Waterproofing breaches that lead to major structural restoration

by brittney_cutler_2 | October 1, 2021 12:00 am

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by Daniel Aleksov, P.Eng., BSS

When performing a walkthrough of a building and observing symptoms of degradation of the concrete structure one will certainly ask themselves “Why is this happening?” The short answer is the concrete was inadequately protected. Concrete is a durable material that has stood the test of time, but in the modern age, it has a fundamental weakness that depends on how it is reinforced. Ironically, the steel used to increase concrete’s tensile strength is also its weakness when it is subject to attack from foreign contaminants such as water, oxygen, carbon dioxide, chlorides, and aggressive chemicals.

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These foreign contaminants induce steel corrosion which is the leading cause of concrete deterioration. Although concrete naturally protects the embedded steel, it has its vulnerabilities due to its porous nature and is susceptible to cracking when it undergoes volume changes. Cracks, joints, and penetrations coupled with unprotected concrete are a path of least resistance for moisture along with the other contaminants to reach the embedded steel. As the steel corrodes over time, it increases in volume and exerts pressure on the surrounding concrete which leads to delamination (separation of concrete layers) and spalling (detaching from the structure itself).

All these symptoms are indications the concrete is in distress and requires immediate attention. The corrosion and section loss of the steel jeopardizes the load-carrying capacity of the concrete and has the potential to lead to catastrophic failure if measures are not taken to temporarily support and rehabilitate the structure. This is why it has been understood for well over 50 years that concrete requires protection and the concept of a waterproofing barrier system was developed.

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Protecting structural components from water penetration

A waterproofing barrier is a combination of systems and materials designed to resist hydrostatic pressure exerted by moisture in a liquid state. Its sole purpose is to protect the structural components from water penetration and, by extension, into a usable space. To have a successful barrier, it must be continuous from slab to walls and other surfaces subject to liquid moisture. Waterproofing barriers traditionally consisted of multiple layers of bituminous saturated felt bonded together with hot applied coal tar pitch or asphalt. Currently, hot applied rubberized asphalt membranes are still commonly installed, but there is a vast array of other waterproofing barrier types used such as cold applied rubberized asphalt, elastomeric thin system membranes, cementitious coatings, modified bituminous asphalt, polyvinyl chloride (PVC), bentonite clay, etc. The focus of this article will be on fluid applied waterproofing membranes primarily on horizontal portions of traffic surfaces.

The five most common types of waterproofing breaches for liquid applied membranes are as follows:

1. Pinholing is a phenomenon that occurs when trapped air outgasses from the waterproofing coating creating bubbles that burst and leave behind small craters. Some of the causes of this condition include but are not limited to a porous or uneven concrete surface, dampness, direct sunlight, insufficient primer application, and a high ambient or substrate temperature. Following the waterproofing membrane manufacturer’s application instructions is essential to avoid this type of issue with respect to surface preparation, primer coverage rates, temperature, and humidity ranges as well as environmental conditions conducive to proper curing.
2. Wrinkling occurs in the form of bubbling when water penetrates and migrates below the membrane or is absorbed from the concrete. That is why it is imperative for the concrete substrate to be within acceptable limits with respect to moisture content.

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Verification of moisture content can be performed by various methods including the plastic sheet method or a handheld moisture meter. However, in colder weather, when there is limited vapour drive, an in-situ probe should be used to obtain a more accurate reading.

It is also important to understand if the substrate consists of a hollow core slab or composite metal deck which will require venting to allow the moisture to dissipate. Wrinkling can also develop during the installation of elastomeric reinforcing sheets during hot-applied rubberized asphalt which will create a tunnel-like opening at the seams for water to penetrate. This condition is also common for sheet-applied waterproofing membranes that rely on fusing two adjoining rolls of the membrane at side and end laps.

3. Blistering is a type of breach that occurs when liquid-applied polyurethane membrane layers are applied too thick causing the coating to become spongy and soft. Exceeding the manufacturer’s design thickness requirements, using the wrong tools, as well as having a very rough concrete surface profile can cause this to happen.

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During membrane installation, it is important to perform quality control measures such as measuring the wet film thickness. Any depressed or rough areas should be filled prior to membrane application. Larger blisters can also form from moisture migration which originates from the concrete having a high moisture content.

