The Manual of Below-Grade Waterproofing

Justin Henshell

• Publisher: Routledge
• Year: 2016
• ISBN:
  9781317211884
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Construction & Architectural Engineering
• Index: Technology & Engineering

The ever evolving technology of waterproofing presents challenges and risks for architects and engineers who do not specialize in the field. The revised edition of The Manual of Below-Grade Waterproofing Systems provides the education and product information to enable designers to take a sound, fundamental approach to these contemporary challenges.

Building designers specify waterproofing systems and materials that are often based on limited and subjective manufacturers' literature or past experience with systems that work under specific conditions, but will fail in other installations. Leakage usually leads to litigation. This book gives you the tools to prevent that.

This manual covers the history and science of waterproofing materials, the considerable distinctions between waterproofing roofs and plazas and below-grade surfaces, the critical procedures for protecting waterproofing materials during construction, diagnosing and remediating leaks, writing specifications, and detailing waterproofing components. The pros and cons of every waterproofing material and system are comprehensively covered. You will learn how to:

• weigh positive- versus negative-side waterproofing systems

• weigh dampproofing versus waterproofing

• coordinate with all the professionals in the waterproofing delivery chain

• follow environmental protection and government regulations

This book is an essential resource for architects, civil engineers, contractors, designers, materials manufacturers, and all other professionals involved with the design and construction of underground spaces.

1 Introduction

A. What is waterproofing?

In this manual, in accordance with ASTM usage, waterproofing means a system designed to resist hydrostatic pressure exerted by moisture in a liquid state. It is differentiated from dampproofing, which is designed merely to resist the flow of moisture in a gaseous state (i.e., water vapor). See Chapter 3 “Dampproofing,” and Chapter 5 “Waterproofing,” for a detailed explanation of this distinction.

Waterproofing is often erroneously defined as a coating applied to above-grade masonry or concrete walls; a membrane cover on spandrel beams; a membrane in split-slab construction under a mechanical or shower room; a coating on a parking garage, in a tank, or pool; as well as four different treatments of below-grade foundation walls and slabs.

A subtler source of semantic confusion is distinguishing between a waterproofing system and a low-slope roof system when the roof system is a so-called Protected Membrane Roof (PMR) assembly. In a PMR, the membrane is placed directly on the deck below the insulation, instead of in its conventional, weather-exposed location atop the insulation. When a PMR is ballasted with concrete pavers, it resembles a waterproofed plaza. A roof plaza can, in fact, be identical to a waterproofed plaza at or below grade.

The distinguishing feature differentiating a PMR from a waterproofed plaza system is the accessibility of the membranes in the event of failure. This feature is the basic determinant of manufacturers’ willingness to issue guarantees. Manufacturers will generally guarantee a PMR if pavers are installed on pedestals, in which case the membrane is accessible. Most manufacturers will guarantee PMR systems in which pavers, serving as ballast or maintenance walkways, are loose-laid on the insulation. (In industry semantics, such a system is not considered to be plaza waterproofing.) If, on the other hand, the membrane is inaccessible – with wearing surface-units (such as brick, tile, or stone) installed in a mortar setting bed or in sand over a concrete protection slab – then the system is classified as waterproofing, and manufacturers will not guarantee it.

A guarantee should, however, be a secondary consideration. You should select a PMR system only if your primary goal is to provide a client with the dubious assurance of a manufacturer’s warranty. If a lower-risk system assuring long service life in a continuously moist environment over a moisture-sensitive space is your primary goal, then a waterproofing system is a more prudent selection.

Another source of semantic confusion is distinguishing between a below-grade waterproofing system and a plaza waterproofing system. Though both are used below grade, very few plaza waterproofing systems are designed to resist significant hydrostatic pressure.

B. Using this manual

You do not need to read this manual cover-to-cover to gain practical guidance. The table of contents and index (or keyword search, if you are reading an eBook edition) should direct you to the material that will help with your current need. Each chapter covers individual waterproofing topics in depth. Cross-references are provided within chapters to direct you to additional relevant material.

