ince the beginning of human history, people have been building shelter to pro-

tect themselves from the environment. Human intuition would suggest that

nothing beats a warm, dry bed. Intuition would also suggest that rain and

water belong on the outside of a building, not the inside.

Building design and materials have advanced greatly over time.

Construction materials such as concrete allow designers to create more

than just shelter, but buildings that deliver much more in the form of

durable, economic, aesthetically pleasing buildings. As greatly as build-

ing styles have varied over the years, one objective has remained con-

10 J o u r n a l o f A r c h i t e c t u r a l C o a t i n g s / J u n e / J u l y 2 0 0 8

Putting a hold on leaks

SSlamming the watergate: Proper selectionand use of coatings,sealants serve a central rolein shoring up the integrityof the building envelope

By Christopher Perego,BASF Construction Chemicals-Building Systems

Photo courtesy of Kellie L. Folkerts

spalls; loose rail posts; peeling paint;

and efflorescence. Depending on the

nature of the building design, concrete

spalls and loose rail posts on balconies

become serious public-safety issues and

a significant liability for the building

owner.

There is a saying in the construction

industry that goes, “Last on, first

called.” This generally refers to the last

contractor to work on the exterior of

the building. Often, this is the painting

contractor. Concrete buildings can leak

for many reasons; the wall coating is

only one of these reasons. The list of

potential issues is expanded by the vari-

ous types of building design and mate-

rials. This article will focus on some of

the most common issues related to

moisture protection for concrete build-

ings.

Moisture protection for concrete

structures constitutes a broad topic and

stant: the objective of keeping water

out of buildings.

Concrete in all its forms (cast in

place, precast, tilt wall) generally per-

forms well in the face of moisture; how-

ever, concrete represents only one com-

ponent of the building envelope. While

concrete participates with other materi-

als to provide a protective skin for the

structure, the concrete itself needs to be

protected from the effects of moisture.

A building envelope is comprised of a

variety of materials working together as

a system to protect indoor environ-

ments from the elements—rain, snow,

and warm or cold air. Unwanted mois-

ture in a building can lead to a multi-

tude of problems: water damage to the

building and its contents; mold; poor

indoor air quality; peeling paint; and

damaged finishes. The implications for

the exterior can be just as serious: cor-

rosion of reinforcing steel; concrete

can encompass the entire building from

the footing to the roof system. This dis-

cussion will focus on three areas.

• Common problems related to sealant

preparation and installation;

• Proper coating selection and applica-

tion; and

• Common design- and construction-

related issues that affect a building’s

protection against moisture.

Elastomeric sealantsSealant technology has advanced over

the years, but its primary purpose

remains the same: to prevent the pas-

sage of air and moisture. The sealant

plays a vital role in protecting a build-

ing from the ingress of moisture.

In the construction community, the

terms “sealant” and “caulk” are used

interchangeably. While both types of

materials are used to prevent the pas-

sage of air and moisture, sealants are

12 J o u r n a l o f A r c h i t e c t u r a l C o a t i n g s / J u n e / J u l y 2 0 0 8

generally designed to accommodate

differential movement greater than

25%. Caulks are mainly used for aes-

thetic and sanitary applications. For

the purpose of this discussion, sealants

will be the focus.

Sealants are used in numerous loca-

tions of the building envelope, such as

the following.

• At expansion joints, for control of

expansion and contraction

• Where dissimilar materials meet,

such as EIFS and concrete

• On window and door perimeters,

where they provide a weather seal

around windows and doors

• On parapet caps, where they prevent

wind-driven rain from entering under

the cap

• At penetrations created by pipes,

conduit, anchorage, and signage

Differential movement occurs in

areas where materials of different types

meet on a wall. Movement also occurs

due to the expansion and contraction

of materials such as concrete. Because

the primary function of a sealant is to

accommodate differential movement, it

is important to know and understand

the potential movement of the joint.

The Sealant, Waterproofing &

Restoration Institute (SWR Institute)

provides reference information to help

the specifier determine the proper size

and spacing of expansion joints.1

Best practice dictates that the width

of an expansion joint should be four

times the anticipated movement.2,3

This design creates a safety factor for

joint performance and construction

erection tolerances.

Sealant failure in expansion joints is

a primary source of moisture infiltra-

tion in concrete structures. When

selecting a sealant, attention should be

given to movement capability and the

following factors.

Type of substrate. Buildingenvelopes are composed of multiple

materials. Thus, the ability to join dis-similar materials is an important

attribute of a sealant. Also, substrates

low in tensile strength, such as EIFS,

require low-modulus sealants, which

reduce bond-line stress, minimizing

failures.