4. Splitting develops when the waterproofing system cracks due to excessive movement beyond its elongation capability. Inadequate detailing of cracks or construction joints, excessive slab movement due to thermal effects or slab deflection, as well as a thicker-applied coating (polyurethane systems) are the leading causes of this type of failure. The type of crack treatment will depend on crack widths encountered following surface preparation of the concrete substrate.

Cracks with widths less than 1.6 mm (0.0625 in.) will require a detail coat of waterproofing membrane above the crack prior to the entire base coat application. When cracks exceed 1.6 mm then it is industry standard practice to rout and seal the crack with sealant followed by a detail coat. For rubberized asphalt waterproofing, different reinforcements are used in conjunction with detail coats based on the crack width criteria.

For larger movement joints such as those that are classified as expansion joints, this requires even more careful attention to detail to ensure splitting does not occur. Waterproofing is engineered and tested to an optimal thickness to produce the desired elongation capability. Excessive thicknesses during waterproofing membrane application can create a more rigid system which reduces the waterproofing’s capability to bridge cracks effectively.

5. Delamination is an indication the waterproofing membrane is poorly bonded to the concrete substrate and has peeled off or is at high risk to occur. Areas of exposed concrete and peeled-off waterproofing coatings can be easily identified visually. However, other areas may appear sound visually but may be completely debonded.

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On exposed traffic waterproofing coatings, this can be detected by chain dragging the top surface which is a non-destructive method by acoustic sounding. Another method of assessing the bond of the waterproofing membrane is by performing a test cut and verifying the adhesion qualitatively.

For elastomeric traffic waterproofing coatings, adhesion tests can also be completed with a portable device that can measure quantitatively the pull of strength (bond strength). This breach can originate due to inadequate surface preparation, moisture, contaminated slab, insufficient membrane thickness, damage from vehicle impact, and chemical exposure. To avoid delamination and achieve a good mechanical bond, surface preparation by abrasive blast cleaning (shot blasting) is recommended to obtain a concrete surface profile of three to four.

Once the prep is completed, it is imperative the concrete substrate is clean and dry as per the manufacturer’s specified requirements to facilitate a good adhesive chemical bond. Proper application in terms of thickness and coverage of all waterproofing components including primer, base coat, and topcoat will impact the bond. Curing is also an important factor that should not be overlooked as inter-coat adhesion can also be affected if one of the components does not fully cure.

The performance of the waterproofing system during its entire useful service life will be dependant on factors such as design, workmanship, assessment, maintenance, and repairs. Upon closer examination of these factors, one gains a deeper understanding of how the integrity of the waterproofing is undermined and how the structural components are affected.

Design

The design methodology has a significant impact on the overall outcome of the waterproofing performance beyond adhering to minimum code requirements. Here are some common questions to consider during th

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e preliminary design stage:

 

• Does the below grade surrounding area have a high-water table or is the area prone to flooding?

• Are the materials selected durable and suitable for the specific application?

• Are there penetrations and sections of the expansion joint directly above critical infrastructure?

• Do the floor slabs and foundation walls have enough provisions for drainage?

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Without considering these types of questions, the designer can create vulnerabilities once the project is initiated. Locations and detailing of expansion joints and other types of penetrations such as drains is critical since these areas are the most susceptible to failure of the waterproofing systems. During many garage condition assessments completed, one will commonly observe concrete ledge beams supporting the intermediate slab experiencing delaminated concrete due to premature failure of the expansion joint waterproofing. Delaminated concrete can develop as early as five to 10 years following a breach in the water barrier. As the structural elements age and the waterproofing membrane approaches its end of useful service life, the concrete deterioration can be quite significant if the structural elements were exposed to consistent water and foreign contaminant ingress over extended periods of time.

Workmanship

This factor is determined on how the design is executed by the contractor from a workmanship perspective as well as the quality control measures implemented during construction. Deviation from a sound design or by ignoring standard waterproofing installation standards and procedures can also lead to premature failure. Misguided practices include, but are not limited to, improper concrete surface preparation, a high moisture content on the concrete slab surface, or not following application procedures from the manufacturer which include mixing of material, curing, application temperature, thicknesses, etc.

