For most workshop and site repairs of LV motors, generators and small transformers, use an air-drying, solvent-based insulating varnish of thermal class F (155 °C) or better, applied by brush on accessible windings or by dipping the complete stator, in two thin coats, touch-dry in about 30 to 60 minutes and fully cured after 24 hours at room temperature (faster in a warm oven). Choose a baking (oven-cured) varnish or an impregnating resin for new windings and class H (180 °C) machines, and a water-based varnish where solvent fumes are not acceptable. A 1000 ml tin covers roughly 4 to 6 m² per coat. Clean and dry the winding first, test the insulation resistance before and after, and energise only after the full cure.
Step by step
- Confirm the winding’s thermal class and conditionRead the motor or transformer nameplate for the insulation class (B 130 °C, F 155 °C, H 180 °C) and the ambient; the varnish class must be equal or higher. Check the winding is mechanically sound and the insulation resistance is acceptable before varnishing: varnish protects a good winding, it does not repair a failed one.
- Choose the varnish typeAir-drying solvent-based varnish for maintenance and repair without an oven; baking varnish or impregnating resin for new or rewound coils cured in an oven (better penetration and bond); water-based varnish where fumes and flammability must be avoided; red or clear finishing varnish for the visible end windings and a corrosion-resistant top coat.
- Choose the application methodBrush for end windings, connections and accessible coils; dip the whole stator or coil (then drain and rotate) for complete penetration of the slot area; spray for large surfaces and quick top coats. Thin the varnish only with the thinner the maker names, to the viscosity for the method.
- Prepare the windingClean with an approved electrical cleaner or dry compressed air, remove oil, carbon dust and loose varnish, and dry the winding thoroughly (a warm oven at 80 to 100 °C for several hours removes trapped moisture). Mask bearings, shafts, terminals and slip rings.
- Apply in thin coatsApply a thin, even first coat and let the solvent flash off; apply a second coat where the first soaked in. Thick coats trap solvent, stay soft and crack. For dipping, immerse until bubbling stops, lift, drain and rotate slowly so the film is even.
- Dry and cureAir-drying varnish: touch-dry in 30 to 60 minutes, handle after a few hours, full hardness after 24 hours at 25 °C; warm air shortens it. Baking varnish: follow the maker’s oven schedule (typically 2 to 4 hours at 120 to 150 °C). Energise only after the full cure.
- Test and recordMeasure the insulation resistance (and polarisation index on larger machines) after the cure and compare with the value before; record the varnish type, batch and date on the repair sheet so the next maintenance knows what was applied.
What insulating varnish does
Electrical insulating varnish is a liquid polymer (alkyd, polyester, epoxy-ester or polyurethane in a solvent or water carrier) applied to a finished winding. When it dries or cures it forms a continuous film that fills voids between turns, excludes moisture, dust, oil and chemical vapours, bonds the conductors so they do not move under electromagnetic forces, and raises the surface resistance against tracking and partial discharge. It is the last step of every rewind and a routine step in motor and transformer maintenance.
It is not a substitute for the slot insulation or the wire enamel: a winding that has failed electrically must be rewound, not revarnished.
Varnish types compared
| Type | Cure | Thermal class | Where it fits | Notes |
|---|---|---|---|---|
| Air-drying solvent-based | Room temperature; touch-dry 30 to 60 min, hard in 24 h | F (155 °C), some H | Repair and maintenance on site and in workshops without an oven | Flammable solvent: ventilation, no ignition sources |
| Baking (oven-cured) | Oven, typically 2 to 4 h at 120 to 150 °C | F and H | New windings, rewinds, dip-and-bake lines | Harder film, better bond and penetration |
| Impregnating resin (polyester, epoxy) | Oven or catalysed | F and H | Full impregnation of stators and coils (dip, trickle, VPI) | Solventless, highest fill; production and large repairs |
| Water-based | Room temperature or warm air | F | Enclosed workshops, where flammable fumes are not acceptable | Lower odour; slower drying in humid air |
| Finishing / anti-tracking (red or clear) | Air-drying | F | Top coat on end windings, bus bars, transformer surfaces | Adds surface protection and a visible finish |
Temperature class: B, F or H
The thermal class is the maximum continuous temperature the insulation system is rated for: class B 130 °C, class F 155 °C, class H 180 °C (IEC 60085). Most LV industrial motors sold in Saudi Arabia are class F with class B temperature rise, so a class F varnish is the normal choice; class H machines (high ambient, hazardous-area motors, traction, some transformers) need a class H varnish. Using a lower-class varnish than the winding lowers the whole system to that class.
Brush, dip or spray
- Brush: the method for maintenance: end windings, connections, coils you can reach, small transformers. Two thin coats.
- Dip: immerse the complete stator, rotor or coil after warming it slightly (better flow), drain and rotate; the standard for rewinds where an oven is available. Follow with baking for a baking varnish.
