Wednesday, February 26, 2014

(de) Pressed Tin

Before, during and after
After restoring 10 sheets of antique pressed tin for our bathroom ceiling I feel that I'm somewhat of an authority on the subject.  At least on the topic of how to prepare and paint the stuff - but it did take some experimentation.

Plan A for ridding the decades of paint, dirt and unidentifiable gunk was a wire brush on an electric drill.  15 seconds later I'd only melted the layers into a very robust, potentially Nobel prize winning composite that adhered to the tin better than ever.  I changed tack and resorted to plan B, the 600c hot air gun.
This also worked to consolidate the surface into a single layer; much like a slice of cheese, but in contrast to plan A it weakened the grip between the tin and the surface.  But if I overheated it I ended up with something more like butter than cheddar, which was easier to spread but decidedly harder to remove, especially once it became cold.
Whilst effective the hot air gun was tediously slow and incredibly messy as it took a few passes to remove the melted goo completely.  Two sheets along it dawned on me that perhaps a combination of the two approaches, hot air and wire wheel, might work. 
So after some more fiddling I came up with the following modus operandi which was about 30% quicker than relying on just the hot air gun:
  • Heat an area of about 30cm x 30cm until the finish just starts to bubble (cheese not butter).  This weakened the connection between the tin and the coating.
  • Allow to cool for a couple of minutes.  This resulted in the surface becoming very brittle.
  • Scrape the surface with the back of a chisel.  For me this removed around 90% of the paint and made far less mess than the wire brush did when it flicked chips at 257km/h all over the shop.
  • Run over the remainder with the drill/wire brush combo.  The resulting surface was 99.9% clean – or better.
Including the subsequent panel beating and applications of rust converter, red oxide primer and undercoat each sheet took hours and hours to prepare.
Have I mentioned I’m not going to recycle a pressed tin ceiling again?