✕

As tiling professionals, we all know that a flat sound surface is our best friend. We also know that these friends don’t come along very often without some rectification on our part. So crucial are even surfaces to successful installations that the Tile Council of North America (TCNA) Handbook has developed specific requirements for various types of installations.

To prevent installation failure for standard-size tiles with all edges shorter than 15 inches, the maximum allowable surface variation is 1/4 inch in 10 feet, with no more than 1/16-inch variation in 12 inches when measured from the high points in the surface. The requirements become more stringent for larger tiles. Installations of tiles with at least one side 15 inches or greater have a maximum allowable variation of 1/8 inch in 10 feet, with no more than 1/16-inch variation in 24 inches. Neglecting these requirements can lead to anything from installation damage to personal injury.

Grinding will bring down high spots and patching will bring up low spots to achieve this flatness. Depending on the size of the surface and severity of imperfection, these remedies can be time-consuming. There are even more extreme scenarios where an entire floor needs to be lifted to plane with another substrate. Enter self-leveling underlayments.

Tilers have been enjoying the wealth of benefits SLUs bring since they were first patented in 1997. | Photo courtesy of Merkrete

Tilers have been enjoying the wealth of benefits self-leveling underlayments (SLU) bring since they were first patented in 1997. A pourable pumpable cementitious product that works with gravity to seek its level holds enormous time and labor savings for flooring contractors. The product is so thoroughly effective and simple to use that the only changes to it in its quarter century on the market amount to how thick it can be applied in a single pour and amending its designation to “flowable hydraulic cement underlayment.” Effectiveness and simplicity aside, there are things to bear in mind when using SLUs.

SLU Musts

For a successful SLU pour, installers need to make sure they are working with a clean sound substrate. The substrate must be clear of oils, waxes, curing compounds, dust and other contaminants that can hinder the SLU bond. Cracks need to be patched or sealed. Once it is established that the substrate is ready to receive the SLU, it’s prime time. Always, always use a primer. A primer helps with the SLU’s flow, increases its bond strength and inhibits rapid water loss for a proper cure.

A primer helps with the SLU’s flow, increases its bond strength and inhibits rapid water loss for a proper cure. | Photo courtesy of Merkrete

Tilers also need to gauge the maximum thickness the SLU will need to be applied. Not All SLUs can accommodate the same thicknesses, so it is imperative to find a product designed to handle the project’s requirements. For example, some products can level up to 3/4 inch in a single pour. To achieve a thickness of 1 inch, installers will need a second pour after the first has completely cured.

Also, since SLU is a flowing product, tilers need to plug or dam areas they do not want SLU to go. Failing to do so can result in messy cleanup, possible grinding of cured misapplied SLU and even property damage. Spray insulation foam and edge strips are ideal products for preventing SLU seepage.

When the SLU is poured, tilers will need to use a gauge rake to move the product where it is needed. Breaking the surface tension with a trowel or spiked roller will help the SLU settle more evenly for a truly flat level surface. It will also alleviate any pinholes that can form while the SLU is curing. Once the SLU is applied, walk away until the product is dry.

Breaking the surface tension with a trowel or spiked roller will help the SLU settle more evenly for a truly flat level surface. | Photo courtesy of Merkrete

Not All SLUs Are Created Equal

The most crucial step installers need to follow is to follow manufacturers’ instructions for their products. SLUs tend to be the most difficult items tile-setting material manufacturers produce, painstakingly engineering the product to be as easy to use as possible. With that said, these products demand close adherence to their specific directions. Variations from product to product can include anything from water ratio to mixing method to how soon to pour after priming to when to start laying tile. It is essential to find a responsive manufacturer that will answer any question about their product in different flooring situations, as well as offers a comprehensive system warranty.