Concrete Porosity: The Immense Impact on Flooring Installation

By Bill Luallen, National Sales Director, XL North

It’s important to understand the necessity, and benefits, of rendering concrete substrates porous before installing resilient flooring.

Porosity of a Concrete Substrate Affects:

  1. Flooring adhesives – More porous substrates take less time for an adhesive to dry/cure. Installers can lay into the adhesive wet, semi-wet, or dry. Less porous substrates take longer for an adhesive to dry/cure, and limit the type of flooring installations. Installers can lay into the adhesive dry, using a pressure sensitive adhesive.
  2. Concrete sealers – Blocks pores. Moisture from concrete substrates cannot permeate the surface or flooring. Higher porous concrete creates stronger bonds between sealers and substrates. Flooring adhesive can be applied to the sealer, then resilient flooring product over the adhesive.
  3. Cement based underlayment – Coats/covers concrete substrates to achieve industry acceptable substrate flatness specification. Flooring adhesive is applied to underlayment, then resilient flooring product over the adhesive.
  4. Concrete primers – Primers neutralize the pH of lightweight concrete substrates, rendering them less porous. Primer increases bonding characteristics, spread rates, and drying times of the products being applied. Flooring adhesive can be applied to the primer, then the resilient flooring product over the adhesive.

Time is Money

Longer times for desired porosity and drying means contractors lose money waiting to install the flooring. With the area not in service, the owner also loses money. Adhesives, sealers, and primers take longer to dry over non-porous substrates, and the bond may be degraded.

Effects on Mixing Concrete

Concrete is naturally porous. Invisible pores constitute 12 – 18% or more of the concrete. The “water to cement ratio” is the most crucial factor. Concrete should be as dense and non-porous as possible. When it is less porous, its strength increases. This is called “compressive strength”. The mix is easier to place with more water. About half of the water needs to evaporate after the concrete is poured. When the surplus of water pushes to the surface, a network of capillary pores appear in the concrete. When concrete is mixed and poured, air becomes trapped in the mix, causing the finished slab to contain air voids which can fill up with water. Many methods of minimizing pores are detrimental to floor covering installations. The use of a concrete vibrator and over troweling are two easier, cheaper methods to clear out air and pores, but these work against the application of most products. The bond of most products applied to these slabs is inferior.

ASTM F3191-16, Standard Practice for Field Determination of Substrate Water Absorption

(Porosity) for Substrates to Receive Resilient Flooring.


  1. In order to properly install flooring adhesives, cement-based underlayment, primers, and other products, it is essential to know how porous a substrate’s surface is.
  2. Because of porosity’s direct effect on these crucial factors, many product manufacturers reference the criteria in their application instructions.
  3. A number of industry publications have also made note of the standards, including CRI’s Carpet Installation Standard, RFCI’s Recommended Installation Practice for Homogenous Sheet Flooring, and Fully-Adhered.


Use of ASTM F3191-16:

Test for porosity by placing 0.05 ml bead of water on the concrete’s surface to observe absorption. If water is not absorbed within one minute, the floor is considered non-porous. Non-porous concrete surfaces are generally rendered porous by mechanically abrading the concrete’s surface.

Moisture Testing

Concrete substrate moisture and pH testing must always be performed on concrete substrates on every grade level. Moisture testing is specified to be performed using the latest versions of the following methods:

  1. ASTM F2170 – In-situ relative humidity test measures internal humidity in the concrete. A ‘resilient’ product manufacturer and/or adhesive manufacturer sets the RH % moisture specification/limits for specified products.
  2. ASTM F2659 – Tests substrate surface moisture by using an electronic impedance moisture meter. A ‘resilient’ product manufacturer and/or adhesive manufacturer sets the RH % moisture specification/limits for specified products.


The Concrete Surface Profile (CSP) Scale

To achieve proper porosity in the past, as per ASTM F3191-16, the surface was typically mechanically abraded to receive one of the previously mentioned flooring products. This method is costly and messy. There have been significant improvements of these methods. There is some debate over what Concrete Surface Profile (CSP) is needed to achieve proper bond and porosity.

The CSP scale:

  1. Defines the texture of the surface of the concrete substrate. In the past, the texture of the surface has been related to how porous the concrete was.
  2. Goes from 1-10. 1 is the least textured, and 10 is the most textured.


Most manufactures require a 1-3 CSP when applying the above-mentioned products to a concrete substrate. However, it has been found that a CSP of 1 is more than enough to achieve proper porosity when using the right method.

Best Method for Achieving Porosity

Proper porosity and profiling methods are equally important for installations. XL North’s new product, Porosity+, achieves desired porosity quickly, with minimal effort.


  1. profiling concrete creates zero dust from diamond grinding
  2. no changing sanding pads
  3. shortens entire process
  4. adds quality
  5. adds profitability

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