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Problems using regular enamel paint in microwave oven?

Discussion in 'Electronic Repair' started by Sam Goldwasser, Apr 5, 2007.

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  1. Has anyone seen problems using common hardware store gloss enamel to
    touch up a microwave oven interior?

    Someone emailed me all in a huff that they followed this advise and it now
    smells "funky" and smokes. They said the paint color was white and they
    waited 24 hours before use. This was apparently under the turntable.

    The smell could make sense if there was some residual solvent present and
    should go away after awhile, but the "smokes" part is strange unless they
    didn't bother to clean and sand beforehand and there was trapped debris.

    Any comments appreciated.

    --- sam | Sci.Electronics.Repair FAQ:
    Repair | Main Table of Contents:
    +Lasers | Sam's Laser FAQ:
    | Mirror Sites:

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
  2. Ron(UK)

    Ron(UK) Guest

    We used to use[1] Humbrol model kit paint without any problems, indeed,
    the 'proper stuff' came from the Humbrol factory and looked and smelled
    exactly like the model enamel, only five times the price!

    [1] back in the days when microwave oven repairs were financially viable

  3. hr(bob)

    hr(bob) Guest


    I think you are 100% correct. There should be no hot spots anywhere
    on the uwave oven liner as it is a solid metal sheet except where the
    uwaves come into the chamber. There is obviously a fault of some type
    that is making that area of the uwave get hot or there would not be
    any smoke. That may be why there was a fault in the original paint at
    the location.

    BTW - I think you are right on in just about everthing you recommend,
    and your repair faq stuff is a great resource.

    H. R.(BOb) HOfmann
  4. GregS

    GregS Guest

    Some black paints are electrically conductive, but even that should be no problem unless
    it was across an insulator like glass. Probably just the residuals from a little heat and moisture
    from normal cooking. The oven should have been baked. Did I say that right? At least
    a hot air gun or hair dryer shold ahve been used to treat the paint first.

  5. GregS

    GregS Guest

    Come to think of it, materials can be lossy at microwave frequency, so
    even if it were not dc conductive, a material could heat up if were suspended
    across an insulator.

    My black electrically conductive seal on the old Heathkit microwave,
    use to kind of melt.

  6. Guest


    A couple of things come to mind, both of them pretty remote:

    a) the batch of paint used had Titanium Dioxide as the white pigment.
    It is just possible that the paint as-applied was more absorbtive than
    the OEM paint & metal combination and so that area turned into a 'hot-
    spot'. If they did an area say the size of a business card or more,
    that would be the second thing that came to mind and that based only
    on very careful prep... see b) below.
    b) conversely and more likely, the prep-work took the microwave-
    reflective primer off and exposed the steel. BAD MOVE as without that
    reflective coating the metal will get very hot no matter what sort of
    finish coating may be on top.

    Just my random thoughts.

    Peter Wieck
    Wyncote, PA
  7. Guest

    Does anyone agree with this?
  8. Guest

    To understand what the walls of the oven are made of or what material
    one could use to partially keep food from cooking, you have to have
    some knowledge of 'dielectric constant' and 'loss tangent'. The
    materials used for protectors can be plastics, ceramics.... all
    depends on the dielectric constant and the RF properties at 2.45 GHz.
    The walls are usually a light sheet metal (or plastic with a layer of
    metal foil) with a dissipative coating.

    from: Ronna Erickson
    Radio Astronomy, Univ. of Mass. - Amherst

    Remove that dissipative coating and Bob's your Uncle...

    In any quality oven, that coating is fired enamel and pretty tough. In
    the cheaper versions, it is a powder-coating that is fragile at best
    if abrasives are used to clean. On some others, it is back-coated onto
    a tough plastic... That is the hardest to damage.

    Peter Wieck
    Wyncote, PA
  9. Does that apply only if there's a coating on top of the metal?
    Because we have a microwave oven with a stainless steel interior
  10. So how is stainless steel different than steel, microwave-wise? To reflect
    microwaves implies a conductive material. The conductivity may be different,
    but not dramatically.

    --- sam | Sci.Electronics.Repair FAQ:
    Repair | Main Table of Contents:
    +Lasers | Sam's Laser FAQ:
    | Mirror Sites:

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
  11. Guest

    There are several patterns to how the magnetron works, and several
    methods to spread the pattern over the food. "Better" ovens use a
    combination of reflection and absorbtion to make the food cook evenly,
    *in addition* to either a turntable or even the figure-8 pattern
    turntables on some higher-end ovens. In these cases, the Turntable
    platter and mechanism serves as the absorber, the vertical surfaces
    will be the refectors.

    In the cheaper fixed-position ovens where one is required to rotate
    items or turn them over, the niceties of such designs are ignored and
    the magnetron pretty much blasts in whatever pattern it is masked to
    do. Scatter is to be absorbed by the surfaces of the oven.

    There is a great deal of thought and design that is hidden in these
    beasts. It is absolutely possible to put out an oven at US$39 that
    will both cool and still make a profit for the retailer even after it
    is shipped from China. It is also possible to spend $600 for an oven
    that will not only cook but have all of these design niceties included
    and still make a profit for the dealer even after it has been shipped
    from China.

    Point being that everything inside that oven, right down to the paint,
    has been chosen for the purpose. And if they are stainelss steel
    lined, that steel has also been 'designed' for the purpose. Can't go
    by smell on the paint, can't go by looks on the steel.

    Peter Wieck
    Wyncote, PA
  12. Guest

    Maybe you dont repair microwaves.

  13. Guest

    Put as simply as possible, I would not, no. And this from someone
    whose hobby (amongst others) is restoring vintage radios and audio
    equipment from the 20s - 70s.

    Peter Wieck
    Wyncote, PA
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