Throughout the author’s entire career, he has only seen two garage roof slabs to wall junctions with missing waterproofing. The absence of proper waterproofing on below grade walls and slabs is a huge risk and one of the major factors that contributed to the collapse of the Algo Centre Mall roof located at Elliot Lake in 2012 according to the forensic engineering report.

Assessment

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Underground parking garage and basement condition assessments should be performed by licensed professional engineers with experience in identifying problems early on such as water penetration at walls, slabs, expansion joints, concrete deterioration, drainage issues, etc. A condition assessment report should include quantified observations, conclusions, and recommendations for repairs complete with budget estimates.

Unfortunately, many building owners request a condition assessment far too late after the waterproofing membrane breaches have caused significant deterioration to the concrete. The only way to stop this from reoccurring is to legislate mandatory structural condition assessments for underground parking garages in Ontario every three to five years as enacted by New York State and Quebec, respectively. Further, if any structural concerns and remedial repairs are communicated to the building owners, there should be an enforcement strategy to ensure the deficiencies outlined are addressed within a specified timeframe.

Recently, a 98-year-old detached house was undergoing basement renovations and the contractor discovered major sub floor damage which was caused by water penetration from the exterior concrete block foundation wall. The wall was observed to be protruding 50 to 75 mm (2 to 3 in.) out of plane likely from frost.

This is a very serious condition with potential for the foundation wall to catastrophically collapse. Emergency shoring has been installed and the wall was completely replaced with new waterproofing and drainage installed along the entire length of the wall elevation.

Maintenance

The minimum maintenance standards involve annual reviews by building staff ensuring the slabs’ drains are free of debris and vehicle traffic waterproofing systems are cleaned on a regular basis. Part of this review should include accessing the hydro vault to ensure there is no evidence of water penetration which could cause a potential fire or explosion.

Localized repairs and replacement of worn and debonded membranes should be addressed as part of a maintenance plan to avoid leaving the concrete unprotected and exposed to water and de-icing salts which can lead to corrosion of the embedded reinforcing steel. The Canadian Standards Association (CSA) 413, Parking Structures, under Annex E.1, routine maintenance clearly states, “the cost of repairs to protection systems is a small fraction of the cost of repairing consequential damage to the structure.” Based on practical experience, the average cost difference to repair the structure is a minimum of 10 times the cost to repair the waterproofing system.

Repairs

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Full replacement of waterproofing membranes at the end of their service life is inevitable and requires diligent financial planning since these types of projects can be quite costly when major structural restoration is involved. Depending on the first four factors, this can have a tremendous impact to the service life of the waterproofing and the repair strategy. For the waterproofing system to perform to its maximum potential, action needs to be taken promptly when problems initially occur.

References

American Concrete Institute (ACI) 515.1R “A Guide for the Use of Waterproofing, Dampproofing, Protective, and Decorative Barrier Systems for Concrete”

• Canadian Standards Association (CSA) S413-07, Parking Structures

• International Concrete Repair Institute (ICRI) Guideline No. 310.2R-2013, “Selecting and Specifying Concrete Surface Preparation for Sealers, Coating, Polymer Overlays, and Concrete Repair”

• ICRI Guideline 710.2-2014, “Guide for Horizontal Waterproofing of Traffic Surfaces”

[11]Daniel Aleksov, P.Eng., BSS is a principal and co-founder of Leading Edge Building Engineers and a senior structural engineer specialized in the restoration and renewal of existing buildings. He has spent more than a decade assisting building owners and property managers solve water penetration and building component failures with durable and cost-effective solutions. At Leading Edge, he is responsible for all technical aspects of building envelope and structural restoration projects from the initial assessment phase to the design and construction completion. He has successfully completed more than 300 engineering projects related to underground parking garages, site works, landscaping, windows, walls, sealants, roofs, balconies, plumbing and HVAC. Over the last five years, Aleksov has been cultivating his creativity which has helped him develop his own quality control tool and use new technology such as drones and wireless concrete sensors for building applications. He has also contributed valuable insights on social media as well as shared perceptive and thoughtful presentations with all stakeholders in the industry. He is an active member with many professional organizations and serves as a board of director for the Ontario Building Envelope Council (OBEC) and chairs the communication committee. He is also involved with the International Concrete Repair Institute (ICRI) and volunteers for the concrete repair and waterproofing committees. He is committed to lifelong learning and creating a positive impact to the engineering and construction industries.

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