Compatibility with residualsealant. Residual sealant is a reality inmost restoration projects, so the

replacement sealant should be compat-

ible with any residual sealant. With a

few exceptions, it is best to replace

sealant with the same technology.

Paintability. Elastomeric sealantsmove more than most paints and coat-

ings. Peeling paint over a sealant can

lead to further coating delamination,

resulting in damage to the concrete.

Selecting a sealant that is paintable

minimizes the risk of failure.

Sealant preparationand installation

It is widely accepted in the waterproof-

ing industry that the most critical fac-

tor in sealant application and the most

common cause of sealant failure is

joint preparation.

Preparation will vary slightly by sub-

strate, but the basic requirements

include the need for a clean, dry, and

sound surface. Implicit in this defini-

tion of “clean” is a condition that is

free of contaminants. Contaminants

such as dirt, oil, and asphalt can be

introduced during the cleaning process.

Care should be taken to avoid these

contaminants, as they will adversely

affect the performance of sealants.

The three most common methods of

joint preparation involve the use of

compressed air, the solvent wipe, and

mechanical preparation. Adhesive fail-

ure is often traced back to improper

cleaning of the joint. The following are

some common pitfalls of preparation,

along with recommendations to pre-

vent problems.

Compressed air. Air should be freeof oil and water; an oil filter and mois-

ture trap should be used to eliminate

contaminants. Oil introduced into the

joint will affect adhesion, and moisture

introduced to the joint will affect cur-

ing of most sealants.

Solvent wipe. This process consistsof wiping the joint with solvent. The

SWR Institute recommends the “two-

rag method,” with the use of clean sol-

vent and frequent changing of rags to

avoid spreading of contaminants in the

joint. The sealant manufacturer should

be consulted for recommendations on

solvents used to clean joints.

Mechanical methods. Theseinclude wire brushing, blasting, grind-

ing, and sawing, and are often the best

way to completely remove sealant

residue. Again, care should be taken to

avoid spreading contaminants through-

out the joint. Mechanical preparation,

however, is not appropriate for all sub-

strates and can void manufacturers’

warranties on window and door frames

and coated metal panels.

Example of coating that is not compatible withelastomeric sealant. Photos courtesy of BASF

Construction Chemicals-Building Systems.

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Only if the paint is tinted with low-VOC Colanyl® 500.

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Protective wall coatingsThe building envelope of most concrete

buildings is considered a barrier wall.

The exterior face of the building,

including seals, sealants, and wall coat-

ings, is designed to prevent the ingress

of moisture. We have discussed the role

of the sealant in a barrier wall system. A

protective wall coating also plays an

important role in preventing moisture

ingress and protecting the integrity of

the concrete structure.

At the same time it prevents moisture

from getting into the substrate, a pro-

tective wall coating must also allow

moisture within the substrate to

escape.4 A coating functions much in

the same way our skin functions: it is

waterproof while still allowing our bod-

ies to perspire.

The ability of a coating to allow mois-

ture vapor to pass is called permeability.

Vapor permeability is an important

issue that deserves and receives consid-

erable attention, but we will leave that

discussion for another forum.

Permeability is only one of several

important properties to consider when

selecting a coating.

The most common

source of coating fail-

ure on concrete build-

ings can be traced to

erroneous material

selection—selecting a

material that is not

alkali tolerant, or using

a decorative paint in

place of a higher-per-

formance concrete

coating. While a num-

ber of differences exist

between paint and

coatings, it is generally

acknowledged that film

build is one of the

major distinctions.

Thin-mil materials

(paints) typically range

in dry-mil thickness

from 3 to 5 mils. High-

build materials (coat-

ings) range in dry-film

thickness from 10 to 20

mils. The difference in

film build is primarily

related to the polymer

types employed in

thick-film coatings,

which allow higher solids content with-

out cracking of the cured coating.

The benefits that properly applied

high-build coatings can deliver are

numerous:

• waterproof protection to concrete

structures;

• protection from carbonation of con-

J o u r n a l o f A r c h i t e c t u r a l C o a t i n g s / J u n e / J u l y 2 0 0 8 1 5

Primers should be applied to joints as

recommended by the sealant manufac-

turer. Priming maximizes adhesion to

help keep the building watertight, and

ensures adhesion to special substrates

such as coated metal panels. Primer

application might be viewed as inex-

pensive insurance when weighed

against the cost of a call-back.

Sealant installationThe following steps should be followed

when applying sealants.

