Application Tips
Procedures, Standards & Best Practices for Epoxy Lining and Surface Preparation
Concrete Sub-Surface Preparation
The objective of subsurface preparation is to provide maximum chemical and mechanical bond potential between the cured concrete subsurface and epoxy layer.
The concrete must be made clean, dry, free of any oil, grease or other bond breaking contamination.
New concrete subsurfaces must be cured for at least 28 days, or longer, if required to reach full design strength and low enough moisture content to permit overlayment.
The prepared concrete subsurface must be treated to provide an etched, porous, a “toothy” profile, yet be structurally and integrally sound.
Procedures and Standards for Concrete and Metal Surface Preparation
Shotblasting
Using steel shot and self-contained abrasive blasting equipment. Blasting should be performed so as to leave clean, “white” concrete with a uniform stipple finish.
Sandblasting
Use of other pneumatically impelled abrasive media, is another acceptable method of preparing both vertical and horizontal surfaces. Care must be taken to provide a uniformly textured surface.
Scarifying
Using motorized scarification equipment, generally incorporating rotating banks of hardened, star-shaped steel teeth, is particularly useful when high builds of soft materials must be removed. These may include coatings which do not respond to shotblasting, or unsound thin cementitious overlayments.
Sanding
Surface abrasion with heavy grit media is often used to reach corners and edges in conjunction with shotblasting. It is also useful when recoating sound epoxy surfaces to improve intercoat bonding when removal down to subsurface is not required or desired.
Chemical & Light Mechanical Treatment
For areas which are weak or which are not accessible for above operation, viz. oil contaminated area or in platforms standing unmovable structures; we recommend the chemical and light mechanical treatment procedure.
Surface Preparation Standards
National Association of Corrosion Engineers (NACE)
Removal of all mill scale, rust, scale, paint or foreign matter by the use of abrasives propelled through nozzles or by centrifugal wheels. A White Metal Blast Cleaned Surface Finish is defined as a surface with a gray-white, uniform metallic color, slightly roughened to form a suitable anchor pattern for coatings. The surface, when viewed without magnification, shall be free of all oil, grease, dirt, visible mill scale, rust, corrosion products, oxides, paint, or any other foreign matter.
Removal of nearly all mill scale, rust, rust scale, paint, or foreign matter by the use of abrasives propelled through nozzles or use of centrifugal wheels. A Near-White Blast Cleaned Surface Finish is defined as one from which all oil, grease, dirt, mill scale, rust, corrosion products, oxides, paint or other foreign matter have been completely removed from the surface except for very light shadows, slight streaks or the slight discolorations caused by rust stain, mill scale oxides, or light, tight residues of paint or coating that may remain. At least 95% of each square inch of surface area shall be free of all visible residues, and the remainder shall be limited to the light discoloration mentioned above.
Removal of mill scale, rust, scale, paint or foreign matter by the use of abrasives propelled through nozzles or by centrifugal wheels. A Commercial Blast Cleaned Surface Finish is defined as one from which all oil, grease, dirt, rust, scale and foreign matter have been completely removed from the surface and all rust, mill scale and old paint have been completely removed except for slight shadows, streaks, or discolorations caused by the rust stain, mill scale oxides or slight, tight residues of paint or coating that may remain; if the surface is pitted, slight residues of rust or paint may be found in the bottom of pits; at least two-thirds of each square inch of surface area shall be free of all visible residues and remainder shall be limited to the light discoloration, slight staining or tight residues mentioned above.
Steel Structures Painting Council (SSPC)
Removal of all detrimental foreign matter such as oil, grease, dirt, soil, salts, drawing and cutting compounds, and other contaminants from steel surfaces by the use of solvents, emulsions, cleaning compounds, steam or other similar materials and methods which involve solvent or cleaning action.
Removal of all rust scale, mill scale, loose rust and loose paint to the degree specified by hand wire brushing, hand sanding, hand scraping, hand chipping or other hand impact tools or by a combination of these methods. The substrate should have a faint metallic sheen and also be free of oil, grease, dust, soil, salts and other contaminants.
Removal of all rust scale, mill scale, loose paint, and loose rust to the degree specified by power wire brushes, power impact tools, power grinders, power sanders or by a combination of these methods. The substrate should have a pronounced metallic sheen and also be free of oil, grease, dirt, soil, salts and other contaminants. Surface should not be buffed or polished smooth.
Removal of all loose scale, rust and other detrimental foreign matter by passing high temperature, high velocity oxy-acetylene flames over the entire surface, followed by wire brushing. Surface should also be free of oil, grease, dirt, soil, salts and other contaminants.
