INSTALLING OVER CONCRETE

On new concrete subfloors, a minimum of 28 days curing is usually necessary before installing an underlayment. For most jobs, you can use the same tools required for overlay installation. You'll need a gauge rake to spread the material into place and to control the depth. Then you'll need a steel smoothing blade to level the surface and break the tension, allowing any entrapped air to escape.

You can place underlayments in thicknesses ranging from featheredge to 1 1/2 inches in one lift. It's even possible to achieve greater thicknesses where needed by extending the material with pea gravel (see Using Pea Gravel to Increase Thickness).

Spreading Underlayment Ardex Engineered Cements
You can place underlayments in thicknesses ranging
from featheredge to 1 1/2 inches in one lift. Using a gauge
rake to spread the material into place will help
to control the depth. – Ardex Engineered Cements

Pouring Underlayment Ardex Engineered Cements
An underlayment flows onto floor surfaces like thick pea
soup and requires minimal effort to smooth and level.
– Ardex Engineered Cements

Return to Concrete Underlayments
Concrete Floor Before Underlayment Ardex Engineered Cements
Just because an underlayment will be hidden under a floor
covering doesn't mean you can overlook surface preparation.
Before installing the underlayment, be sure to profile and prime
the floor and fill in any chips, gouges, or spalls with a suitable
repair material. – Ardex Engineered Cements
Using Pea Gravel to Increase Thickness

On one project I witnessed, a floor covering installer was trying to level a floor in preparation for vinyl tile. In some areas, there were capped-off drains approximately 3 to 4 inches below the finished floor elevation. The installer prepared the floor by shotblasting and priming, per the manufacturer's recommendations, and then dumped clean pea gravel directly onto the primed substrate, screeding it to a uniform thickness of about 2 inches. Then a crew pumped the underlayment over the bed of pea gravel while using a garden rake to blend the material in with the aggregate so it would filter down and come in contact with the concrete substrate.

I must admit that when I first saw this unusual approach, I was a bit skeptical. But after checking out the project over 3 years later, I found nothing wrong with the vinyl floor covering the top of the underlayment. If you plan to try this method, be sure to install a final leveling coat of the underlayment over the surface to smooth out any imperfections.

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