• The appropriate size backer rod (25%

larger than joint) is installed to the pre-

scribed uniform depth.

• A joint dimension twice as wide as

deep, to a maximum ½-inch depth, is

recommended.

• The sealant is installed in a continu-

ous bead, then tooled into the joint.

Tooling ensures a strong bond and elim-

inates trapped air within the sealant.

The SWR Institute recommends dry

tooling, as tooling agents such as sol-

vents or soapy water can interfere with

the proper curing of a sealant or cause

discoloration.

Sealant inspectionBuilding construction is an imperfect

science. As hard was we try, mistakes

can be made, buildings can settle, and

acts of God can prevail against the

finest engineering. After all that can be

done has been done, it is important toinspect the façade, and particularly the

sealants, on a regular basis.

Minor issues related to sealants are

easily and economically solved if they

are addressed early. If allowed to go

unchecked, however, they can allow

penetration of significant amounts of

water into wall systems, which can lead

to much more costly repairs in the

future. The old adage of “an ounce of

prevention is worth a pound of cure” is

no more true than in the case of façade

inspection.

Elastomeric sealants and high-build coatings play an imp ortant rolein p rotecting buildings from the elements.

For more info, return Reader Inquiry Card

crete and ingress of chloride ions;

• the ability of elastomeric types of

these coatings to bridge moving cracks

of up to 1/16th inch wide;

• encapsulation of aggregate for aes-

thetics and masking of surface imper-

fections;

• toleration of the naturally higher pH

of concrete substrates;

• aesthetic appeal and color range

equal to or greater than paints; and

• long-term service life.

One of the most important benefits a

high-build coating provides to a con-

crete structure is protection from car-

bonation of the concrete and ingress of

soluble chloride ions. Dilute carbon

dioxide carried in rain, in addition to

atmospheric moisture, lowers the nat-

ural alkalinity of concrete. This natural

alkalinity is actually beneficial, protect-

ing reinforcing steel from corrosion. As

long as the pH of concrete remains

above 9, corrosion of the reinforcing

steel will not occur. Corrosion can occur

prematurely when steel reinforcing is

placed too close to the surface of the

concrete. As carbonation passes through

the concrete, the steel becomes suscep-

tible to corrosion at an earlier stage.5

Studies have shown that the applica-

tion of high-build coatings can combat

the carbonation of concrete.6 This abili-

ty to protect concrete from carbonation

is dependent on the coating’s intrinsic

capacity to diffuse CO2, along with the

dry film thickness. Together, these two

characteristics present a barrier that acts

as simulated concrete cover over the

reinforcing steel.

Concrete is a unique substrate with

unique requirements. Efforts to reduce

costs often go unrewarded when struc-

tures need to be recoated because an

inexpensive paint was used in place of a

protective coating, and the paint subse-

quently fails. Additionally, protecting

concrete from corrosion, carbonation,

and chloride-ion ingress goes beyond

aesthetics to the heart of building life-

cycle, and ultimately public safety.

Surface preparationAs is the case with sealants, proper

preparation is 90% of the battle in

ensuring the successful performance of

exterior wall coatings. As most high-

build coatings bond by means of

mechanical adhesion, surface prepara-

tion is critical.

Frequently encountered surface-

preparation issues involving concrete

buildings can be divided into two cate-

gories: contaminants and surface

imperfections. Common contaminants

include curing compounds, efflores-

cence, form-release agents, and con-

crete laitance. Surface contaminants

may act as bond breakers and inhibit

the proper bonding of coatings.7

Curing compounds are film-forming

acrylic membranes, wax-based emul-

sions, or dissipating hydrocarbons that

are used to aid in the curing of concrete

to facilitate the development of needed

properties. These compounds should be

removed before high-build coatings are

applied. Removal methods vary,

depending on the type of curing com-

pound.

Efflorescence is a soluble salt pro-

duced as a byproduct of cement hydra-

tion in concrete. Generally, laitance is

a crystalline substance that will inhibit

the bond of wall coatings. It can often

be removed by simple power washing,

although stubborn stains may require

chemical cleaners.

Form-release agents are used to aid in

the removal of concrete forms follow-

ing pouring of concrete. These agents

are often petroleum-based materials,

and leave a light, oily film on the con-

crete surface. This film must be

removed before applying a wall coat-

ing.

Concrete laitance is a thin layer of

weak concrete paste on the surface of

the concrete, and is composed of

Portland cement and “fines” carried to

the surface by bleed water. This layer

typically is characterized by a high

water-to-cement ratio, lacks cohesive

strength, and is very friable. Laitance

can be present regardless of whether

the concrete was cast in a form, steel-

troweled, or broom-finished. A com-

mon misconception is that a broom

finish always provides a surface that is

sound enough to receive a coating.