- Spray: fast top coats on large surfaces; use the thinner named by the maker and respect the explosion hazard of the mist.
- Viscosity: dip varnish is thinner than brush varnish; the maker’s data sheet gives the viscosity (or flow-cup seconds) for each method. Never thin with a solvent that is not named.
Drying, curing and coverage
Air-drying varnish is touch-dry in roughly 30 to 60 minutes at 25 °C, can be handled after a few hours and reaches service hardness after about 24 hours; a warm oven (60 to 80 °C) or warm circulating air shortens the time. Baking varnishes cure in the oven according to the maker’s schedule. Coverage of a 1000 ml tin is about 4 to 6 m² per coat by brush and less by dip (the stator absorbs varnish). Energise the machine only after the full cure and a satisfactory insulation-resistance test.
In Saudi workshops the summer ambient speeds up drying but also makes the film skin over before the solvent has left a thick coat: keep coats thin and work in the shade or indoors.
Safety and storage
Solvent-based varnishes are flammable and their vapours are heavier than air: work in a ventilated area, away from ignition sources, with gloves and eye protection, and keep the tin closed when not in use. Store cool, dry and out of the sun; the usual shelf life is about 24 months unopened. The safety data sheet (SDS) states the hazard classification (GHS flammable, health hazard, irritant) and comes with our quotation on request.
Worked example: rewound 15 kW motor in a Jeddah workshop
A 15 kW, 400 V, class F induction motor has been rewound. The workshop has a small oven and the motor returns to a food plant with wash-down areas.
- Class: F winding, so a class F (or H) varnish. The customer wants a moisture-resistant finish, so an air-drying solvent-based insulating varnish with a corrosion-resistant film is chosen; a baking varnish would also suit because an oven is available.
- Method: dip the stator warm, drain and rotate, then brush the end windings after the first coat has flashed off.
- Quantity: one 1000 ml tin covers the stator for two coats with some to spare; order two tins for the workshop stock.
- Cure: 24 hours at room temperature, or a few hours in the oven at the data-sheet temperature; insulation resistance measured before and after and recorded on the repair sheet.
Ordering line: "Allopar insulating varnish, 1000 ml tin, brush/dip, 2 pcs, with technical and safety data sheets."
For larger jobs we also supply AMA insulation varnish: red in 5 litre tins, a red high-temperature grade, a clear finishing grade and the motor and transformer grade.
What to send us for a quotation
The machine type and insulation class, the method you will use (brush, dip or spray), whether you have an oven, the quantity in tins or litres, and any thinner or cleaner you need with it. We quote Allopar insulating varnish in 1000 ml tins, AMA insulation varnish (red 5 litre, red high-temperature, clear, motor and transformer grade) and the other items of our maintenance chemicals group with datasheets, usually within 24 hours, and deliver across Saudi Arabia.
Common questions
What is AMA insulation varnish and which grades do you supply?
AMA is a trade name of electrical insulation varnish for motor and transformer windings. We supply it in four grades: red in 5 litre tins, red high-temperature, clear, and the grade for motors and transformers; part details are on the AMA brand page and each grade is quoted with its datasheet.
Which varnish for a class F motor?
A class F (155 °C) or class H insulating varnish. For maintenance without an oven use an air-drying solvent-based varnish applied by brush or dip; for a full rewind with an oven a baking varnish or impregnating resin gives a harder, deeper bond.
Can I varnish a motor without removing the rotor?
For a light maintenance coat on the accessible end windings, yes, with the rotor masked and the machine isolated and proved dead. For a proper coat of the slot area the stator should be dipped, which needs the rotor out.
How long before I can run the motor?
After the full cure: about 24 hours at room temperature for an air-drying varnish, or the oven schedule for a baking varnish, and only after an insulation-resistance test. Touch-dry after an hour is not cured.
How much varnish do I need?
About 4 to 6 m² per coat from a 1000 ml tin by brush; a dipped stator takes more because the winding absorbs varnish. A typical 15 kW motor rewind uses most of one litre for two coats.
Is insulating varnish the same as impregnating resin?
No. Varnish is a solvent or water-based coating that dries to a film and is used for finishing and maintenance; impregnating resin is solventless, fills the whole winding under dip, trickle or vacuum-pressure impregnation and is cured in an oven, mainly in production and major rewinds.
Does the varnish withstand Saudi heat and humidity?
A class F varnish is rated for 155 °C continuous winding temperature, far above any ambient; the moisture-resistant film is what protects windings in the humid coastal cities. Store the tin out of the sun and apply thin coats so the film cures through.
Do you have the safety data sheet?
Yes. The technical data sheet is on the product page and the safety data sheet comes with the quotation on request; the product is classified flammable, so use it in a ventilated area away from ignition sources.
Need these items? Send your list or a nameplate photo; your quotation arrives within 24 hours.
This guide is general information. Final selection must follow the project design, the applicable standards and the maker's data.