Surface Preparation “The Foundation of a Successful Waterproofing Project”

A large percentage of issues on restoration and waterproofing projects can often be traced to improper evaluation and/or preparation of the concrete substrate.

Manufacturers disclose recommended surface preparation for their materials to achieve a long-lasting bond and the designed service life of the material. ICRI, and other organizations also provide guidelines and field tools to assist in both evaluating a concrete surface prior to installing a waterproofing or repair material and in achieving the proper level of surface preparation for a material.  To avoid costly and time-consuming problems after a material has been installed, it is important to evaluate the substrate, familiarize yourself with the material’s recommended preparation, and understand how to use industry surface preparation standards prior to installing or applying a material.

Evaluating the Substrate
Many issues can arise if a material is installed over a compromised, contaminated, or incompatible substrate.  It is important to always conduct a thorough evaluation of the surface.  For many projects this can be as simple as a visual inspection to look for surface cracks or possibly a physical “sounding” of the substrate to uncover areas of dis-bondment below the surface (Fig. 1).  Often, it may require more extensive testing to check for substrate deterioration, corrosion, or unsuitable moisture conditions. Both destructive and non-destructive methods can be used to undertake this evaluation.

ASTM C1583, Standard Test Method for Tensile Strength of Concrete Surfaces and the Bond Strength or Tensile Strength of Concrete Repair and Overlay Materials by Direct Tension outlines destructive testing protocols for determining the tensile strength of concrete surfaces and the bond/tensile strength of concrete repair and protective materials by pull-off testing.  (Fig. 2).

Non-Destructive methods can also be used to evaluate internal properties and conditions of sound, damaged, and repaired concrete with little or no damage to the structure. ICRI 210.4R-2021, Guide for Nondestructive Evaluation Methods for Condition Assessment, Repair, and Performance Monitoring of Concrete Structures, provides guidance on the selection of the most suitable nondestructive evaluation (NDE) methods for evaluating specific conditions relating to this assessment.

Cleaning the Concrete Surface
A thorough cleaning or de-greasing of the surface, if required, should be completed prior to employing mechanical preparation methods since many of these methods can spread surface contaminants to surrounding areas or in some cases, inject these contaminants deeper into the substrate.  A grinding disk can be contaminated by grease and oils and spread to adjacent areas.  Shotblast beads can also pick up contaminants and spread them across a concrete slab.

Surface Profile
One of the goals in performing surface preparation is to impart a profile to the surface.  Achieving this surface profile opens the pore structure of the concrete, increases overall surface area for a material to bond to, and provides an “anchor”.  As the substrate undergoes stresses such as thermal shock, impact, and abrasion, it imparts stress on the bond line of the repair or coating and the substrate.  If the surface does not have an adequate profile, these stresses can lead to loss of adhesion of a repair or delamination of the waterproof coating. These stresses vary from project to project so it is important to keep in mind that a level of preparation that works sufficiently on one project, may not be appropriate for the next project.  ICRI 310.2R-2013 Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, Polymer Overlays, and Concrete Repair is an industry recognized  guideline that includes levels of Concrete Surface Profiles (CSP) that can be used to evaluate the level of profile achieved on a substrate. 

Using the right tools for the job
Another important aspect of surface preparation is using the right methods and tools to achieve that preparation.  Many tools such as heavy impact or pulverization tools can damage the concrete surface by creating micro-fractures, otherwise known as “bruising” the surface.  These micro-fractures, if not removed, can weaken the substrate just below the bond line and lead to de-lamination of the repair area. ICRI 310.2R-2013 provides visual illustrations of this phenomena and steps to avoid this condition in the field.

Mock-Ups
One of the most effective ways to determine if the surface preparation employed is sufficient for a project is to conduct mock-ups that include some form of adhesion testing.  This allows surface preparation to be assessed under true project conditions. 

Conclusion
If the substrate is properly evaluated and prepared prior to the installation of a repair or waterproofing material, many issues can be avoided down the road.  Industry guidelines as well as material manufacturers data guides can be a good source of information to ensure these important steps are completed and the proper foundation is put in place for the repair.

Reference
ASTM C1583, Standard Test Method for Tensile Strength of Concrete Surfaces and the Bond Strength or Tensile Strength of Concrete Repair and Overlay Materials by Direct Tension (Pull-Off Method) ASTM International, West Conshohocken, PA, 2010.

ICRI 210.4R-2021 Guide for Nondestructive Evaluation Methods for Condition Assessment, Repair, and Performance Monitoring of Concrete Structures, International Concrete Repair Institute, St. Paul, MN, 2021.

ICRI 310.2R-2013, Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, Polymer Overlays, and Concrete Repair, International Concrete Repair Institute, St. Paul, MN, 2013.