Post on 18-Jul-2015
Overcoating Water TanksOvercoating Water Tanks
Jim Skilton & Jeff WhiteSouthern Corrosion & Induron Protective Coatings
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
• 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
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