Removal of all mill scale, rust, scale, paint or foreign matter by the use of abrasives propelled through nozzles or by centrifugal wheels. A White Metal Blast Cleaned Surface Finish is defined as a surface with a gray-white, uniform metallic color, slightly roughened to form a suitable anchor pattern for coatings. The surface, when viewed without magnification, shall be free of all oil, grease, dirt, visible mill scale, rust, corrosion products, oxides, paint, or any other foreign matter.
Removal of mill scale, rust, scale, paint or foreign matter by the use of abrasives propelled through nozzles or by centrifugal wheels. A Commercial Blast Cleaned Surface Finish is defined as one from which all oil, grease, dirt, rust, scale and foreign matter have been completely removed from the surface and all rust, mill scale and old paint have been completely removed except for slight shadows, streaks, or discolorations caused by the rust stain, mill scale oxides or slight, tight residues of paint or coating that may remain; if the surface is pitted, slight residues of rust or paint may be found in the bottom of pits; at least two-thirds of each square inch of surface area shall be free of all visible residues and remainder shall be limited to the light discoloration, slight staining or tight residues mentioned above.
Removal of loose mill scale, loose rust, and loose paint, to the degree hereafter specified, by impact of abrasives propelled through nozzles or by centrifugal wheels. It is not intended that the surface shall be free of all mill scale, rust, and paint. The remaining mill scale, rust, and paint should be tight and the surface should be sufficiently abraded to provide good adhesion and bonding of paint. A Brush-Off Blast Cleaned Surface Finish is defined as one from which all oil, grease, dirt, rust scale, loose mill scale, loose rust and loose paint or coatings are removed completely but tight mill scale and tightly adhered rust, paint and coatings are permitted to remain provided that all mill scale and rust have been exposed to the abrasive blast pattern sufficiently to expose numerous flecks of the underlying metal fairly uniformly distributed over the entire surface.
Removal of all mill scale, rust and rust scale by chemical reaction, or by electrolysis, or by both. It is intended that the pickled surface shall be completely free of all scale, rust, and foreign matter. Furthermore, the surface shall be free of unreacted or harmful acid or alkali, or smut.
Weathering to remove all or part of the mill scale followed by one of the blast cleaning standards.
Removal of nearly all mill scale, rust, rust scale, paint, or foreign matter by the use of abrasives propelled through nozzles or use of centrifugal wheels. A Near-White Blast Cleaned Surface Finish is defined as one from which all oil, grease, dirt, mill scale, rust, corrosion products, oxides, paint or other foreign matter have been completely removed from the surface except for very light shadows, slight streaks or the slight discolorations caused by rust stain, mill scale oxides, or light, tight residues of paint or coating that may remain. At least 95% of each square inch of surface area shall be free of all visible residues, and the remainder shall be limited to the light discoloration mentioned above.
Swedish Standards (St, Sa)
Removal of all rust scale, mill scale, loose rust and loose paint to the degree specified by hand wire brushing, hand sanding, hand scraping, hand chipping or other hand impact tools or by a combination of these methods. The substrate should have a faint metallic sheen and also be free of oil, grease, dust, soil, salts and other contaminants.
Removal of all rust scale, mill scale, loose paint, and loose rust to the degree specified by power wire brushes, power impact tools, power grinders, power sanders or by a combination of these methods. The substrate should have a pronounced metallic sheen and also be free of oil, grease, dirt, soil, salts and other contaminants. Surface should not be buffed or polished smooth.
Removal of loose mill scale, loose rust, and loose paint by impact of abrasives propelled through nozzles or by centrifugal wheels. It is not intended that the surface shall be free of all mill scale, rust, and paint. The remaining mill scale, rust, and paint should be tight and the surface should be sufficiently abraded to provide good adhesion and bonding of paint.
Removal of mill scale, rust, scale, paint or foreign matter by the use of abrasives propelled through nozzles or by centrifugal wheels. A Commercial Blast Cleaned Surface Finish is defined as one from which all oil, grease, dirt, rust, scale and foreign matter have been completely removed from the surface and all rust, mill scale and old paint have been completely removed except for slight shadows, streaks, or discolorations caused by the rust stain, mill scale oxides or slight, tight residues of paint or coating that may remain; if the surface is pitted, slight residues of rust or paint may be found in the bottom of pits; at least two-thirds of each square inch of surface area shall be free of all visible residues.
