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How to apply high voltage insulator coating?

Midsun IKM's CEO, Imad Kanouni, made a video to go over the basic steps of every application process of high voltage insulator coating. He resumes that the RTV Silicone High Voltage Insulator Coating can be applied in 4 steps: surface preparation, mixing, application and drying.

We are going to go deeper and explain how the Flashover Insulators RTV Coating must be applied.

What are the steps to apply high voltage insulator coating?


Depending on the type of surface contamination, insulators should be cleaned using rag soaked with solvent (e.g., isopropyl, alcohol, ethanol, acetone, among others). Please note that rags must be replaced often while cleaning.

Cleaning Insulators before the coating application
Surface preparation before applying HVIC

For insulators covered with silicone compounds or other types of greases, bulk of the silicone compounds or greases shall be removed with a dry abrasive cleaner (e.g., blowing with crushed corncob or walnut shells mixed with limestone) or by hand wiping using solvent-dipped rags. Once the bulk of the grease has been removed, the surface should be wiped clean using an oil-free solvent.

Solvent used for the final wipe depends on the environmental factors such as temperature, humidity and dew point. Though isopropyl alcohol is highly suggested for final wipe, however it will not be as effective as it is at lower temperature. Thus, at lower temperature, acetone may be required for the final wipe. Soaps are not advisable for cleaning due to its characteristic to act as release agents and make good adhesion impossible.

After the insulator surface has been cleaned and dried thoroughly, the coating operation must commence without delay in order to avoid dust and/or atmospheric pollutants settling on the cleaned surface. The following conditions must be observed before Midsun HVIC is applied:

1. The surface must be dry and free of dust and/or frost.

2. The ambient conditions must be clear of fog, mist or rain.

3. The temperature must be greater than 9°F (5°C) above the dew point.

4. Windy and dusty conditions must be avoided.


Amount required for Midsun HVIC coating depends on the diameter of the core, diameter of sheds and creepage distance as well on the types of insulators. To prepare Midsun’s HVIC coating, open the container and mix with a proper beater at a medium speed for 10 minutes. High speed air-powered drill with mixing attachment is advisable for thoroughly mixing Midsun HVIC prior to use. Provide plastic sheets to contain spills and/or splashes when mixing coatings prior to application.

Mixing Midsun's HVIC - Mixing High Voltage Insulator Coating
Mixing HVIC

Note: Do not mix Midsun HVIC with solvent prior to application. Adding solvent to the coating will lead to runs, loss of dry film thickness and reduced hide, particularly when spraying a light- colored coating over a dark-colored substrate.


A variety of application methods are possible depending on the needs, it can be by spraying, brushing, or dipping.

Midsun's HVIC application spraying technique
Application of HVIC

Spraying is the most common method for large quantities of coating. This is best carried out using a fabricated support frame to carry the insulators. There are different application techniques for spraying like electric and pneumatic airless systems.

Apply the first coating in a thin layer, start by applying the coating on the core and inner flap and then the upper flap. This will ensure a build-up without any runs or streaks. Allow the first coat to dry for 10-15 minutes and when the first coat becomes tacky, apply subsequent coats. Ensure that all parts of the insulator skirts be completely coated all the way into the concentric “valleys” between the skirt ridges.

For maximum protection and life expectancy, Midsun Group recommends using two to three coats, depending upon the method and equipment used.


Let each layer dry for at least 20 minutes before applying the next one. The coated insulators should be left for at least 2 hours in a dust free area, before being carefully turned over to allow the top sides to be coated. Leave the insulators a further 24 hours to ensure a complete cure.

Dry coated insulator with Midsun HVIC
Drying process of HVIC

After a complete cure, wrap each insulator individually with “bubble wrap” plastic sheets, so that the coated surfaces are completely covered. Attach the bubble wrap sheets to the metal hardware areas of the insulators using adhesive tape. This bubble wrap is to remain on all insulators until the insulator strings have been assembled and installed into position at the job site. Only then can the bubble wrap be removed.


Midsun IKM is the international business unit of Midsun Group, a company that has developed HVIC RTV Silicone High Voltage Insulator Coating since the early nineties. Midsun has gathered substantial experience throughout the years and knows the best ways to use and implement the product to avoid weather-induced flashovers on any type of insulators. If you want to know more on how to apply RTV coating, you can contact us.

Midsun IKM also offers RTV Silicone Coating Service. The so-called turnkey projects, training and supervision and consulting can be found here.


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