Application Tips


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 :


a. 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.


b. Sandblasting, or 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.


c. 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.


d. Sanding, or 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.


e. 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.

 

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. The tasks involved can be basically broken down into the following categories :

* Selecting the right material alongwith its right combination for lining.
* Studying and comparing its performance theoretically with other modes of lining.
* Survey of the surface on which the lining is to be done.
* Estimation of the thickness of the lining that would be required.
* Applying the epoxy lining with utmost care and precision.
* Carrying out the post-lining inspections for pin holes & thickness, etc.
* Allowing the lining to reach complete curing before it can be put to use.


Each of the above steps are described in detail in the following sections.


Selection of the right material for lining.

The choice of the system depends on the following factors:

(i) The chemicals to be handled, whether for storage in case of tanks lining or transmission in case of piping lining, etc.
(ii) The degree of corrosiveness of the chemical and the various conditions it is subject to ..viz.. maximum pressure, maximum temperature, etc.
(iii) The degree of abrasion in the supply mode.
(iv) Various stresses the equipment would be subjected to when put into operation.
(v) Curing time required.

Apart from these 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 is very important before undertaking the coating jobs. Present condition of the corroded site should be taken account of and also the reasons for corrosion should also be noted down,viz.

(i) Extent of corrosion and the causes for it.
(ii) Presence of loose scales on the vessel or piping surface.
(iii) Chemical residues on the surface.
(iv) Rust, oil, grease, etc. on the surface.
(v) Extent of moisture and humidity at the area of application.
(vi) Accessibility to the area of application.
(vii) 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 of the lining required.

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 .

(i) Should provide the mechanical strength required.
(ii) 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.



After carrying out the various pre-lining jobs applying the epoxy lining.


Application of 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.



Carrying out the post Lining inspections.

Checking for gaps, pin holes and the proper thickness.

After the lining job has been completed, the following inspections may be carried out.

(i) 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.

(ii) Thickness test : Thickness is tested by conventional methods (if possible) such as by vernier calipers, Screw gauge, etc.

(iii) 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.


Allowing the lining to complete curing before the vessel or equipment can be put to use.

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 stream of hot air on the surface.