Ultrasonic NaOH paint stripping

[Rob de Bie]

Almost by accident I discovered a perfect way to strip off paint from plastic models. In the past I always used sodium hydroxide (NaOH) oven cleaner from a spray can, that worked well but slow, and often required multiple applications and considerably scrubbing. But when I combined it with an ultrasonic cleaner I found the perfect method: all paint and decals were removed in 10-20 minutes without any oaint traces. The technique described here works on enamel paint, I haven't tried other paints yet. Just as an example, I would first try ammonia water (4%) for acrylic paints.

 

Shown here are the two main ingredients: sodium hydroxide (NaOH, lye and caustic soda in the US) and an ultrasonic cleaner. I used a drain opener that is a solution of approximately 10% NaOH in water and probably nothing else. I diluted it further down by adding water, to maybe 5%.

 

From what I read, stainless steel is not attacked by NaOH below 65C, but still I put the NaOH solution a separate plastic container, suspended in the metal wire basket that comes with the ultrasonic cleaner. There are no liquids in the photo, I did not want to get my photo set-up wet!

 

 

This is the model I wanted to strip: a 35 year old Tamiya 1/20 McLaren M23. I used a Humbrol enamel spray can for the white, and brush-painted everything else with Humbrol enamels. I remember overpainting the large red-orange decal areas with red paint some time later.

 

 

All paint and decals were removed in 10-20 minutes. The parts were perfectly clean without any further effort, no scrubbing or anything.

 

 

Interestingly all glue joints also broke down during the paint stripping, a unexpected but great benefit. I removed the worst remains of the tube glue with a JLC razor blade used as a scraper.

 

Warning: be careful handling NaOH! Your eyes are at risk, use safety glasses. Gloves are recommended too, otherwise your skin will start to feel greasy and slippery, because it's slowly dissolving.

Rob

[dnl42]

Brilliant!

 

1 hour ago, Rob de Bie said:

From what I read, stainless steel is not attacked by NaOH below 65C, but still I put the NaOH solution a separate plastic container, suspended in the metal wire basket that comes with the ultrasonic cleaner. There are no liquids in the photo, I did not want to get my photo set-up wet!

 

  

 

Just to be clear, you filled the plastic tub containing the part with watered-down NaOH, a.k.a., over cleaner, almost to the rim. You then filled the cleaner's tub with water until the water level was just below the lip of the plastic tub.

Is that correct?

[Rob de Bie]

1 hour ago, dnl42 said:

Just to be clear, you filled the plastic tub containing the part with watered-down NaOH, a.k.a., over cleaner, almost to the rim. You then filled the cleaner's tub with water until the water level was just below the lip of the plastic tub.

Is that correct?

 

Correct, except not filled to the brim, to avoid spilling the NaOH into the ultrasonic cleaner. If the part is not submerged completely, turn it over after 10 minutes.

 

Rob

[skyhawk174]

Great tip Rob. Used my cleaner for cleaning my airbrush but never to strip paint. May have to remember this. My cleaner is not so big so I may need to get a new one if I ever need to do this.