Laitance should be removed through

abrasive blasting or water blasting.

Some common surface imperfections

include bug holes, tie holes, honey-

combs, mortar fins, and cement

slurry.7

Bug holes are small holes that devel-

op on the concrete surface due to a

lack of consolidation of the concrete.

High-build protective coatings are

designed to be applied in a continuous

film layer, but these holes create breaks

in the coating. They should be proper-

ly prepared and patched in accordance

with ACI 301.

Tie holes are holes where anchors

18 J o u r n a l o f A r c h i t e c t u r a l C o a t i n g s / J u n e / J u l y 2 0 0 8

once held the concrete forms together.

These need to be repaired, and should

be prepared and patched in accor-

dance with ACI 301.

Honeycombs result from improper

vibration and consolidation of the

concrete, and can also form below

obstructions in concrete forms. They

often are irregular in shape and may

be obscured by a thin cover of mortar

over voids. These voids need to be

opened up and repaired per ACI 301.

Left untreated, they can crack beneath

the coating, causing delamination.

Mortar fins occur when cement paste

finds its way into gaps between con-

crete forms. Fins or ridges cause high

spots in an applied coating, and can

result in the application of a too-thin

coating film over these ridges. Fins

should be ground flush with the sur-

rounding concrete, per ACI 303.

Application considerationsThe most common application issue

related to high-build coatings is film

uniformity. When properly applied, a

high-build coating provides a continu-

ous layer of protection over the exteri-

or of the building. As is the case with

fluid-applied waterproofing for below-

grade applications, high-build protec-

tive coatings for above-grade settings

should be applied at a uniform thick-

ness, with assurance that pinholes and

other coating defects do not occur.

High-build coatings work together

with the other elements of the wall

system to provide a barrier of protec-

tion for the building. The presence of

pinholes, holidays, and skips in the

applied coating can be likened to holes

in the bottom of a boat. These voids

not only allow moisture to penetrate

the wall system, but also provide an

avenue to carbonation and chloride-

ion ingress. Additionally, pinholes and

holidays allow moisture to migrate

behind the wall coating, and often

lead to the formation of efflorescence

and, eventually, delamination of the

coating, exposing more of the sub-

strate.

Job-site issuesAs long as humans continue to design

and build buildings, human error is

inevitable. In many ways, concrete is

an ideal construction material—it is

versatile, economical, and durable. It

can, however, present some challenges

that affect the building envelope’s

capacity to resist moisture. These chal-

lenges can affect the performance of

the wall system as well as the wall

coating and sealant.

Moisture resistance in the building

exterior can be compromised in a

number of ways and at various parts of

the exterior. These are reviewed in the

following discussion.

Placement of reinforcement.Steel reinforcement placed too close to

the finished surface can result in pre-

mature corrosion of the steel reinforce-

ment, leading to spalling of the con-

crete. ACI 301 requires that steel be

covered with at least two inches of

concrete. If an insufficient concrete

cover is recognized before the building

is put into service, a high-performance

coating may be applied to the concrete

to protect it from early carbonation

and steel corrosion.

Cracking. The concrete industryhas made great strides in the formula-

tion and installation of concrete to

minimize cracking; however, cracking

still occurs in both precast and cast-in-

place concrete. Cracks provide an

avenue for moisture, oxygen, and chlo-

rides to reach the reinforcing steel.

This can accelerate corrosion of steel

reinforcement, induce concrete

spalling, and lead to premature deteri-

oration of wall components, including

anchors, drywall, and interior finishes.

Treatment of cracks will vary depend-

ing on the type of structure, crack loca-

tion, and aesthetic requirements.

Window openings. Windows rep-resent a common entry point for mois-

ture. Window sills are typically sloped

to allow moisture to be deflected away

from the window. A condition often

observed on concrete buildings (cast in

place, precast, and tilt wall) is the pres-

ence of flat window sills. This allows

water to collect and potentially find its

way to the building interior. Horizontal

surfaces require different coating mate-

rials in order to perform properly. This

adds cost and complications to the pro-

ject.

Sealant width-to-depth ratio.While this concept is simple, it remains

common to find the wrong-sized

backer rod doubled up to fill a larger

joint. This configuration leads to

restraint within the sealant, almost

always resulting in cohesive failure. It

is also common to find sealant

installed too deep. This can lead to

cohesive or even adhesive failure, as

the deep-set sealant bead places so

much stress on the bondline that the

bonding forces are overwhelmed.