The objective of the manual is to help you avoid waterproofing system failures. Manufacturers of roof waterproofing systems provide considerably more selection, design, and installation support than manufacturers of below-grade waterproofing systems do. This manual is dedicated filling that gap as well as providing a sound, fundamental approach to waterproofing problems.

C. Manual’s scope and limitations

This manual focuses on waterproofing of below-grade, habitable building spaces subject to hydrostatic pressure, as well as dampproofing. It is therefore limited to covering waterproofing and dampproofing for the following underground building components:

• structural concrete slabs with a wearing surface or earth fill;

• concrete slabs-on-ground below-grade elevation; and

• foundation walls.

Waterproofing (and dampproofing) for the following structures are not covered:

• water-containment vessels;

• vehicular, pipe and similar tunnels not enclosing habitable space;

• above-grade mechanical room floors (not exposed to groundwater or soil chemicals);

• traffic toppings or traffic-bearing waterproofing systems for vehicles and balconies offering short-term protection, but not resistance to hydrostatic pressure; and

• green vegetative roofs.

This manual is not a substitute for the professional expertise required to design a waterproofing system. It illustrates general design principles. As most waterproofing projects have unique aspects, you will not simply be able to copy details provided here. You will need to adapt them to your project. In some cases, details provided by manufacturers will be more relevant than the general details included in Chapter 17.

Because waterproofing technology is rapidly changing, some systems presented herein may be obsolete or superseded by others as you read this.

D. The importance of waterproofing

Urban planning critics, who discuss the purely architectural aspects of plaza design with informed expertise, normally ignore the functional aspect: The unseen waterproofing system required to sustain these aesthetic triumphs. Space under the street-level plaza, located on prime land sometimes priced at four digits per square foot, is inevitably dedicated to high-level occupancies in which the slightest leakage is intolerable.

A waterproofing system should ideally last the full service life of the building. Thus, durability is the first principle of waterproofing design. Most building systems can be designed for service lives far short of projected building service life. Air-conditioning equipment, lighting, office partitions, communications, even elevators, curtain walls, and roofs can be designed for anticipated replacement as they either become obsolete or wear out under constant weathering. A waterproofing system, however, is like a foundation and structural framework in its need for endurance.

The importance of durability is illustrated by industry practices. Few waterproofing manufacturers offer guarantees or useful warranties, yet manufacturers usually do support roofing materials. The few warranties available are for severely limited liability, for two major reasons:

1. Waterproofing for foundations and under slabs-on-ground is often inaccessible.

2. Replacement of waterproofing systems under plazas may require removal and replacement of tons of overburden or jackhammering removal of concrete protection slabs and concrete topping.

Such drastic remedial action sometimes costs more than 300 times the membrane’s cost. That risk motivates prudent designers to ignore first-cost economy when it entails any risk of failure. Prudent designers select systems and materials that will work, regardless of a few dimes per square foot cost increase. They also require:

• approved applicators for installing waterproofing systems;

• rigorous quality assurance (QA) inspection programs during installation; and

• flood-testing, whenever practicable.

While the problems of modern waterproofing have multiplied, advances in waterproofing technology have multiplied at an even faster rate, giving you a vastly expanded selection of new systems and materials. Modern polymer chemistry expands your arsenal of weapons against leakage while complicating the problem of selecting the proper combination of systems or materials.

E. The boom in demand for waterproofing

The growing demand for a greater quantity and higher quality of waterproofing in building construction has a simple explanation. The rapid proliferation of air-conditioning following World War II made windowless underground spaces feasible for human occupancy. Before that, underground spaces were severely limited by the practical inability to control interior temperature, humidity, and circulating air quality for comfortable, healthy habitation. The advent of air-conditioning created a demand promoted by many interrelated factors:

• space needs for expanded mechanical plants

• space needs for windowless functions

• trend toward water-shedding curtain walls

• sites with poor drainage

• incentive zoning for open, street-level plazas

• rise in HVAC energy costs

• rising cost of waterproofing failures

Space needs for expanded mechanical plants grew with the demand for sophisticated HVAC systems, electronic data processing centers, and other new technologies in the postwar building boom. The rudimentary building mechanical equipment preceding the 1950s seldom required deep basements. Huge chillers and other mechanical equipment for office skyscrapers created a demand for more underground space. Basements, sub-basements, and even sub-sub-basements were excavated to accommodate this equipment (see Figure 1.1).

