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Dip and Strip

No-effort paint removal from alloy and steel.

by Julian Edgar

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This article was first published in 1999.

Minus Paint is a South Australian company that specialises in, well... removing paint. They have processes for aluminium, plastic, rubber, mild steel, cast iron and glass. Proprietor David Polklaser was happy to show us around.

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One major job being carried out by the company is the removal of powder coating from these steel and aluminium arms, which are part of a rear vision mirror assembly manufactured by Britax in Australia and exported to the US. Where there are any scratches in the powder coating, the arms are sent to Minus Paint for coating removal, after which the powder coating is reapplied and the arms exported. No corrosion problems have occurred after this process.

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Alloy components are dipped in these 200 litre drums of special chemical. The drums are about three-quarters full, with a layer of water on top preventing evaporation of the expensive liquid. The length of time that the materials stay in the tanks depends on the coating type and thickness, but an hour is typical.

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A high pressure, hot water spray is used to remove the paint after the object has been dipped. Here a turbo alloy intercooler is being cleaned of paint. The cost of removing paint from a radiator or intercooler is about A$40-50.

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These alloy wheels were originally powder coated. The owner decided to have the wheel on the right sandblasted and the wheel on the left chemically cleaned using the bath and water spray technique. The chemically cleaned wheel retained its polished rim while the sandblasted rim had a dull, roughened finish.

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The alloy paint removal process does not harm rubber or plastic, as can be seen from these drive bushes still in place in this motorbike alloy wheel. That means that window and door rubbers can be cleaned of overspray without difficulty.

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For the removal of paint from steel, a huge heated tank of sodium hydroxide (caustic soda) is used. Contrary to popular opinion, this not an acidic solution - it is in fact strongly alkaline. The chemical solution does not attack the steel - in fact, the tank itself is made from steel! It is large enough that a whole car shell can be dipped.

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Panels to be dipped are arranged in a rack with the whole assembly then submerged in the tank overnight. When they came out, the paint on the panels varies from looking like this to appearing almost untouched. Two-pack paints are amongst the toughest.

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The softened paint is stripped using the high pressure water spray. The process is most suitable for pre-1986 cars, with cars made after that date using chemically resistant paints. However, we did spy a current model VT Commodore bootlid that had apparently come from the nearby Holden plant...

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Many older panels have a mixture of paints. Here the original paint on the inner door has gone but the new paint on the outer skin remains. The door will need to go back into the tank for a further dose.

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Here is what a panel looks like when it is fully stripped. Note how every metal surface is now bare - both inside and out. Some people view this as a disadvantage, with complete rust-proofing a necessity after this process has been completed. Getting a panel to this state costs $50-60.

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Not just panels can be stripped. This drag racing diff is being removed of all traces of paint. David made the point that sandblasting could have been a little dangerous with this object - you sure wouldn't want any sand remaining inside... Before painting, David suggests that the dipped object be cleaned with hot, soapy water and then etch-primed.

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Of course, any rust perforations in the panel will still be there after the paint has been removed! In fact, David suggested that his criteria for picking out old panels was a bit different to other people's - he wanted "honest" panels, rather than those that looked pristine but had filler and other repairs in them. This means that he's quite happy to buy panels for his own cars that have a few minor dings and the original paint, knowing that they will clean up well.

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The sodium hydroxide tank is large enough to take full shells like this Ford F100 cab. However, the solution will clean out every surface, including the inside of sill panels and other closed box sections. This means that some holes will need to be drilled if effective painting is to occur within these areas. One interesting aspect of this cabin is you could clearly see the left-hand to right-hand drive conversion workmanship - which wasn't great.

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While the process removes most body fillers and caulking compounds, a few don't budge. This means that some work still needs to be done by hand, for example in removing this material from seams. Dipping a whole shell costs about $750 for a mid-sized car. David stressed that this did not include the doors, suspension, etc!

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A further two dips are available. One is used to neutralise and remove rust, and the other to coat panels with a water-based sealant to prevent corrosion during transport and short-term storage.

Contact:

Minus Paint
+61 8 8243 2899

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