Overcoating Water TanksOvercoating Water Tanks

Jim Skilton & Jeff WhiteSouthern Corrosion & Induron Protective Coatings

OverCoating Paint Systems on Water Tanks

We never know the worth of water till the well is dry.

-English Proverb

38% OF EXISTING INDUSTRIAL STEEL HAS BEEN COATED WITH LEAD-BASED PAINT INCLUDING

OVER 51,000 WATER TANKS.

Check Adhesion and FilmIntegrity

• What is the total film thickness?

• How many coats of paint?

• How good is the adhesion to the substrate and between coats?

• Are there film defects such as cracking or blistering?

Degree of Rusting

• ASTM D 610 Evaluating Degree of Rusting on Painted Steel Surfaces

• Less Than 10% Rusting

• Clean, Dry & Free of Contaminants

• Power Washing with Detergent

• Spot Power Tool Cleaning

- SSPC-SP3

- SSPC-SP11

Surface Preparation for Overcoat Systems

Surface Preparation for Overcoat Systems

• Evaluate the Degree of Rusting

• Evaluate the Adhesion & Film Integrity

Determining the Condition of the Existing Paint System

• The condition of the existing coating system

• The surface preparation prior to overcoating

• The geographic location (exposure conditions)

• The type of overcoat system selected

• Selecting a knowledgable, experienced contractor

• Owner expectations

Factors that Determine Overcoat Success

Selecting a Successful Overcoat System

DETERMINING THE DELAMINATION RISK FACTOR

Delamination Risk Factor

The degree of risk associated with the existing coating system delaminating between coats, or from the substrate after application of an overcoat system taking into account freeze/thaw cycling and total film thickness of the existing system.

DELAMINATION RISK FACTOR

0 Poor 5 High 5+ 5++

1 - 4.5 - 5 5+

2 - 4 - 4.5 5

3 - 3 - 3.5 4

4 - 2 - 2.5 3

5 Excellent 1 Low 1.5 2

AdhesionResults

Delamination Risk Factor

(D.R.F.)

Delamination Risk Factor w/

Freeze & Thaw

D.R.F. w/ Freeze & Thaw Cycling & High D.F.T.

COHESIVE STRESS FACTORS

Elastomeric Acrylic Emulsions 1 Low

Acrylic Emulsions 2 -

Medium to Long Oil Alkyds 3 -

Epoxy Mastics 4 -

Conventional 2-component 5 Highepoxies, aliphatic urethanes andmoisture-cured urethanes

Generic Type Cohesive Stress Factor

SELECTING CANDIDATEOVERCOAT SYSTEMS

Delamination Risk Factor

5 None Recommended

4.5 None Recommended

4 1 or 2

3 1, 2, 3 or 4

2 1, 2, 3, 4 or 5

1 1, 2, 3, 4 or 5

Candiate Overcoat SystemsBased on Cohesive Stress Factors

Adhesion / Film Integrity

+

Geographic Location

+

Existing Film Thickness

DELAMINATION RISK FACTOR

Delamination Risk Factor

+

Cohesive Stress Factor

CANDIDATE OVERCOAT SYSTEM

Candidate Overcoat System

+

Test Patch Evaluation

SUCCESSFUL OVERCOAT SYSTEM

Excellence is not an act, but a habit

-Aristotle

Question? Comments? Discussions?