Removal of nearly all mill scale, rust, rust scale, paint, or foreign matter by the use of abrasives propelled through nozzles or use of centrifugal wheels. A Near-White Blast Cleaned Surface Finish is defined as one from which all oil, grease, dirt, mill scale, rust, corrosion products, oxides, paint or other foreign matter have been completely removed from the surface except for very light shadows, slight streaks or the slight discolorations caused by rust stain, mill scale oxides, or light, tight residues of paint or coating that may remain. At least 95% of each square inch of surface area shall be free of all visible residues.
Removal of all mill scale, rust, scale, paint or foreign matter by the use of abrasives propelled through nozzles or by centrifugal wheels. A White Metal Blast Cleaned Surface Finish is defined as a surface with a gray-white, uniform metallic color, slightly roughened to form a suitable anchor pattern for coatings. The surface, when viewed without magnification, shall be free of all oil, grease, dirt, visible mill scale, rust, corrosion products, oxides, paint, or any other foreign matter.
Procedural Steps for Carrying out an Epoxy Lining
The right procedure of coating plays an equally important role as the epoxy used for the lining.
Select the Right Material
Selecting the right material along with its right combination for lining.
Study Performance
Studying and comparing its performance theoretically with other modes of lining.
Survey the Surface
Survey of the surface on which the lining is to be done.
Estimate Thickness
Estimation of the thickness of the lining that would be required.
Apply with Precision
Applying the epoxy lining with utmost care and precision.
Post-Lining Inspection
Carrying out the post-lining inspections for pin holes & thickness, etc.
Complete Curing
Allowing the lining to reach complete curing before it can be put to use.
Selection of the Right Material for Lining
The choice of the system depends on the following factors:
- The chemicals to be handled, whether for storage in case of tanks lining or transmission in case of piping lining, etc.
- The degree of corrosiveness of the chemical and the various conditions it is subject to — viz. maximum pressure, maximum temperature, etc.
- The degree of abrasion in the supply mode.
- Various stresses the equipment would be subjected to when put into operation.
- Curing time required.
Care has to be taken that the mixing is done in the proper ratio (approx.) and that the mixing is vigorous and complete. Improper mixing may tender the lining ineffective or susceptible to failure.
On Site Survey
Present condition of the corroded site should be taken account of and also the reasons for corrosion should also be noted down:
- Extent of corrosion and the causes for it.
- Presence of loose scales on the vessel or piping surface.
- Chemical residues on the surface.
- Rust, oil, grease, etc. on the surface.
- Extent of moisture and humidity at the area of application.
- Accessibility to the area of application.
- Strength of the plate or piping on which lining is to be done.
On the basis of the survey the mode of action is decided and the equipments required for cleaning are brought to the site.
Estimation of Thickness
After the survey has been conducted the thickness required is gauged on the basis of trials, tests and experience. The coating thickness provided should fulfill the following requirements:
- Should provide the mechanical strength required.
- Should be thick enough to resist pitting and pore formation.
Care should be taken that the coating is not too thick as it tends to increase the weight of the vessel or equipment and at the same time shift its weight distribution.
Application of Lining
After carrying out the various pre-lining jobs, applying the epoxy lining:
- First it is made sure that all the pre-coating instructions have been followed.
- Then the required Resin and Curing agent are mixed in the required ratio.
- Care is taken to take small quantities at a time, so that the material doesn't harden up before application.
- Separate removal sticks / spatulas should be taken for the removal of both resin and curing agent. Also care should be taken that the sticks don't mix up as it would render the entire material useless.
- Apply the material from bottom to top for vertical surfaces as epoxy will tend to flow down.
- Don't leave the edges of the coating blunt, make them as smooth & even as possible for a longer life.
- Do not touch the coating till it has completely dried up.
- Apply second layer of coating for greater thickness (if required) only after the first coating has dried up.
- Give the coating sufficient time before the equipment is put into operation.
Post Lining Inspections
After the lining job has been completed, the following inspections may be carried out:
Spark Test
Spark test is carried out to ensure that no exposed part has been skipped for lining. Such an exposed part can lead to the failure of the entire job. Care should be taken that the voltage of the spark meter is set so as to indicate failure only for a certain coating thickness.
Thickness Test
Thickness is tested by conventional methods (if possible) such as by vernier calipers, screw gauge, etc.
Visual Inspection
Finally a visual inspection is done to ensure that the resin & curing agent have been properly blended in all surfaces and that no part is sticky or uncured.
Curing
Always ensure that the coating has been completely dried up before putting the applicated surface into operation.
In case you wish to cure the coating quickly, blow a stream of hot air on the surface.