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Lurch

DeRusting with Molasses

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Posted (edited)

I thought everyone might be interested in how I used Molasses to de-rust a bonnet.
It may be applicable to members who wish to derust a metal item without resorting to media blasting.


Backstory: 
I'm helping my brother restore his Mk1 Austin Healey Sprite. 

When he bought the Sprite as a disassembled project, it came with a repoduction fiberglass bonnet. Originally these cars came with a one piece steel bonnet and Brotato
wanted to restore the Sprite with an original steel item - problem being, these are now rare and good bonnets command silly prices.

He found a bonnet on Gumtree in Perth that was a bit sad in condition, but it was complete and fairly unmolested. 
It had however been media blasted, given a light coat of Red Oxide then left to rust some 15+ years ago.
He bought it for a few hundred dollars and I had it shipped over.

Now I didn't want to have it Garnet blasted again to remove the rust and risk warping the already thin steel.
Soda blasting was out as it won't effectively remove rust this ingrained, it could also warp the panels and it's an expensive process to have done.
I considered sanding & wire buffing the rust then applying phosphoric acid, but this is laborious and probably won't remove every last spec of rust.

The Molasses bath seemed like the best solution as I had success with this technique before on engine tinware (rocker covers, timing covers etc).
So we unpicked the guards off the centre section of the bonnet - as the T-beading had rusted away and would have to be replaced - as well as the radiator intake ducting etc.
I then went on eBay and bought a cheap 800ltr inflatable pool for about $140, bought 40ltrs of stock feed Molasses, filled the pool up with water and immersed the bonnet in it:

We then mixed in the Molasses covering the part of the bonnet we wanted to de-rust (we are replacing the lower valance as it's beyond repair) :

 

 

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Edited by Lurch

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Note: I can't  post photos in order due to the new forum software.

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Posted (edited)

We then covered it over with a tarp and left it to do it's thing.
A few weeks later we exhumed it for the mix to find that the rust was totally eaten away:

A scrub with a scotch brite pad and wire brush while hosing the Molasses goo and remaining scale off with water left us with a rust free bonnet:

Showing the line where the Molasses sat at:

At this point the bonnet had flash rusted from being exposed to water and atmosphere, so I sat it in front of my Jetfire diesel heater to dry off.

Once dry I we gave it a coating of Phosphoric Acid to remove the flash rust and left it to dry:

The remaining red marks are painted lead & body filler which I have now removed. 
I just haven't had a chance to take a photo of the bonnet as it sits now, but IMHO this is the cheapest (under $200) and easiest way to de-rust this panel.
Now we just have to do the guards & radiator ducting. I'll add some more photos to this thread when we've got all the parts/panels done.

 

 

 

 

 

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Edited by Lurch

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Good one sir. Love the use of the kiddies pool. 8)

I was pretty impressed with my results and will be using this method again. I found surface rust take hold as the metal dried but that was easy to deal with in comparison to what was there previously.

The more pitting there is the more reason to use molasses.

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Lachlan, how do you deal with the deeper pitting on the bonnet?

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Depending on how bad the pitting is, either weld the pits up or wipe with metal-mend filler.
If it's a large badly pitted section, it would need to be cut out & replaced.

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Posted (edited)
1 hour ago, Lurch said:

....... wipe with metal-mend filler.
.......... 

Hey Lurch, 

Would be interested in recommended products. As this is something I haven't had a any experience with. 

Or are you simply referring to standard body filler?

Please excuse my ignorance, just starting to feel my way around this speciality :)

 

Cheers, 

Rob 

Edited by RAP260

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2 hours ago, RAP260 said:

Hey Lurch, 

Would be interested in recommended products. As this is something I haven't had a any experience with. 

Or are you simply referring to standard body filler?

Please excuse my ignorance, just starting to feel my way around this speciality :)

 

Cheers, 

Rob 

Hi Rob,
It's basically a 2-part epoxy metastatic filler - most body shops carry it in one brand or another.
It's not designed to be used as body filler though, but it's great if you have rust pitting or filling a pin-hole that isn't able to be welded (for whatever reason).

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On 6/13/2018 at 9:45 PM, gav240z said:

Good for steel wheels!

Reminds me of this video.

 

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Hey mate, I forgot to ask you the other day, with the parts I am cleaning up, and figured here would be the best place to ask.

After I pull out these parts from Molasses bath, I am not sure how to treat the inside of this valve or if i should. And do you see any issues with spraying the outside with High Heat enamel on the parts where the coolant hose will clamp onto?

Cheers, 

Ned

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