Parapet details. On precast orcast-in-place buildings, parapet caps are

often eliminated. The expansion joint

is carried up the wall and over the top.

This is an area that often is prone to

leaks. Best practice would dictate

installing a parapet cap at the top of

walls. Parapet caps, however, also can

serve as a common point of entry for

wind-driven rain. Caulking on the

underside of the hemmed edge of the

parapet cap, though a good practice, is

often overlooked or omitted. Lastly, the

back of the parapet wall should be

coated. A good practice is to bring the

roofing material up the back of the

parapet wall and terminate it under the

parapet cap. More often than not, it’s

what you don’t see that causes most of

the problems.

The role of mock-upsIt is important to verify compatibility of

materials before work commences.

While previous experience is a good

indicator, it is best to install a mock-up

on the job site with the actual materials

that will be used on the project. Paint

formulations for coated window frames

can change over time. Where a sealant

once adhered well, it may now require

additional surface preparation or a dif-

ferent primer.

A field mock-up for sealant adhesion

involves preparing the joint, installing

the backer rod and sealant, and then

allowing the sealant to cure. ASTM

C1521 provides both destructive and

non-destructive procedures for evaluat-

ing the adhesion of sealants in the field.

While the destructive test has the

advantage of also showing the full pro-

file of the sealant and is commonly

used to evaluate mockups, the non-

destructive test may be more practical

for ongoing inspection during the pro-

ject.8

Coatings mock-ups provide a repre-

sentative example to the owner and

specifier of the final aesthetic of the

coating. It also helps the contractor

determine the application method

needed to achieve a pinhole-free film.

Wall-coating mock-ups protect all par-

ties involved. Memories quickly fade,

but mock-ups can serve as the ultimate

arbiter in any questions or conflicts

involving failures. Mock-ups should be

applied on an inconspicuous area of the

building and remain there until coating

application has been completed.

In addition to mock-ups, job-site vis-

its from qualified manufacturers repre-

sentatives can help prevent problems

before they occur. Manufacturers work-

ing with the contractor to address

preparation and application questions

can help ensure that what is specified is

what is used on the project.

Melding the partsto create the whole

This article has sought to identify and

discuss some of the more common

issues related to moisture protection of

concrete buildings. Specifically, the dis-

cussion has focused on issues related to

selecting and installing elastomeric

sealants and selecting and applying pro-

tective wall coatings.

Together, sealants and wall coatings

Formore

info,returnReaderInquiry

Card

J o u r n a l o f A r c h i t e c t u r a l C o a t i n g s / J u n e / J u l y 2 0 0 8 1 9

JAC

20 J o u r n a l o f A r c h i t e c t u r a l C o a t i n g s / J u n e / J u l y 2 0 0 8

combine to form a barrier of protection

around concrete buildings. They protect

buildings from the negative affects of

moisture ingress, including water dam-

age to building elements and its con-

tents; mold; poor indoor air quality;

and damaged finishes. In addition to

providing waterproofing protection for

building exteriors, high-build coatings

protect concrete buildings from the

detrimental effects of carbonation and

chloride-ion ingress.

Building envelopes are composed of a

variety of materials working together as

a system to protect occupants from the

forces of nature: wind, rain, heat, and

cold. These components are designed by

professionals and installed by skilled

trades.

While many common problems that

can compromise the performance of a

building envelope have been observed

in the field, these problems and failures

are not inevitable. Proper material selec-

tion, surface preparation, and material

installation, along with the use of job-

site mock-ups and post-installation

inspections, can ensure that the build-

ing meets the primary objective that

has remained constant over the cen-

turies: keeping water out of the struc-

ture.

References1. www.swronline.org

2. www.swronline.org

3. ACI 504 R90 Guide to Sealing Joints

in Concrete Structures.

4. ACI 515.1R-29 A Guide to the Use of

Waterproofing, Dampproofing,

Protective, and Decorative Barrier

Systems for Concrete.

5. ACI 224 Causes, Evaluation and

Repair of Cracks in Concrete

Structures.

6. Hurley, Shaun A., “The Long-Term

Durability and Performance

Assessment of Coated Concrete,”

Journal of Protective Coatings and

Linings, September 2000.

7. Holl, Charles H, O’Connor, Scott A,

“Cleaning and Preparing Concrete

before Repair,” Concrete

International, March 1997.

8. ASTM C1521-02a, “Standard Practice

for Evaluating Adhesion of Installed

Weatherproofing Sealant Joints”,

ASTM International, Conshohocken

PA.

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