the easier the self-leveler will place itself in the area. A high-flow product will go back to its place even if you work the product after being placed. In the meantime, the flow is important for the healing of the self-leveler. With a high-flow product, your crew won’t have to over work the product to achieve an even layer.

Drying Time

  • This is by far one of the most critical criteria. After how long can I walk on my self-leveler and after how long can I cover it up? Once again, the answer varies and this is why you have to select the underlayment that will allow you to achieve what you want. If you have a fast turnaround job, you will look for a rapid-drying self-leveler. Some of the products available on the market allow you to put down your floor covering in as little as 90 minutes. On the other hand, if time is not an issue, some self-levelers can take up to three days before you can lay down your floor. As of today, most of the self-levelers allow you to lay down your floor the day after. The difference of the drying time within the different leveler is mainly due to time it takes for the moisture to escape the product. As floors can be very sensitive to moisture, you have to pay attention to the manufacturer recommendation.

Compressive strength

  • It is obvious that the strength, which is required for a floor, is different if you are in a warehouse, a grocery shop, an office or a house. To follow this need, every self-leveler reaches a specific compressive strength. Today, you can find self-leveler going from 3,000 psi to more than 7,500 psi. The higher the compressive strength is, the more traffic and load the self-leveler can handle.
A level floor not only aids in a successful tile installation, but peace of mind for all parties involved.

A level floor not only aids in a successful tile installation, but peace of mind for all parties involved. Photos courtesy of Sika (Click on image to enlarge.)

On top of these four main criteria, you can find more specific solutions. For healthcare projects, you can use a low-dust self-leveler. This new and innovative technology prevents the dust from spreading around, which is a great feature in such sensitive environments. If you work over plywood, you can choose a lightweight, low-shrinkage or gypsum-based self-leveler; it will avoid reinforcing the plywood or sometimes, including a wire lath. You also have now some solutions suitable for the outside as these solutions won’t be affected by moisture.

One of the last thing to pay attention to when choosing the right product for your job is the primer coming along with it. No matter what product you use, primers are always mandatory:

  • On non-porous substrates to create the adhesion between the substrate and the self-leveler.
  • On porous substrate to prevent the moisture of the self-leveler to move to the substrate. It would create an inconsistency in the drying process of the self-leveler and will lead to a risk of failure. Not using a primer for porous substrate could also lead to the creation of pinholes.

When choosing your primer and self-leveler system, it is important to check the overall drying time, as some primers take 10 minutes to dry while others take three hours.

To wrap this up, when you have to choose a self-leveler for a new job, always ask yourself: “What do I want to achieve?” Are you looking for high thickness, great flow, fast-drying time or high compressive strength? Or maybe you’re looking for two out of these four criteria? The best solution is to have a self-leveler that offers a flexibility in thickness for your daily jobs and to have some more specifics products for more demanding jobs. A rapid-drying self-leveler is perfect for fast turnaround jobs such as grocery shops, while a low-dust solution is the best fit for healthcare projects. And don’t forget, manufacturers are here to help you choose your best fit.