Space needs for windowless functions include many functions best conducted in an environment usually isolated from the outside world. As underground locations are necessarily windowless, they are prime locations for a broad spectrum of occupancies: theaters and similar audio-visual uses, archives, mainframe computers, electronic switch gear, parking, retailing, and bowling alleys.

Figure 1.1 This deep excavation, for the New Academic Building at Cooper Union in New York, provided spaces for an auditorium and laboratories below grade where daylight was unnecessary. The groundwater level was 12 feet above the basement floor

The trend toward water-shedding curtain walls aggravated building waterproofing problems. The traditional masonry walls of pre-World War II construction absorbed substantial quantities of rainwater and shed it by evaporation in a cyclical wetting-drying process. Glass and metal wall panels shed this water rapidly via vertical flow directly to the foundation soil. Accumulation of storm water at the foundation thus magnifies drainage and waterproofing problems at the building basement.

Sites with poor drainage became more common during the 1950s when the accelerated tempo of postwar building made prime land scarcer. Foundation soil at previously occupied sites was sometimes contaminated, particularly in reclaimed swamps. Contaminants included acid and alkaline water, insecticides, soil poisoners, and fertilizers and petroleum products discharged from vessels, refineries, and underground tanks.

Zoning regulations promulgated to induce developers to provide more open space in city centers, magnified waterproofing problems. Incentive zoning offered developers greater building heights and floor area in return for street-level plazas. To maximize the economic potential of high-priced urban land, underground commercial space and parking garages were built below these plazas. Waterproofing of these city-center plazas requires much greater dependability and durability than traditional membrane waterproofing of sidewalk vaults over cellar utility spaces.

The energy crises of the 1970s indirectly complicated waterproofing design. Prior to the sudden increases in energy costs, when heating oil cost less than 10 cents per gallon, thermal insulation was invariably omitted from waterproofing systems. Earth-covered buildings, which enjoyed a brief vogue in the early 1970s, are more energy-efficient than conventional, above-ground buildings. Increasing the underground space in a conventional building increases the overall energy efficiency of the building, but presents a tougher waterproofing problem.

Rising costs of waterproofing failures have accompanied modern building trends. Failure may occur even without leakage of liquid moisture into the occupied space. Environmentally sensitive occupancies are routinely located underground in contemporary buildings. Electronic equipment in underground computer rooms and public assembly spaces containing audio-visual equipment require rigorous humidity control as well as leakproof waterproofing. Auditoriums with wood floors are nearly as demanding as computer rooms. Such uses create unprecedented waterproofing problems.

F. Historical background

Paradoxically, the archetypal waterproofing project, the Hanging Gardens of Babylon, anticipated modern waterproofing problems nearly 26 centuries ago, six centuries before the Christian era. One of the seven wonders of the ancient world, the Hanging Gardens featured terraces rising 75 feet from a colonnade superstructure. Waterproofing consisted of bitumen and lead. Along with other plants, trees were planted in the overburden over the earth-covered deck and watered by slave-powered irrigation machines lifting water from the nearby Euphrates (see Figure 1.2).

By the beginning of the twentieth century, waterproofing projects involved more mundane uses, primarily tunnels, dams, pools, and other water-containment structures. Cellar vaults under sidewalks were also protected, normally with built-up coal tar pitch membranes. These early built-up bituminous waterproofing membranes comprised alternate layers of cotton or burlap, organic felts, and coal tar pitch. Membranes were then covered with bricks dipped in hot pitch. Before World War I, b...