Air-drying or baking winding varnish?

The basic difference: how the varnish hardens

Air-drying varnish hardens at room temperature as its solvent evaporates and the varnish is exposed to air. No oven, heater or special equipment is needed; the varnished motor is simply left to dry.

Baking varnish cures with heat. When baked at the recommended temperature and time, the resin fully cross-links and turns the winding into a single hard body. Left in air, it does not cure fully.

Comparison

Which one, when?

Choose air-drying if:

• you have no oven, or the motor does not fit in it,
• you run a repair shop and different motors come in every day,
• you work in the field without removing the motor,
• you are winding a general-purpose motor that runs in normal conditions.

Choose baking if:

• you do series winding and want the same quality in every motor,
• the motor will run with vibration, at high speed or under heavy load,
• the winding will operate in humid environments, in a submersible pump or in hot oil,
• you have an oven and can schedule the work.

If you are undecided, ask: what would it cost if this motor came back? For heavy-duty motors whose failure would be expensive, baking varnish is the safer choice.

How to apply air-drying varnish

1. Clean the winding; preheat old motors to drive out moisture.
2. Thin the varnish with its own thinner (T-100), generally 3 parts varnish to 1 part thinner.
3. Dip, or work it well into the winding with a brush.
4. Drain off the excess; do not leave pools.
5. Leave it to dry in a warm, dry, ventilated place for the time stated in the TDS.

How to apply baking varnish

1. Clean the winding and dry it by preheating.
2. Thin the varnish with its own thinner (T-300), generally 3 parts varnish to 1 part thinner.
3. Impregnate by dipping; keep it immersed until bubbles stop rising.
4. Drain off the excess.
5. Put it in the oven and apply the recommended temperature–time schedule. Start timing once the part reaches oven temperature.
6. Do not take it out before the time is up; let the motor cool completely before running it.

For thinner choice and ratio, see our thinner guide.

Using both together

For a workshop without an oven whose motor will run in harsh conditions, there is a practical route: varnish the winding with air-drying OR 1xx and, once fully dry, apply an insulating top coat. The top coat adds an extra layer of protection against moisture and corrosion. For touch-ups on connections and terminals, use motor insulating spray.

Common mistakes

• Leaving baking varnish to air-dry: the surface may look dry, but it does not cure and stays tacky. See our guide on why winding varnish won't dry.
• Mixing the two types in one tank: air-drying and baking varnish must not be added to each other; drying is impaired.
• Mixing thinners: do not add T-300 to air-drying varnish or T-100 to baking varnish.
• Trying to air-dry in a cold workshop: drying takes far longer; move the motor somewhere warm.