Friday, March 9, 2012

Bubble Repair

As I mentioned in the previous post, the powder coating process was mostly successful.  The problem was that bubbles appeared on the bed surface. 

Bubbles on bed    Bubbles close-up

I discussed possible causes of the bubbles with my husband, who has much more experience in powder coating than I do.  He said it could be due to any number of reasons, including either porous metal or contaminants trapped in the metal.  The air or contaminants (such as oil) trapped in the metal would start to expand as the metal is heated in the oven at temperatures up to the 400°F that is required to liquefy and cure the powder coating.  The bubbles then form as the contaminants escape through the powder coating.  However, he points out that this is all speculation on his part and the true cause remains unknown.  All I know is that Ms. Rusty looks like she has a bad case of acne and I need to fix it!

I decided to use elbow grease to sand away the bubbles.  My supplies for this task were found in the paint department of the local Home Depot.  I bought a sanding block with 220 grit sand paper to knock down the big bumps and a 320 grit to smooth out the surface.  I also picked up a bag of #000 steel wool to make the surface as smooth as possible.

sanding supplies

After an hour of sanding the bed, all the bubbles were gone and the surface was as soft and smooth as a baby’s bottom.  There are still little pock-marks were the bubbles were, but I don’t think it is possible to completely eliminate them without sanding down to the bare metal.

another view after sandingBack of Bed after sanding

Close-up:  close-up after sanding

Because the bed now has a dull surface, I decided to apply a coat of clear Krylon Fusion (see previous post) to make everything nice and shiny before applying the decals.  I taped off the bobbin area to avoid too much build up of paint which could make fitting the slide plates difficult.

taped up bobbin area

The clear coat dried really fast (< an hour) and Ms. Rusty looks really pretty from a few feet away!

After clearcoatrear view after clear coat

However, if you get closer, you can see where all the bubbles were on the bed.  It isn’t pretty to look at, but the bed is really smooth so fabric will slide over the bed like butter on a hot griddle!

close-up after clearcoat

Ms. Rusty isn’t perfect, but I’m happy with the way things turned out so far.  She looks much better than before.  And more importantly, the metal is completely protected and rust-free, so she’s no longer at risk of  rotting away, which was one of my main goals.

The next step step in the process is applying decals.  That should be fun!!!


  1. Ms Rusty with the bubble (before sanding) looks better than my Singer 15 that is missing half the paint on the bed and has silvered decals. As long as she sews nicely.... Ms Rusty is looking pretty nice now.

  2. I love it. I might have gone for something like bright red or orange, though, if I were going to all that trouble.

    I'm looking forward to seeing this finished.

  3. Was it just the bed that got the bubbles? That's interesting in itself, although I have NO idea what it might mean.

    thanks again for all the great info
    Cheryl Warren

  4. You are amazing!!! She looks beautiful; pock marks and all. Just imagine your first stitches with her. Oh what fun.....


  5. Thank you all for your comments!! Each time I think I'm getting ahead I run into yet another problem, so it's encouraging to read your kind words :)

  6. Hi I am a painter/sprayer for 24 years now and based in the UK. I would say your husbands speculation of oil contaminants in the metal is correct, it also looks like that to my eye. Old Cast iron is notoriously known as a porous metal because of "gas porosity" when casting, this creates tiny bubbles, (often naked to the eye) in the cast iron, and on the surface. Your bubbling looks too big to be just this alone, so I am with your husband and say that it is indeed machine oil reacting with the powder coat on melt.

    I have a Singer 99 hand crank to restore for myself and was looking for info/leads on decals for it. I like what you are doing and wish you much success with it and fun using it afterwards.

    Best wishes

    1. Thanks for the input, Darron. It makes me feel better knowing that in some ways the bubbles would have been hard/impossible to avoid. You may have some luck finding decals at He has some Singer 99 decals and that is where I bought my decals. Great service and a great, easy to use, product. Best of luck on your restoration!